Merge pull request #1406 from whitequark/connect_rpc

rpc: new frontend

11 files changed, 1767 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 75d3097a3..2644721be 100644
--- a/Makefile
+++ b/Makefile
@@ -528,6 +528,7 @@ $(eval $(call add_include_file,kernel/satgen.h))
 $(eval $(call add_include_file,libs/ezsat/ezsat.h))
 $(eval $(call add_include_file,libs/ezsat/ezminisat.h))
 $(eval $(call add_include_file,libs/sha1/sha1.h))
+$(eval $(call add_include_file,libs/json11/json11.hpp))
 $(eval $(call add_include_file,passes/fsm/fsmdata.h))
 $(eval $(call add_include_file,frontends/ast/ast.h))
 $(eval $(call add_include_file,backends/ilang/ilang_backend.h))
@@ -545,6 +546,8 @@ OBJS += libs/sha1/sha1.o
 
 ifneq ($(SMALL),1)
 
+OBJS += libs/json11/json11.o
+
 OBJS += libs/subcircuit/subcircuit.o
 
 OBJS += libs/ezsat/ezsat.o
@@ -710,6 +713,7 @@ test: $(TARGETS) $(EXTRA_TARGETS)
 	+cd tests/aiger && bash run-test.sh $(ABCOPT)
 	+cd tests/arch && bash run-test.sh
 	+cd tests/ice40 && bash run-test.sh $(SEEDOPT)
+	+cd tests/rpc && bash run-test.sh
 	@echo ""
 	@echo "  Passed \"make test\"."
 	@echo ""
diff --git a/frontends/rpc/Makefile.inc b/frontends/rpc/Makefile.inc
new file mode 100644
index 000000000..9af505098
--- /dev/null
+++ b/frontends/rpc/Makefile.inc
@@ -0,0 +1,2 @@
+
+OBJS += frontends/rpc/rpc_frontend.o
diff --git a/frontends/rpc/rpc_frontend.cc b/frontends/rpc/rpc_frontend.cc
new file mode 100644
index 000000000..b4b2fa3a2
--- /dev/null
+++ b/frontends/rpc/rpc_frontend.cc
@@ -0,0 +1,589 @@
+/*
+ *  yosys -- Yosys Open SYnthesis Suite
+ *
+ *  Copyright (C) 2019  whitequark <whitequark@whitequark.org>
+ *
+ *  Permission to use, copy, modify, and/or distribute this software for any
+ *  purpose with or without fee is hereby granted, provided that the above
+ *  copyright notice and this permission notice appear in all copies.
+ *
+ *  THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ *  WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ *  MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ *  ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ *  WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ *  ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ *  OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ */
+
+// The reason the -path mode of connect_rpc uses byte-oriented and not message-oriented sockets, even though
+// it is a message-oriented interface, is that the system can place various limits on the message size, which
+// are not always transparent or easy to change. Given that generated HDL code get be extremely large, it is
+// unwise to rely on those limits being large enough, and using byte-oriented sockets is guaranteed to work.
+
+#ifndef _WIN32
+#include <unistd.h>
+#include <spawn.h>
+#include <sys/wait.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#endif
+
+#include "libs/json11/json11.hpp"
+#include "libs/sha1/sha1.h"
+#include "kernel/yosys.h"
+
+YOSYS_NAMESPACE_BEGIN
+
+#if defined(_WIN32)
+static std::wstring str2wstr(const std::string &in) {
+    if(in == "") return L"";
+    std::wstring out;
+    out.resize(MultiByteToWideChar(/*CodePage=*/CP_UTF8, /*dwFlags=*/0, /*lpMultiByteStr=*/&in[0], /*cbMultiByte=*/(int)in.length(), /*lpWideCharStr=*/NULL, /*cchWideChar=*/0));
+    int written = MultiByteToWideChar(/*CodePage=*/CP_UTF8, /*dwFlags=*/0, /*lpMultiByteStr=*/&in[0], /*cbMultiByte=*/(int)in.length(), /*lpWideCharStr=*/&out[0], /*cchWideChar=*/(int)out.length());
+    log_assert(written == (int)out.length());
+    return out;
+}
+
+static std::string wstr2str(const std::wstring &in) {
+	if(in == L"") return "";
+	std::string out;
+	out.resize(WideCharToMultiByte(/*CodePage=*/CP_UTF8, /*dwFlags=*/0, /*lpWideCharStr=*/&in[0], /*cchWideChar=*/(int)in.length(), /*lpMultiByteStr=*/NULL, /*cbMultiByte=*/0, /*lpDefaultChar=*/NULL, /*lpUsedDefaultChar=*/NULL));
+	int written = WideCharToMultiByte(/*CodePage=*/CP_UTF8, /*dwFlags=*/0, /*lpWideCharStr=*/&in[0], /*cchWideChar=*/(int)in.length(), /*lpMultiByteStr=*/&out[0], /*cbMultiByte=*/(int)out.length(), /*lpDefaultChar=*/NULL, /*lpUsedDefaultChar=*/NULL);
+	log_assert(written == (int)out.length());
+	return out;
+}
+
+static std::string get_last_error_str() {
+	DWORD last_error = GetLastError();
+	LPWSTR out_w;
+	DWORD size_w = FormatMessageW(/*dwFlags=*/FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_IGNORE_INSERTS, /*lpSource=*/NULL, /*dwMessageId=*/last_error, /*dwLanguageId=*/0, /*lpBuffer=*/(LPWSTR)&out_w, /*nSize=*/0, /*Arguments=*/NULL);
+	if (size_w == 0)
+		return std::to_string(last_error);
+	std::string out = wstr2str(std::wstring(out_w, size_w));
+	LocalFree(out_w);
+	return out;
+}
+#endif
+
+using json11::Json;
+
+struct RpcServer {
+	std::string name;
+
+	RpcServer(const std::string &name) : name(name) { }
+	virtual ~RpcServer() { }
+
+	virtual void write(const std::string &data) = 0;
+	virtual std::string read() = 0;
+
+	Json call(const Json &json_request) {
+		std::string request;
+		json_request.dump(request);
+		request += '\n';
+		log_debug("RPC frontend request: %s", request.c_str());
+		write(request);
+
+		std::string response = read();
+		log_debug("RPC frontend response: %s", response.c_str());
+		std::string error;
+		Json json_response = Json::parse(response, error);
+		if (json_response.is_null())
+			log_cmd_error("parsing JSON failed: %s\n", error.c_str());
+		if (json_response["error"].is_string())
+			log_cmd_error("RPC frontend returned an error: %s\n", json_response["error"].string_value().c_str());
+		return json_response;
+	}
+
+	std::vector<std::string> get_module_names() {
+		Json response = call(Json::object {
+			{ "method", "modules" },
+		});
+		bool is_valid = true;
+		std::vector<std::string> modules;
+		if (response["modules"].is_array()) {
+			for (auto &json_module : response["modules"].array_items()) {
+				if (json_module.is_string())
+					modules.push_back(json_module.string_value());
+				else is_valid = false;
+			}
+		} else is_valid = false;
+		if (!is_valid)
+			log_cmd_error("RPC frontend returned malformed response: %s\n", response.dump().c_str());
+		return modules;
+	}
+
+	std::pair<std::string, std::string> derive_module(const std::string &module, const dict<RTLIL::IdString, RTLIL::Const> &parameters) {
+		Json::object json_parameters;
+		for (auto &param : parameters) {
+			std::string type, value;
+			if (param.second.flags & RTLIL::CONST_FLAG_REAL) {
+				type = "real";
+				value = param.second.decode_string();
+			} else if (param.second.flags & RTLIL::CONST_FLAG_STRING) {
+				type = "string";
+				value = param.second.decode_string();
+			} else if ((param.second.flags & ~RTLIL::CONST_FLAG_SIGNED) == RTLIL::CONST_FLAG_NONE) {
+				type = (param.second.flags & RTLIL::CONST_FLAG_SIGNED) ? "signed" : "unsigned";
+				value = param.second.as_string();
+			} else
+				log_cmd_error("Unserializable constant flags 0x%x\n", param.second.flags);
