2 files changed, 147 insertions, 9 deletions
diff --git a/doc/building/VendorPrimitives.rst b/doc/building/VendorPrimitives.md
index b608c0825..b608c0825 100644
--- a/doc/building/VendorPrimitives.rst
+++ b/doc/building/VendorPrimitives.md
diff --git a/doc/building/index.rst b/doc/building/index.rst
index ea35d19c0..9cdc812f9 100644
--- a/doc/building/index.rst
+++ b/doc/building/index.rst
@@ -3,35 +3,173 @@
 Building GHDL
 #############
 
+GHDL currently supports three supported different backends (code generators): mcode, GCC and LLVM. Here is a short comparison, so that you can choose the one you want to use:
+
+* mcode (an internal code generator)
++ very easy to build
+- but x86_64/i386 only
++ very quick analysis time
++ can analyze very big designs
+- simulation is slower
+- no executable created
+
+* GCC
++ generated code is faster (particularly with -O or -O2)
++ generated code can be debugged (with -g)
++ the output is an executable
++ ported to many platforms (x86, x86_64, powerpc, sparc)
+- analyze can takes time (particularly for big units)
+- build is more complex
+
+* LLVM
++ same advantages of gcc (good generated code, debuggable)
++ easier to build than gcc
+
+As GHDL is written in Ada, you need to use the GNU Ada compiler (GNAT). I recommend to use GNAT GPL from http://libre.adacore.com (free). GHDL was tested with GNAT GPL 2014.  Any later version should work.
+The only other dependency is zlib (On ubuntu/debian, install zlib1g-dev).
+
 .. TODO::
 
   - `./doc/oldmds/BUILD.txt <https://github.com/tgingold/ghdl/blob/master/doc/oldmds/BUILD.txt>`_
   - Directory structure of the main branch [1138: #279]
   - Coverage, `gcov`, is unique to gcc. That specific difference is not explained anywhere. Should be added.
   - @1138 Backtraces optional -patchable-
-
-GCC backend
+  - Very briefly, why is mode faster for analysis and GCC/LLVM for simulation?
+	   
+Mcode backend
 =================
 
-- `./doc/oldmds/gcc/INSTALL <https://github.com/tgingold/ghdl/blob/master/doc/oldmds/gcc/INSTALL>`_
-- `./doc/oldmds/gcc/README <https://github.com/tgingold/ghdl/blob/master/doc/oldmds/gcc/README>`_
 - Linux
 
+This is as simple as:
+
+$ ./configure --prefix=PREFIX
+
+  where PREFIX is the directory for installation
+
+$ make
+
+  This builds the ghdl_mcode executable, which can be used as is.
+
+$ make install
+
+  To install within PREFIX
+
+- Windows MinGW 32/64
+- Windows GNAT GPL (32 only)
+
+.. TODO::
+
+	Note: this was tested with Windows XP SP2 familly edition.
+
+	Note: If you want to create the installer, GHDL should be built on a FAT partition.  NSIS rounds files date to be FAT compliant (seconds are always even) and because GHDL stores dates, the files date must not be modified.
+
+	The Ada95 GNAT compiler (GNAT GPL 2005 is known to work), along with NSIS to create the installer. Then unzip, edit winbuild to use correct path for makensis, and run winbuild. The installer is in the windows directory.
+	   
 LLVM backend 
 =================
 
 - Linux
+
+You need to build and install llvm.  The supported versions are 3.5
+till 3.9, but only debugging is only supported with llvm 3.5
+(Usually llvm also depends on libedit).
+
+First configure ghdl with '--with-llvm-config'
+$ ./configure --with-llvm-config
+
+If llvm-config is not in your path, you can specify it:
+$ ./configure --with-llvm-config=LLVM_INSTALL/bin/llvm-config
+
+If you want to have stack backtraces on errors (like assert failure or
+index of out bounds), you need to configure and build libbacktrace from gcc
+(you don't need to configure gcc), and add to configure:
+  --with-backtrace-lib=/path-to-gcc-build/libbacktrace/.libs/libbacktrace.a
+
+Then build with 'make' and install with 'make install'.
+  
 - Mac OS?
 - Windows MinGW 32/64
-	  
-Mcode backend
+	   
+GCC backend
 =================
 