+			json_parameters[param.first.str()] = Json::object {
+				{ "type", type },
+				{ "value", value },
+			};
+		}
+		Json response = call(Json::object {
+			{ "method", "derive" },
+			{ "module", module },
+			{ "parameters", json_parameters },
+		});
+		bool is_valid = true;
+		std::string frontend, source;
+		if (response["frontend"].is_string())
+			frontend = response["frontend"].string_value();
+		else is_valid = false;
+		if (response["source"].is_string())
+			source = response["source"].string_value();
+		else is_valid = false;
+		if (!is_valid)
+			log_cmd_error("RPC frontend returned malformed response: %s\n", response.dump().c_str());
+		return std::make_pair(frontend, source);
+	}
+};
+
+struct RpcModule : RTLIL::Module {
+	std::shared_ptr<RpcServer> server;
+
+	RTLIL::IdString derive(RTLIL::Design *design, dict<RTLIL::IdString, RTLIL::Const> parameters, bool /*mayfail*/) YS_OVERRIDE {
+		std::string stripped_name = name.str();
+		if (stripped_name.compare(0, 9, "$abstract") == 0)
+			stripped_name = stripped_name.substr(9);
+		log_assert(stripped_name[0] == '\\');
+
+		log_header(design, "Executing RPC frontend `%s' for module `%s'.\n", server->name.c_str(), stripped_name.c_str());
+
+		std::string parameter_info;
+		for (auto &param : parameters) {
+			log("Parameter %s = %s\n", param.first.c_str(), log_signal(RTLIL::SigSpec(param.second)));
+			parameter_info += stringf("%s=%s", param.first.c_str(), log_signal(RTLIL::SigSpec(param.second)));
+		}
+
+		std::string derived_name;
+		if (parameters.empty())
+			derived_name = stripped_name;
+		else if (parameter_info.size() > 60)
+			derived_name = "$paramod$" + sha1(parameter_info) + stripped_name;
+		else
+			derived_name = "$paramod" + stripped_name + parameter_info;
+
+		if (design->has(derived_name)) {
+			log("Found cached RTLIL representation for module `%s'.\n", derived_name.c_str());
+		} else {
+			std::string command, input;
+			std::tie(command, input) = server->derive_module(stripped_name.substr(1), parameters);
+
+			std::istringstream input_stream(input);
+			RTLIL::Design *derived_design = new RTLIL::Design;
+			Frontend::frontend_call(derived_design, &input_stream, "<rpc>" + derived_name.substr(8), command);
+			derived_design->check();
+
+			dict<std::string, std::string> name_mangling;
+			bool found_derived_top = false;
+			for (auto module : derived_design->modules()) {
+				std::string original_name = module->name.str();
+				if (original_name == stripped_name) {
+					found_derived_top = true;
+					name_mangling[original_name] = derived_name;
+				} else {
+					name_mangling[original_name] = derived_name + module->name.str();
+				}
+			}
+			if (!found_derived_top)
+				log_cmd_error("RPC frontend did not return requested module `%s`!\n", stripped_name.c_str());
+
+			for (auto module : derived_design->modules())
+				for (auto cell : module->cells())
+					if (name_mangling.count(cell->type.str()))
+						cell->type = name_mangling[cell->type.str()];
+
+			for (auto module : derived_design->modules_) {
+				std::string mangled_name = name_mangling[module.first.str()];
+
+				log("Importing `%s' as `%s'.\n", log_id(module.first), log_id(mangled_name));
+
+				module.second->name = mangled_name;
+				module.second->design = design;
+				module.second->attributes.erase("\\top");
+				design->modules_[mangled_name] = module.second;
+				derived_design->modules_.erase(module.first);
+			}
+
+			delete derived_design;
+		}
+
+		return derived_name;
+	}
+
+	RTLIL::Module *clone() const YS_OVERRIDE {
+		RpcModule *new_mod = new RpcModule;
+		new_mod->server = server;
+		cloneInto(new_mod);
+		return new_mod;
+	}
+};
+
+#if defined(_WIN32)
+
+struct HandleRpcServer : RpcServer {
+	HANDLE hsend, hrecv;
+
+	HandleRpcServer(const std::string &name, HANDLE hsend, HANDLE hrecv)
+		: RpcServer(name), hsend(hsend), hrecv(hrecv) { }
+
+	void write(const std::string &data) YS_OVERRIDE {
+		log_assert(data.length() >= 1 && data.find('\n') == data.length() - 1);
+		ssize_t offset = 0;
+		do {
+			DWORD data_written;
+			if (!WriteFile(hsend, &data[offset], data.length() - offset, &data_written, /*lpOverlapped=*/NULL))
+				log_cmd_error("WriteFile failed: %s\n", get_last_error_str().c_str());
+			offset += data_written;
+		} while(offset < (ssize_t)data.length());
+	}
+
+	std::string read() YS_OVERRIDE {
+		std::string data;
+		ssize_t offset = 0;
+		while (data.length() == 0 || data[data.length() - 1] != '\n') {
+			data.resize(data.length() + 1024);
+			DWORD data_read;
+			if (!ReadFile(hrecv, &data[offset], data.length() - offset, &data_read, /*lpOverlapped=*/NULL))
+				log_cmd_error("ReadFile failed: %s\n", get_last_error_str().c_str());
+			offset += data_read;
+			data.resize(offset);
+			size_t term_pos = data.find('\n', offset);
+			if (term_pos != data.length() - 1 && term_pos != std::string::npos)
+				log_cmd_error("read failed: more than one response\n");
+		}
+		return data;
+	}
+
+	~HandleRpcServer() {
+		CloseHandle(hsend);
+		if (hrecv != hsend)
+			CloseHandle(hrecv);
+	}
+};
+
+#else
+
+struct FdRpcServer : RpcServer {
+	int fdsend, fdrecv;
+	pid_t pid;
+
+	FdRpcServer(const std::string &name, int fdsend, int fdrecv, pid_t pid = -1)
+		: RpcServer(name), fdsend(fdsend), fdrecv(fdrecv), pid(pid) { }
+
+	void check_pid() {
+		if (pid == -1) return;
+		// If we're communicating with a process, check that it's still running, or we may get killed with SIGPIPE.
+		pid_t wait_result = ::waitpid(pid, NULL, WNOHANG);
+		if (wait_result == -1)
+			log_cmd_error("waitpid failed: %s\n", strerror(errno));
+		if (wait_result == pid)
+			log_cmd_error("RPC frontend terminated unexpectedly\n");
+	}
+
+	void write(const std::string &data) YS_OVERRIDE {
+		log_assert(data.length() >= 1 && data.find('\n') == data.length() - 1);
+		ssize_t offset = 0;
+		do {
+			check_pid();
+			ssize_t result = ::write(fdsend, &data[offset], data.length() - offset);
+			if (result == -1)
+				log_cmd_error("write failed: %s\n", strerror(errno));
+			offset += result;
+		} while(offset < (ssize_t)data.length());
+	}
+
+	std::string read() YS_OVERRIDE {
+		std::string data;
+		ssize_t offset = 0;
+		while (data.length() == 0 || data[data.length() - 1] != '\n') {
+			data.resize(data.length() + 1024);
+			check_pid();
+			ssize_t result = ::read(fdrecv, &data[offset], data.length() - offset);
+			if (result == -1)
+				log_cmd_error("read failed: %s\n", strerror(errno));
+			offset += result;
+			data.resize(offset);
+			size_t term_pos = data.find('\n', offset);
+			if (term_pos != data.length() - 1 && term_pos != std::string::npos)
+				log_cmd_error("read failed: more than one response\n");
+		}
+		return data;
+	}
+
+	~FdRpcServer() {
+		close(fdsend);
+		if (fdrecv != fdsend)
+			close(fdrecv);
+	}
+};
+
+#endif
+
+// RpcFrontend does not inherit from Frontend since it does not read files.
+struct RpcFrontend : public Pass {
+	RpcFrontend() : Pass("connect_rpc", "connect to RPC frontend") { }
+	void help() YS_OVERRIDE
+	{
+		//   |---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|---v---|
+		log("\n");
+		log("    connect_rpc -exec <command> [args...]\n");
+		log("    connect_rpc -path <path>\n");
+		log("\n");
+		log("Load modules using an out-of-process frontend.\n");
+		log("\n");
+		log("    -exec <command> [args...]\n");
+		log("        run <command> with arguments [args...]. send requests on stdin, read\n");
+		log("        responses from stdout.\n");
+		log("\n");
+		log("    -path <path>\n");
+		log("        connect to Unix domain socket at <path>. (Unix)\n");
+		log("        connect to bidirectional byte-type named pipe at <path>. (Windows)\n");
+		log("\n");
+		log("A simple JSON-based, newline-delimited protocol is used for communicating with\n");
+		log("the frontend. Yosys requests data from the frontend by sending exactly 1 line\n");
+		log("of JSON. Frontend responds with data or error message by replying with exactly\n");
+		log("1 line of JSON as well.\n");
+		log("\n");
+		log("    -> {\"method\": \"modules\"}\n");
+		log("    <- {\"modules\": [\"<module-name>\", ...]}\n");
+		log("    <- {\"error\": \"<error-message>\"}\n");
+		log("        request for the list of modules that can be derived by this frontend.\n");
+		log("        the 'hierarchy' command will call back into this frontend if a cell\n");
+		log("        with type <module-name> is instantiated in the design.\n");
+		log("\n");
+		log("    -> {\"method\": \"derive\", \"module\": \"<module-name\">, \"parameters\": {\n");
+		log("        \"<param-name>\": {\"type\": \"[unsigned|signed|string|real]\",\n");
+		log("                           \"value\": \"<param-value>\"}, ...}}\n");
+		log("    <- {\"frontend\": \"[ilang|verilog|...]\",\"source\": \"<source>\"}}\n");
+		log("    <- {\"error\": \"<error-message>\"}\n");
+		log("        request for the module <module-name> to be derived for a specific set of\n");
+		log("        parameters. <param-name> starts with \\ for named parameters, and with $\n");
+		log("        for unnamed parameters, which are numbered starting at 1.<param-value>\n");
+		log("        for integer parameters is always specified as a binary string of unlimited\n");
+		log("        precision. the <source> returned by the frontend is hygienically parsed\n");
+		log("        by a built-in Yosys <frontend>, allowing the RPC frontend to return any\n");
+		log("        convenient representation of the module. the derived module is cached,\n");
+		log("        so the response should be the same whenever the same set of parameters\n");
+		log("        is provided.\n");
+	}
+	void execute(std::vector<std::string> args, RTLIL::Design *design) YS_OVERRIDE
+	{
+		log_header(design, "Connecting to RPC frontend.\n");
+
+		std::vector<std::string> command;
+		std::string path;
+		size_t argidx;
+		for (argidx = 1; argidx < args.size(); argidx++) {
+			std::string arg = args[argidx];
+			if (arg == "-exec" && argidx+1 < args.size()) {
+				command.insert(command.begin(), args.begin() + argidx + 1, args.end());
+				continue;
+			}
+			if (arg == "-path" && argidx+1 < args.size()) {
+				path = args[argidx+1];
+				continue;
+			}
+			break;
+		}
+		extra_args(args, argidx, design);
+
+		if ((!command.empty()) + (!path.empty()) != 1)
+			log_cmd_error("Exactly one of -exec, -unix must be specified.\n");
+
+		std::shared_ptr<RpcServer> server;
+		if (!command.empty()) {
+			std::string command_line;
+			bool first = true;
+			for (auto &arg : command) {
+				if (!first) command_line += ' ';
+				command_line += arg;
+				first = false;
+			}
+
+#ifdef _WIN32
+			std::wstring command_w = str2wstr(command[0]);
+			std::wstring command_path_w;
+			std::wstring command_line_w = str2wstr(command_line);
+			DWORD command_path_len_w;
+			SECURITY_ATTRIBUTES pipe_attr = {};
+			HANDLE send_r = NULL, send_w = NULL, recv_r = NULL, recv_w = NULL;
+			STARTUPINFOW startup_info = {};
+			PROCESS_INFORMATION proc_info = {};
+
+			command_path_len_w = SearchPathW(/*lpPath=*/NULL, /*lpFileName=*/command_w.c_str(), /*lpExtension=*/L".exe", /*nBufferLength=*/0, /*lpBuffer=*/NULL, /*lpFilePart=*/NULL);
+			if (command_path_len_w == 0) {
+				log_error("SearchPathW failed: %s\n", get_last_error_str().c_str());
+				goto cleanup_exec;
+			}
+			command_path_w.resize(command_path_len_w - 1);
+			command_path_len_w = SearchPathW(/*lpPath=*/NULL, /*lpFileName=*/command_w.c_str(), /*lpExtension=*/L".exe", /*nBufferLength=*/command_path_len_w, /*lpBuffer=*/&command_path_w[0], /*lpFilePart=*/NULL);
+			log_assert(command_path_len_w == command_path_w.length());
+
+			pipe_attr.nLength = sizeof(pipe_attr);
+			pipe_attr.bInheritHandle = TRUE;
+			pipe_attr.lpSecurityDescriptor = NULL;
+			if (!CreatePipe(&send_r, &send_w, &pipe_attr, /*nSize=*/0)) {
+				log_error("CreatePipe failed: %s\n", get_last_error_str().c_str());
+				goto cleanup_exec;
+			}
+			if (!SetHandleInformation(send_w, HANDLE_FLAG_INHERIT, 0)) {
+				log_error("SetHandleInformation failed: %s\n", get_last_error_str().c_str());
+				goto cleanup_exec;
+			}
+			if (!CreatePipe(&recv_r, &recv_w, &pipe_attr, /*nSize=*/0)) {
+				log_error("CreatePipe failed: %s\n", get_last_error_str().c_str());
+				goto cleanup_exec;
+			}
+			if (!SetHandleInformation(recv_r, HANDLE_FLAG_INHERIT, 0)) {
+				log_error("SetHandleInformation failed: %s\n", get_last_error_str().c_str());
+				goto cleanup_exec;
+			}
+
+			startup_info.cb = sizeof(startup_info);
+			startup_info.hStdInput = send_r;
+			startup_info.hStdOutput = recv_w;
+			startup_info.hStdError = GetStdHandle(STD_ERROR_HANDLE);
+			startup_info.dwFlags |= STARTF_USESTDHANDLES;
+			if (!CreateProcessW(/*lpApplicationName=*/command_path_w.c_str(), /*lpCommandLine=*/&command_line_w[0], /*lpProcessAttributes=*/NULL, /*lpThreadAttributes=*/NULL, /*bInheritHandles=*/TRUE, /*dwCreationFlags=*/0, /*lpEnvironment=*/NULL, /*lpCurrentDirectory=*/NULL, &startup_info, &proc_info)) {
+				log_error("CreateProcessW failed: %s\n", get_last_error_str().c_str());
+				goto cleanup_exec;
+			}
+			CloseHandle(proc_info.hProcess);
+			CloseHandle(proc_info.hThread);
+
+			server = std::make_shared<HandleRpcServer>(path, send_w, recv_r);
+			send_w = NULL;
+			recv_r = NULL;
+
+cleanup_exec:
+			if (send_r != NULL) CloseHandle(send_r);
+			if (send_w != NULL) CloseHandle(send_w);
+			if (recv_r != NULL) CloseHandle(recv_r);
+			if (recv_w != NULL) CloseHandle(recv_w);
+#else
+			std::vector<char *> argv;
+			int send[2] = {-1,-1}, recv[2] = {-1,-1};
+			posix_spawn_file_actions_t file_actions, *file_actions_p = NULL;
+			pid_t pid;
+
+			for (auto &arg : command)
+				argv.push_back(&arg[0]);
+			argv.push_back(nullptr);
+
+			if (pipe(send) != 0) {
+				log_error("pipe failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+			if (pipe(recv) != 0) {
+				log_error("pipe failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+
+			if (posix_spawn_file_actions_init(&file_actions) != 0) {
+				log_error("posix_spawn_file_actions_init failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+			file_actions_p = &file_actions;
+			if (posix_spawn_file_actions_adddup2(file_actions_p, send[0], STDIN_FILENO) != 0) {
+				log_error("posix_spawn_file_actions_adddup2 failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+			if (posix_spawn_file_actions_addclose(file_actions_p, send[1]) != 0) {
+				log_error("posix_spawn_file_actions_addclose failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+			if (posix_spawn_file_actions_adddup2(file_actions_p, recv[1], STDOUT_FILENO) != 0) {
+				log_error("posix_spawn_file_actions_adddup2 failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+			if (posix_spawn_file_actions_addclose(file_actions_p, recv[0]) != 0) {
+				log_error("posix_spawn_file_actions_addclose failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+
+			if (posix_spawnp(&pid, argv[0], file_actions_p, /*attrp=*/NULL, argv.data(), environ) != 0) {
+				log_error("posix_spawnp failed: %s\n", strerror(errno));
+				goto cleanup_exec;
+			}
+
+			server = std::make_shared<FdRpcServer>(command_line, send[1], recv[0], pid);
+			send[1] = -1;
+			recv[0] = -1;
+
+cleanup_exec:
+			if (send[0] != -1) close(send[0]);
+			if (send[1] != -1) close(send[1]);
+			if (recv[0] != -1) close(recv[0]);
+			if (recv[1] != -1) close(recv[1]);
+			if (file_actions_p != NULL)
+				posix_spawn_file_actions_destroy(file_actions_p);
+#endif