-- `./doc/oldmds/mcode/README <https://github.com/tgingold/ghdl/blob/master/doc/oldmds/windows/mcode/README>`_
 - Linux
-- Windows GNAT GPL (32 only)
-- Windows MinGW 32/64
 
+You need to download and untar the sources of
+gcc version 4.9 [do not modify this line as this is read by scripts].
+
+First configure ghdl, specify gcc source dir and prefix.
+(replace /usr/local by your prefix directory):
+$ ./configure --with-gcc=/path/to/gcc/source/dir --prefix=/usr/local
+
+Then invoke make to copy ghdl sources in the source dir:
+$ make copy-sources
+
+There are some dependencies for building gcc (gmp, mpfr and mpc). If you have
+not them installed on your system, you can either build them manually or use
+the 'download_prerequisite' script provided in gcc source tree (recommended).
+
+$ cd /path/to/gcc/source/dir
+$ ./contrib/download_prerequisites
+
+Then configure gcc.  The list of --disable configure options could be
+adjusted for your needs.  GHDL don't require all these optional
+libraries and disabling them speed-up the build. Note the prefix
+directory must be the same as the one used to configure ghdl.
+If you have manually built gmp/mpfr/mpc (without using the script
+in contrib) and if you have installed them in a non-standard
+directory, you may need to add --with-gmp=GMP_INSTALL_DIR.
+
+$ mkdir gcc-objs; cd gcc-objs
+$ ../gcc-4.9.3/configure --prefix=/usr/local --enable-languages=c,vhdl \
+  --disable-bootstrap --disable-lto --disable-multilib \
+  --disable-libssp --disable-libgomp --disable-libquadmath
+$ make -j2
+
+Install gcc:
+$ make install
+or if you don't want to install makeinfo:
+$ make install MAKEINFO=true
+
+Build and install vhdl libraries:
+$ cd /path/to/ghdl/source/dir
+$ make ghdllib
+$ make install
+
+- Windows?
+
+.. TODO:
+
+    Since the content of BUILD.txt is moved to the docs, what shall we do with this line? +gcc version 6.3 [do not modify this line as this is read by scripts].
+
+	Note for ppc64 (and AIX ?) platform: the object file format contains an identifier for the source language. Because gcc doesn't know about the VHDL, gcc crashes very early. This could be fixed with a very simple change in gcc/config/rs6000/rs6000.c, function rs6000_output_function_epilogue (as of gcc 4.8):
+       else if (! strcmp (language_string, "GNU Objective-C"))
+        i = 14;
+       else
+-       gcc_unreachable ();
++       i = 0;
+       fprintf (file, "%d,", i);
+
+       /* 8 single bit fields: global linkage (not set for C extern linkage,
+
+	Install file for the binary distribution of GHDL. The binary are installed in /usr/local directory.  You cannot change this default location, unless you set links. You must be root to install this distribution. To install ghdl: `tar -C / -jxvf @TARFILE@.tar.bz2`. Note: you must also have a C compiler and zlib installed.
+
+- Notes for developpers
+
+Developping with the gcc backend:
+Once gcc (with ghdl) has been built once, it is possible to work on ghdl
+sources tree without copying them in gcc tree. Commands are:
+$ make ghdl1-gcc     	     # To build the compiler
+$ make ghdl_gcc		     # To build the driver
+$ make libs.vhdl.local_gcc   # To compile the vhdl libraries
+$ make grt-all		     # To build the ghdl runtime
+$ make grt.links	     # To locally install the ghdl runtime
+
+.. TODO::
+
+	gcc object dir
+	
 Test suites
 =================