+		} else if (!path.empty()) {
+#ifdef _WIN32
+			std::wstring path_w = str2wstr(path);
+			HANDLE h;
+
+			h = CreateFileW(path_w.c_str(), GENERIC_READ|GENERIC_WRITE, /*dwShareMode=*/0, /*lpSecurityAttributes=*/NULL, /*dwCreationDisposition=*/OPEN_EXISTING, /*dwFlagsAndAttributes=*/0, /*hTemplateFile=*/NULL);
+			if (h == INVALID_HANDLE_VALUE) {
+				log_error("CreateFileW failed: %s\n", get_last_error_str().c_str());
+				goto cleanup_path;
+			}
+
+			server = std::make_shared<HandleRpcServer>(path, h, h);
+
+cleanup_path:
+			;
+#else
+			struct sockaddr_un addr;
+			addr.sun_family = AF_UNIX;
+			strncpy(addr.sun_path, path.c_str(), sizeof(addr.sun_path) - 1);
+
+			int fd = socket(AF_UNIX, SOCK_STREAM, 0);
+			if (fd == -1) {
+				log_error("socket failed: %s\n", strerror(errno));
+				goto cleanup_path;
+			}
+
+			if (connect(fd, (struct sockaddr *)&addr, sizeof(addr)) != 0) {
+				log_error("connect failed: %s\n", strerror(errno));
+				goto cleanup_path;
+			}
+
+			server = std::make_shared<FdRpcServer>(path, fd, fd);
+			fd = -1;
+
+cleanup_path:
+			if (fd != -1) close(fd);
+#endif
+		}
+
+		if (!server)
+			log_cmd_error("Failed to connect to RPC frontend.\n");
+
+		for (auto &module_name : server->get_module_names()) {
+			log("Linking module `%s'.\n", module_name.c_str());
+			RpcModule *module = new RpcModule;
+			module->name = "$abstract\\" + module_name;
+			module->server = server;
+			design->add(module);
+		}
+	}
+} RpcFrontend;
+
+YOSYS_NAMESPACE_END
diff --git a/libs/json11/json11.cpp b/libs/json11/json11.cpp
new file mode 100644
index 000000000..549463d71
--- /dev/null
+++ b/libs/json11/json11.cpp
@@ -0,0 +1,788 @@
+/* Copyright (c) 2013 Dropbox, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "json11.hpp"
+#include <cassert>
+#include <cmath>
+#include <cstdlib>
+#include <cstdio>
+#include <limits>
+
+namespace json11 {
+
+static const int max_depth = 200;
+
+using std::string;
+using std::vector;
+using std::map;
+using std::make_shared;
+using std::initializer_list;
+using std::move;
+
+/* Helper for representing null - just a do-nothing struct, plus comparison
+ * operators so the helpers in JsonValue work. We can't use nullptr_t because
+ * it may not be orderable.
+ */
+struct NullStruct {
+    bool operator==(NullStruct) const { return true; }
+    bool operator<(NullStruct) const { return false; }
+};
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Serialization
+ */
+
+static void dump(NullStruct, string &out) {
+    out += "null";
+}
+
+static void dump(double value, string &out) {
+    if (std::isfinite(value)) {
+        char buf[32];
+        snprintf(buf, sizeof buf, "%.17g", value);
+        out += buf;
+    } else {
+        out += "null";
+    }
+}
+
+static void dump(int value, string &out) {
+    char buf[32];
+    snprintf(buf, sizeof buf, "%d", value);
+    out += buf;
+}
+
+static void dump(bool value, string &out) {
+    out += value ? "true" : "false";
+}
+
+static void dump(const string &value, string &out) {
+    out += '"';
+    for (size_t i = 0; i < value.length(); i++) {
+        const char ch = value[i];
+        if (ch == '\\') {
+            out += "\\\\";
+        } else if (ch == '"') {
+            out += "\\\"";
+        } else if (ch == '\b') {
+            out += "\\b";
+        } else if (ch == '\f') {
+            out += "\\f";
+        } else if (ch == '\n') {
+            out += "\\n";
+        } else if (ch == '\r') {
+            out += "\\r";
+        } else if (ch == '\t') {
+            out += "\\t";
+        } else if (static_cast<uint8_t>(ch) <= 0x1f) {
+            char buf[8];
+            snprintf(buf, sizeof buf, "\\u%04x", ch);
+            out += buf;
+        } else if (static_cast<uint8_t>(ch) == 0xe2 && static_cast<uint8_t>(value[i+1]) == 0x80
+                   && static_cast<uint8_t>(value[i+2]) == 0xa8) {
+            out += "\\u2028";
+            i += 2;
+        } else if (static_cast<uint8_t>(ch) == 0xe2 && static_cast<uint8_t>(value[i+1]) == 0x80
+                   && static_cast<uint8_t>(value[i+2]) == 0xa9) {
+            out += "\\u2029";
+            i += 2;
+        } else {
+            out += ch;
+        }
+    }
+    out += '"';
+}
+
+static void dump(const Json::array &values, string &out) {
+    bool first = true;
+    out += "[";
+    for (const auto &value : values) {
+        if (!first)
+            out += ", ";
+        value.dump(out);
+        first = false;
+    }
+    out += "]";
+}
+
+static void dump(const Json::object &values, string &out) {
+    bool first = true;
+    out += "{";
+    for (const auto &kv : values) {
+        if (!first)
+            out += ", ";
+        dump(kv.first, out);
+        out += ": ";
+        kv.second.dump(out);
+        first = false;
+    }
+    out += "}";
+}
+
+void Json::dump(string &out) const {
+    m_ptr->dump(out);
+}
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Value wrappers
+ */
+
+template <Json::Type tag, typename T>
+class Value : public JsonValue {
+protected:
+
+    // Constructors
+    explicit Value(const T &value) : m_value(value) {}
+    explicit Value(T &&value)      : m_value(move(value)) {}
+
+    // Get type tag
+    Json::Type type() const override {
+        return tag;
+    }
+
+    // Comparisons
+    bool equals(const JsonValue * other) const override {
+        return m_value == static_cast<const Value<tag, T> *>(other)->m_value;
+    }
+    bool less(const JsonValue * other) const override {
+        return m_value < static_cast<const Value<tag, T> *>(other)->m_value;
+    }
+
+    const T m_value;
+    void dump(string &out) const override { json11::dump(m_value, out); }
+};
+
+class JsonDouble final : public Value<Json::NUMBER, double> {
+    double number_value() const override { return m_value; }
+    int int_value() const override { return static_cast<int>(m_value); }
+    bool equals(const JsonValue * other) const override { return m_value == other->number_value(); }
+    bool less(const JsonValue * other)   const override { return m_value <  other->number_value(); }
+public:
+    explicit JsonDouble(double value) : Value(value) {}
+};
+
+class JsonInt final : public Value<Json::NUMBER, int> {
+    double number_value() const override { return m_value; }
+    int int_value() const override { return m_value; }
+    bool equals(const JsonValue * other) const override { return m_value == other->number_value(); }
+    bool less(const JsonValue * other)   const override { return m_value <  other->number_value(); }
+public:
+    explicit JsonInt(int value) : Value(value) {}
+};
+
+class JsonBoolean final : public Value<Json::BOOL, bool> {
+    bool bool_value() const override { return m_value; }
+public:
+    explicit JsonBoolean(bool value) : Value(value) {}
+};
+
+class JsonString final : public Value<Json::STRING, string> {
+    const string &string_value() const override { return m_value; }
+public:
+    explicit JsonString(const string &value) : Value(value) {}
+    explicit JsonString(string &&value)      : Value(move(value)) {}
+};
+
+class JsonArray final : public Value<Json::ARRAY, Json::array> {
+    const Json::array &array_items() const override { return m_value; }
+    const Json & operator[](size_t i) const override;
+public:
+    explicit JsonArray(const Json::array &value) : Value(value) {}
+    explicit JsonArray(Json::array &&value)      : Value(move(value)) {}
+};
+
+class JsonObject final : public Value<Json::OBJECT, Json::object> {
+    const Json::object &object_items() const override { return m_value; }
+    const Json & operator[](const string &key) const override;
+public:
+    explicit JsonObject(const Json::object &value) : Value(value) {}
+    explicit JsonObject(Json::object &&value)      : Value(move(value)) {}
+};
+
+class JsonNull final : public Value<Json::NUL, NullStruct> {
+public:
+    JsonNull() : Value({}) {}
+};
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Static globals - static-init-safe
+ */
+struct Statics {
+    const std::shared_ptr<JsonValue> null = make_shared<JsonNull>();
+    const std::shared_ptr<JsonValue> t = make_shared<JsonBoolean>(true);
+    const std::shared_ptr<JsonValue> f = make_shared<JsonBoolean>(false);
+    const string empty_string;
+    const vector<Json> empty_vector;
+    const map<string, Json> empty_map;
+    Statics() {}
+};
+
+static const Statics & statics() {
+    static const Statics s {};
+    return s;
+}
+
+static const Json & static_null() {
+    // This has to be separate, not in Statics, because Json() accesses statics().null.
+    static const Json json_null;
+    return json_null;
+}
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Constructors
+ */
+
+Json::Json() noexcept                  : m_ptr(statics().null) {}
+Json::Json(std::nullptr_t) noexcept    : m_ptr(statics().null) {}
+Json::Json(double value)               : m_ptr(make_shared<JsonDouble>(value)) {}
+Json::Json(int value)                  : m_ptr(make_shared<JsonInt>(value)) {}
+Json::Json(bool value)                 : m_ptr(value ? statics().t : statics().f) {}
+Json::Json(const string &value)        : m_ptr(make_shared<JsonString>(value)) {}
+Json::Json(string &&value)             : m_ptr(make_shared<JsonString>(move(value))) {}
+Json::Json(const char * value)         : m_ptr(make_shared<JsonString>(value)) {}
+Json::Json(const Json::array &values)  : m_ptr(make_shared<JsonArray>(values)) {}
+Json::Json(Json::array &&values)       : m_ptr(make_shared<JsonArray>(move(values))) {}
+Json::Json(const Json::object &values) : m_ptr(make_shared<JsonObject>(values)) {}
+Json::Json(Json::object &&values)      : m_ptr(make_shared<JsonObject>(move(values))) {}
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Accessors
+ */
+
+Json::Type Json::type()                           const { return m_ptr->type();         }
+double Json::number_value()                       const { return m_ptr->number_value(); }
+int Json::int_value()                             const { return m_ptr->int_value();    }
+bool Json::bool_value()                           const { return m_ptr->bool_value();   }
+const string & Json::string_value()               const { return m_ptr->string_value(); }
+const vector<Json> & Json::array_items()          const { return m_ptr->array_items();  }
+const map<string, Json> & Json::object_items()    const { return m_ptr->object_items(); }
+const Json & Json::operator[] (size_t i)          const { return (*m_ptr)[i];           }
+const Json & Json::operator[] (const string &key) const { return (*m_ptr)[key];         }
+
+double                    JsonValue::number_value()              const { return 0; }
+int                       JsonValue::int_value()                 const { return 0; }
+bool                      JsonValue::bool_value()                const { return false; }
+const string &            JsonValue::string_value()              const { return statics().empty_string; }
+const vector<Json> &      JsonValue::array_items()               const { return statics().empty_vector; }
+const map<string, Json> & JsonValue::object_items()              const { return statics().empty_map; }
+const Json &              JsonValue::operator[] (size_t)         const { return static_null(); }
+const Json &              JsonValue::operator[] (const string &) const { return static_null(); }
+
+const Json & JsonObject::operator[] (const string &key) const {
+    auto iter = m_value.find(key);
+    return (iter == m_value.end()) ? static_null() : iter->second;
+}
+const Json & JsonArray::operator[] (size_t i) const {
+    if (i >= m_value.size()) return static_null();
+    else return m_value[i];
+}
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Comparison
+ */
+
+bool Json::operator== (const Json &other) const {
+    if (m_ptr == other.m_ptr)
+        return true;
+    if (m_ptr->type() != other.m_ptr->type())
+        return false;
+
+    return m_ptr->equals(other.m_ptr.get());
+}
+
+bool Json::operator< (const Json &other) const {
+    if (m_ptr == other.m_ptr)
+        return false;
+    if (m_ptr->type() != other.m_ptr->type())
+        return m_ptr->type() < other.m_ptr->type();
+
+    return m_ptr->less(other.m_ptr.get());
+}
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Parsing
+ */
+
+/* esc(c)
+ *
+ * Format char c suitable for printing in an error message.
+ */
+static inline string esc(char c) {
+    char buf[12];
+    if (static_cast<uint8_t>(c) >= 0x20 && static_cast<uint8_t>(c) <= 0x7f) {
+        snprintf(buf, sizeof buf, "'%c' (%d)", c, c);
+    } else {
+        snprintf(buf, sizeof buf, "(%d)", c);
+    }
+    return string(buf);
+}
+
+static inline bool in_range(long x, long lower, long upper) {
+    return (x >= lower && x <= upper);
+}
+
+namespace {
+/* JsonParser
+ *
+ * Object that tracks all state of an in-progress parse.
+ */
+struct JsonParser final {
+
+    /* State
+     */
+    const string &str;
+    size_t i;
+    string &err;
+    bool failed;
+    const JsonParse strategy;
+
+    /* fail(msg, err_ret = Json())
+     *
+     * Mark this parse as failed.
+     */
+    Json fail(string &&msg) {
+        return fail(move(msg), Json());
+    }
+
+    template <typename T>
+    T fail(string &&msg, const T err_ret) {
+        if (!failed)
+            err = std::move(msg);
+        failed = true;
+        return err_ret;
+    }
+
+    /* consume_whitespace()
+     *
+     * Advance until the current character is non-whitespace.
+     */
+    void consume_whitespace() {
+        while (str[i] == ' ' || str[i] == '\r' || str[i] == '\n' || str[i] == '\t')
+            i++;
+    }
+
+    /* consume_comment()
+     *
+     * Advance comments (c-style inline and multiline).
+     */
+    bool consume_comment() {
+      bool comment_found = false;
+      if (str[i] == '/') {
+        i++;
+        if (i == str.size())
+          return fail("unexpected end of input after start of comment", false);
+        if (str[i] == '/') { // inline comment
+          i++;
+          // advance until next line, or end of input
+          while (i < str.size() && str[i] != '\n') {
+            i++;
+          }
+          comment_found = true;
+        }
+        else if (str[i] == '*') { // multiline comment
+          i++;
+          if (i > str.size()-2)
+            return fail("unexpected end of input inside multi-line comment", false);
+          // advance until closing tokens
+          while (!(str[i] == '*' && str[i+1] == '/')) {
+            i++;
+            if (i > str.size()-2)
+              return fail(
+                "unexpected end of input inside multi-line comment", false);
+          }
+          i += 2;
+          comment_found = true;
+        }
+        else
+          return fail("malformed comment", false);
+      }
+      return comment_found;
+    }
+
+    /* consume_garbage()
+     *
+     * Advance until the current character is non-whitespace and non-comment.
+     */
+    void consume_garbage() {
+      consume_whitespace();
+      if(strategy == JsonParse::COMMENTS) {
+        bool comment_found = false;
+        do {
+          comment_found = consume_comment();
+          if (failed) return;
+          consume_whitespace();
+        }
+        while(comment_found);
+      }
+    }
+
+    /* get_next_token()
+     *
+     * Return the next non-whitespace character. If the end of the input is reached,
+     * flag an error and return 0.
+     */
+    char get_next_token() {
+        consume_garbage();
+        if (failed) return static_cast<char>(0);
+        if (i == str.size())
+            return fail("unexpected end of input", static_cast<char>(0));
+
+        return str[i++];
+    }
+
+    /* encode_utf8(pt, out)
+     *
+     * Encode pt as UTF-8 and add it to out.
+     */
+    void encode_utf8(long pt, string & out) {
+        if (pt < 0)
+            return;
+
+        if (pt < 0x80) {
+            out += static_cast<char>(pt);
+        } else if (pt < 0x800) {
+            out += static_cast<char>((pt >> 6) | 0xC0);
+            out += static_cast<char>((pt & 0x3F) | 0x80);
+        } else if (pt < 0x10000) {
+            out += static_cast<char>((pt >> 12) | 0xE0);
+            out += static_cast<char>(((pt >> 6) & 0x3F) | 0x80);
+            out += static_cast<char>((pt & 0x3F) | 0x80);
+        } else {
+            out += static_cast<char>((pt >> 18) | 0xF0);
+            out += static_cast<char>(((pt >> 12) & 0x3F) | 0x80);
+            out += static_cast<char>(((pt >> 6) & 0x3F) | 0x80);
+            out += static_cast<char>((pt & 0x3F) | 0x80);
+        }
+    }
+
+    /* parse_string()
+     *
+     * Parse a string, starting at the current position.
+     */
+    string parse_string() {
+        string out;
+        long last_escaped_codepoint = -1;
+        while (true) {
+            if (i == str.size())
+                return fail("unexpected end of input in string", "");
+
+            char ch = str[i++];
+
+            if (ch == '"') {
+                encode_utf8(last_escaped_codepoint, out);
+                return out;
+            }
+
+            if (in_range(ch, 0, 0x1f))
+                return fail("unescaped " + esc(ch) + " in string", "");
+
+            // The usual case: non-escaped characters
+            if (ch != '\\') {
+                encode_utf8(last_escaped_codepoint, out);
+                last_escaped_codepoint = -1;
+                out += ch;
+                continue;
+            }
+
+            // Handle escapes
+            if (i == str.size())
+                return fail("unexpected end of input in string", "");
+
+            ch = str[i++];
+
+            if (ch == 'u') {
+                // Extract 4-byte escape sequence
+                string esc = str.substr(i, 4);
+                // Explicitly check length of the substring. The following loop
+                // relies on std::string returning the terminating NUL when
+                // accessing str[length]. Checking here reduces brittleness.
+                if (esc.length() < 4) {
+                    return fail("bad \\u escape: " + esc, "");
+                }
+                for (size_t j = 0; j < 4; j++) {
+                    if (!in_range(esc[j], 'a', 'f') && !in_range(esc[j], 'A', 'F')
+                            && !in_range(esc[j], '0', '9'))
+                        return fail("bad \\u escape: " + esc, "");
+                }
+
+                long codepoint = strtol(esc.data(), nullptr, 16);
+
+                // JSON specifies that characters outside the BMP shall be encoded as a pair
+                // of 4-hex-digit \u escapes encoding their surrogate pair components. Check
+                // whether we're in the middle of such a beast: the previous codepoint was an
+                // escaped lead (high) surrogate, and this is a trail (low) surrogate.
+                if (in_range(last_escaped_codepoint, 0xD800, 0xDBFF)
+                        && in_range(codepoint, 0xDC00, 0xDFFF)) {
+                    // Reassemble the two surrogate pairs into one astral-plane character, per
+                    // the UTF-16 algorithm.
+                    encode_utf8((((last_escaped_codepoint - 0xD800) << 10)
+                                 | (codepoint - 0xDC00)) + 0x10000, out);
+                    last_escaped_codepoint = -1;
+                } else {
+                    encode_utf8(last_escaped_codepoint, out);
+                    last_escaped_codepoint = codepoint;
+                }
+
+                i += 4;
+                continue;
+            }
+
+            encode_utf8(last_escaped_codepoint, out);
+            last_escaped_codepoint = -1;
+
+            if (ch == 'b') {
+                out += '\b';
+            } else if (ch == 'f') {
+                out += '\f';
+            } else if (ch == 'n') {
+                out += '\n';
+            } else if (ch == 'r') {
+                out += '\r';
+            } else if (ch == 't') {
+                out += '\t';
+            } else if (ch == '"' || ch == '\\' || ch == '/') {
+                out += ch;
+            } else {
+                return fail("invalid escape character " + esc(ch), "");
+            }
+        }
+    }
+
+    /* parse_number()
+     *
+     * Parse a double.
+     */
+    Json parse_number() {
+        size_t start_pos = i;
+
+        if (str[i] == '-')
+            i++;
+
+        // Integer part
+        if (str[i] == '0') {
+            i++;
+            if (in_range(str[i], '0', '9'))
+                return fail("leading 0s not permitted in numbers");
+        } else if (in_range(str[i], '1', '9')) {
+            i++;
+            while (in_range(str[i], '0', '9'))
+                i++;
+        } else {
+            return fail("invalid " + esc(str[i]) + " in number");
+        }
+
+        if (str[i] != '.' && str[i] != 'e' && str[i] != 'E'
+                && (i - start_pos) <= static_cast<size_t>(std::numeric_limits<int>::digits10)) {
+            return std::atoi(str.c_str() + start_pos);
+        }
+
+        // Decimal part
+        if (str[i] == '.') {
+            i++;
+            if (!in_range(str[i], '0', '9'))
+                return fail("at least one digit required in fractional part");
+
+            while (in_range(str[i], '0', '9'))
+                i++;
+        }
+
+        // Exponent part
+        if (str[i] == 'e' || str[i] == 'E') {
+            i++;
+
+            if (str[i] == '+' || str[i] == '-')
+                i++;
+
+            if (!in_range(str[i], '0', '9'))
+                return fail("at least one digit required in exponent");
+
+            while (in_range(str[i], '0', '9'))
+                i++;
+        }
+
+        return std::strtod(str.c_str() + start_pos, nullptr);
+    }
+
+    /* expect(str, res)
+     *
+     * Expect that 'str' starts at the character that was just read. If it does, advance
+     * the input and return res. If not, flag an error.
+     */
+    Json expect(const string &expected, Json res) {
+        assert(i != 0);
+        i--;
+        if (str.compare(i, expected.length(), expected) == 0) {
+            i += expected.length();
+            return res;
+        } else {
+            return fail("parse error: expected " + expected + ", got " + str.substr(i, expected.length()));
+        }
+    }
+
+    /* parse_json()
+     *
+     * Parse a JSON object.
+     */
+    Json parse_json(int depth) {
+        if (depth > max_depth) {
+            return fail("exceeded maximum nesting depth");
+        }
+
+        char ch = get_next_token();
+        if (failed)
+            return Json();
+
+        if (ch == '-' || (ch >= '0' && ch <= '9')) {
+            i--;
+            return parse_number();
+        }
+
+        if (ch == 't')
+            return expect("true", true);
+
+        if (ch == 'f')
+            return expect("false", false);
+
+        if (ch == 'n')
+            return expect("null", Json());
+
+        if (ch == '"')
+            return parse_string();
+
+        if (ch == '{') {
+            map<string, Json> data;
+            ch = get_next_token();
+            if (ch == '}')
+                return data;
+
+            while (1) {
+                if (ch != '"')
+                    return fail("expected '\"' in object, got " + esc(ch));
+
+                string key = parse_string();
+                if (failed)
+                    return Json();
+
+                ch = get_next_token();
+                if (ch != ':')
+                    return fail("expected ':' in object, got " + esc(ch));
+
+                data[std::move(key)] = parse_json(depth + 1);
+                if (failed)
+                    return Json();
+
+                ch = get_next_token();
+                if (ch == '}')
+                    break;
+                if (ch != ',')
+                    return fail("expected ',' in object, got " + esc(ch));
+
+                ch = get_next_token();
+            }
+            return data;
+        }
+
+        if (ch == '[') {
+            vector<Json> data;
+            ch = get_next_token();
+            if (ch == ']')
+                return data;
+
+            while (1) {
+                i--;
+                data.push_back(parse_json(depth + 1));
+                if (failed)
+                    return Json();
+
+                ch = get_next_token();
+                if (ch == ']')
+                    break;
+                if (ch != ',')
+                    return fail("expected ',' in list, got " + esc(ch));
+
+                ch = get_next_token();
+                (void)ch;
+            }
+            return data;
+        }
+
+        return fail("expected value, got " + esc(ch));
+    }
+};
+}//namespace {
+
+Json Json::parse(const string &in, string &err, JsonParse strategy) {
+    JsonParser parser { in, 0, err, false, strategy };
+    Json result = parser.parse_json(0);
+
+    // Check for any trailing garbage
+    parser.consume_garbage();
+    if (parser.failed)
+        return Json();
+    if (parser.i != in.size())
+        return parser.fail("unexpected trailing " + esc(in[parser.i]));
+
+    return result;
+}
+
+// Documented in json11.hpp
+vector<Json> Json::parse_multi(const string &in,
+                               std::string::size_type &parser_stop_pos,
+                               string &err,
+                               JsonParse strategy) {
+    JsonParser parser { in, 0, err, false, strategy };
+    parser_stop_pos = 0;
+    vector<Json> json_vec;
+    while (parser.i != in.size() && !parser.failed) {
+        json_vec.push_back(parser.parse_json(0));
+        if (parser.failed)
+            break;
+
+        // Check for another object
+        parser.consume_garbage();
+        if (parser.failed)
+            break;
+        parser_stop_pos = parser.i;
+    }
+    return json_vec;
+}
+
+/* * * * * * * * * * * * * * * * * * * *
+ * Shape-checking
+ */
+
+bool Json::has_shape(const shape & types, string & err) const {
+    if (!is_object()) {
+        err = "expected JSON object, got " + dump();
+        return false;
+    }
+
+    for (auto & item : types) {
+        if ((*this)[item.first].type() != item.second) {
+            err = "bad type for " + item.first + " in " + dump();
+            return false;
+        }
+    }
+
+    return true;
+}
+
+} // namespace json11
diff --git a/libs/json11/json11.hpp b/libs/json11/json11.hpp
new file mode 100644
index 000000000..0c47d0509
--- /dev/null
+++ b/libs/json11/json11.hpp
@@ -0,0 +1,232 @@
+/* json11
+ *
+ * json11 is a tiny JSON library for C++11, providing JSON parsing and serialization.
+ *
+ * The core object provided by the library is json11::Json. A Json object represents any JSON
+ * value: null, bool, number (int or double), string (std::string), array (std::vector), or
+ * object (std::map).
+ *
+ * Json objects act like values: they can be assigned, copied, moved, compared for equality or
+ * order, etc. There are also helper methods Json::dump, to serialize a Json to a string, and
+ * Json::parse (static) to parse a std::string as a Json object.
+ *
+ * Internally, the various types of Json object are represented by the JsonValue class
+ * hierarchy.
+ *
+ * A note on numbers - JSON specifies the syntax of number formatting but not its semantics,
+ * so some JSON implementations distinguish between integers and floating-point numbers, while
+ * some don't. In json11, we choose the latter. Because some JSON implementations (namely
+ * Javascript itself) treat all numbers as the same type, distinguishing the two leads
+ * to JSON that will be *silently* changed by a round-trip through those implementations.
+ * Dangerous! To avoid that risk, json11 stores all numbers as double internally, but also
+ * provides integer helpers.
+ *
+ * Fortunately, double-precision IEEE754 ('double') can precisely store any integer in the
+ * range +/-2^53, which includes every 'int' on most systems. (Timestamps often use int64
+ * or long long to avoid the Y2038K problem; a double storing microseconds since some epoch
+ * will be exact for +/- 275 years.)
+ */
+
+/* Copyright (c) 2013 Dropbox, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#pragma once
+
+#include <string>
+#include <vector>
+#include <map>
+#include <memory>
+#include <initializer_list>
+
+#ifdef _MSC_VER
+    #if _MSC_VER <= 1800 // VS 2013
+        #ifndef noexcept
+            #define noexcept throw()
+        #endif
+
+        #ifndef snprintf
+            #define snprintf _snprintf_s
+        #endif
+    #endif
+#endif
+
+namespace json11 {
+
+enum JsonParse {
+    STANDARD, COMMENTS
+};
+
+class JsonValue;
+
+class Json final {
+public:
+    // Types
+    enum Type {
+        NUL, NUMBER, BOOL, STRING, ARRAY, OBJECT
+    };
+
+    // Array and object typedefs
+    typedef std::vector<Json> array;
+    typedef std::map<std::string, Json> object;
+
+    // Constructors for the various types of JSON value.
+    Json() noexcept;                // NUL
+    Json(std::nullptr_t) noexcept;  // NUL
+    Json(double value);             // NUMBER
+    Json(int value);                // NUMBER
+    Json(bool value);               // BOOL
+    Json(const std::string &value); // STRING
+    Json(std::string &&value);      // STRING
+    Json(const char * value);       // STRING
+    Json(const array &values);      // ARRAY
+    Json(array &&values);           // ARRAY
+    Json(const object &values);     // OBJECT
+    Json(object &&values);          // OBJECT
+
+    // Implicit constructor: anything with a to_json() function.
+    template <class T, class = decltype(&T::to_json)>
+    Json(const T & t) : Json(t.to_json()) {}
+
+    // Implicit constructor: map-like objects (std::map, std::unordered_map, etc)
+    template <class M, typename std::enable_if<
+        std::is_constructible<std::string, decltype(std::declval<M>().begin()->first)>::value
+        && std::is_constructible<Json, decltype(std::declval<M>().begin()->second)>::value,
+            int>::type = 0>
+    Json(const M & m) : Json(object(m.begin(), m.end())) {}
+
+    // Implicit constructor: vector-like objects (std::list, std::vector, std::set, etc)
+    template <class V, typename std::enable_if<
+        std::is_constructible<Json, decltype(*std::declval<V>().begin())>::value,
+            int>::type = 0>
+    Json(const V & v) : Json(array(v.begin(), v.end())) {}
+
+    // This prevents Json(some_pointer) from accidentally producing a bool. Use
+    // Json(bool(some_pointer)) if that behavior is desired.
+    Json(void *) = delete;
+
+    // Accessors
+    Type type() const;
+
+    bool is_null()   const { return type() == NUL; }
+    bool is_number() const { return type() == NUMBER; }
+    bool is_bool()   const { return type() == BOOL; }
+    bool is_string() const { return type() == STRING; }
+    bool is_array()  const { return type() == ARRAY; }
+    bool is_object() const { return type() == OBJECT; }
+
+    // Return the enclosed value if this is a number, 0 otherwise. Note that json11 does not
+    // distinguish between integer and non-integer numbers - number_value() and int_value()
+    // can both be applied to a NUMBER-typed object.
+    double number_value() const;
+    int int_value() const;
+
+    // Return the enclosed value if this is a boolean, false otherwise.
+    bool bool_value() const;
+    // Return the enclosed string if this is a string, "" otherwise.
+    const std::string &string_value() const;
+    // Return the enclosed std::vector if this is an array, or an empty vector otherwise.
+    const array &array_items() const;
+    // Return the enclosed std::map if this is an object, or an empty map otherwise.
+    const object &object_items() const;
+
+    // Return a reference to arr[i] if this is an array, Json() otherwise.
+    const Json & operator[](size_t i) const;
+    // Return a reference to obj[key] if this is an object, Json() otherwise.
+    const Json & operator[](const std::string &key) const;
+
+    // Serialize.
+    void dump(std::string &out) const;
+    std::string dump() const {
+        std::string out;
+        dump(out);
+        return out;
+    }
+
+    // Parse. If parse fails, return Json() and assign an error message to err.
+    static Json parse(const std::string & in,
+                      std::string & err,
+                      JsonParse strategy = JsonParse::STANDARD);
+    static Json parse(const char * in,
+                      std::string & err,
+                      JsonParse strategy = JsonParse::STANDARD) {
+        if (in) {
+            return parse(std::string(in), err, strategy);
+        } else {
+            err = "null input";
+            return nullptr;
+        }
+    }
+    // Parse multiple objects, concatenated or separated by whitespace
+    static std::vector<Json> parse_multi(
+        const std::string & in,
+        std::string::size_type & parser_stop_pos,
+        std::string & err,
+        JsonParse strategy = JsonParse::STANDARD);
+
+    static inline std::vector<Json> parse_multi(
+        const std::string & in,
+        std::string & err,
+        JsonParse strategy = JsonParse::STANDARD) {
+        std::string::size_type parser_stop_pos;
+        return parse_multi(in, parser_stop_pos, err, strategy);
+    }
+
+    bool operator== (const Json &rhs) const;
+    bool operator<  (const Json &rhs) const;
+    bool operator!= (const Json &rhs) const { return !(*this == rhs); }
+    bool operator<= (const Json &rhs) const { return !(rhs < *this); }
+    bool operator>  (const Json &rhs) const { return  (rhs < *this); }
+    bool operator>= (const Json &rhs) const { return !(*this < rhs); }
+
+    /* has_shape(types, err)
+     *
+     * Return true if this is a JSON object and, for each item in types, has a field of
+     * the given type. If not, return false and set err to a descriptive message.
+     */
+    typedef std::initializer_list<std::pair<std::string, Type>> shape;
+    bool has_shape(const shape & types, std::string & err) const;
+
+private:
+    std::shared_ptr<JsonValue> m_ptr;
+};
+
+// Internal class hierarchy - JsonValue objects are not exposed to users of this API.
+class JsonValue {
+protected:
+    friend class Json;
+    friend class JsonInt;
+    friend class JsonDouble;
+    virtual Json::Type type() const = 0;
+    virtual bool equals(const JsonValue * other) const = 0;
+    virtual bool less(const JsonValue * other) const = 0;
+    virtual void dump(std::string &out) const = 0;
+    virtual double number_value() const;
+    virtual int int_value() const;
+    virtual bool bool_value() const;
+    virtual const std::string &string_value() const;
+    virtual const Json::array &array_items() const;
+    virtual const Json &operator[](size_t i) const;
+    virtual const Json::object &object_items() const;
+    virtual const Json &operator[](const std::string &key) const;
+    virtual ~JsonValue() {}
+};
+
+} // namespace json11
diff --git a/tests/rpc/.gitignore b/tests/rpc/.gitignore
new file mode 100644
index 000000000..397b4a762
--- /dev/null
+++ b/tests/rpc/.gitignore
@@ -0,0 +1 @@
+*.log
diff --git a/tests/rpc/design.v b/tests/rpc/design.v
new file mode 100644
index 000000000..80f1dac1a
--- /dev/null
+++ b/tests/rpc/design.v
@@ -0,0 +1,8 @@
+module top(input [3:0] i, output [3:0] o);
+	python_inv #(
+	  .width(4)
+	) inv (
+		.i(i),
+		.o(o),
+	);
+endmodule
diff --git a/tests/rpc/exec.ys b/tests/rpc/exec.ys
new file mode 100644
index 000000000..b46009fb9
--- /dev/null
+++ b/tests/rpc/exec.ys
@@ -0,0 +1,5 @@
+connect_rpc -exec python3 frontend.py stdio
+read_verilog design.v
+hierarchy -top top
+flatten
+select -assert-count 1 t:$neg
diff --git a/tests/rpc/frontend.py b/tests/rpc/frontend.py
new file mode 100644
index 000000000..eff41738a
--- /dev/null
+++ b/tests/rpc/frontend.py
@@ -0,0 +1,126 @@
+def modules():
+	return ["python_inv"]
+
+def derive(module, parameters):
+	assert module == r"python_inv"
+	if parameters.keys() != {r"\width"}:
+		raise ValueError("Invalid parameters")
+	return "ilang", r"""
+module \impl
+	wire width {width:d} input 1 \i
+	wire width {width:d} output 2 \o
+	cell $neg $0
+		parameter \A_SIGNED 1'0
+		parameter \A_WIDTH 32'{width:b}
+		parameter \Y_WIDTH 32'{width:b}
+		connect \A \i
+		connect \Y \o
+	end
+end
+module \python_inv
+	wire width {width:d} input 1 \i
+	wire width {width:d} output 2 \o
+	cell \impl $0
+		connect \i \i
+		connect \o \o
+	end
+end
+""".format(width=parameters[r"\width"])
+
+# ----------------------------------------------------------------------------
+
+import json
+import argparse
+import sys, socket, os
+try:
+	import msvcrt, win32pipe, win32file
+except ImportError:
+	msvcrt = win32pipe = win32file = None
+
+def map_parameter(parameter):
+	if parameter["type"] == "unsigned":
+		return int(parameter["value"], 2)
+	if parameter["type"] == "signed":
+		width = len(parameter["value"])
+		value = int(parameter["value"], 2)
+		if value & (1 << (width - 1)):
+			value = -((1 << width) - value)
+		return value
+	if parameter["type"] == "string":
+		return parameter["value"]
+	if parameter["type"] == "real":
+		return float(parameter["value"])
+
+def call(input_json):
+	input = json.loads(input_json)
+	if input["method"] == "modules":
+		return json.dumps({"modules": modules()})
+	if input["method"] == "derive":
+		try:
+			frontend, source = derive(input["module"],
+				{name: map_parameter(value) for name, value in input["parameters"].items()})
+			return json.dumps({"frontend": frontend, "source": source})
+		except ValueError as e:
+			return json.dumps({"error": str(e)})
+
+def main():
+	parser = argparse.ArgumentParser()
+	modes = parser.add_subparsers(dest="mode")
+	mode_stdio = modes.add_parser("stdio")
+	if os.name == "posix":
+		mode_path = modes.add_parser("unix-socket")
+	if os.name == "nt":
+		mode_path = modes.add_parser("named-pipe")
+	mode_path.add_argument("path")
+	args = parser.parse_args()
+
+	if args.mode == "stdio":
+		while True:
+			input = sys.stdin.readline()
+			if not input: break
+			sys.stdout.write(call(input) + "\n")
+			sys.stdout.flush()
+
+	if args.mode == "unix-socket":
+		sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+		sock.bind(args.path)
+		try:
+			sock.listen(1)
+			conn, addr = sock.accept()
+			file = conn.makefile("rw")
+			while True:
+				input = file.readline()
+				if not input: break
+				file.write(call(input) + "\n")
+				file.flush()
+		finally:
+			sock.close()
+			os.unlink(args.path)
+
+	if args.mode == "named-pipe":
+		pipe = win32pipe.CreateNamedPipe(args.path, win32pipe.PIPE_ACCESS_DUPLEX,
+		    win32pipe.PIPE_TYPE_BYTE|win32pipe.PIPE_READMODE_BYTE|win32pipe.PIPE_WAIT,
+		    1, 4096, 4096, 0, None)
+		win32pipe.ConnectNamedPipe(pipe, None)
+		try:
+			while True:
+				input = b""
+				while not input.endswith(b"\n"):
+					result, data = win32file.ReadFile(pipe, 4096)
+					assert result == 0
+					input += data
+					assert not b"\n" in input or input.endswith(b"\n")
+				output = (call(input.decode("utf-8")) + "\n").encode("utf-8")
+				length = len(output)
+				while length > 0:
+					result, done = win32file.WriteFile(pipe, output)
+					assert result == 0
+					length -= done
+		except win32file.error as e:
+			if e.args[0] == 109: # ERROR_BROKEN_PIPE
+				pass
+			else:
+				raise
+
+if __name__ == "__main__":
+	main()
diff --git a/tests/rpc/run-test.sh b/tests/rpc/run-test.sh
new file mode 100755
index 000000000..44ce7e674
--- /dev/null
+++ b/tests/rpc/run-test.sh
@@ -0,0 +1,6 @@
+#!/bin/bash
+set -e
+for x in *.ys; do
+  echo "Running $x.."
+  ../../yosys -ql ${x%.ys}.log $x
+done
diff --git a/tests/rpc/unix.ys b/tests/rpc/unix.ys
new file mode 100644
index 000000000..cc7ec14ab
--- /dev/null
+++ b/tests/rpc/unix.ys
@@ -0,0 +1,6 @@
+!python3 frontend.py unix-socket frontend.sock & sleep 0.1
+connect_rpc -path frontend.sock
+read_verilog design.v
+hierarchy -top top
+flatten
+select -assert-count 1 t:$neg