tools/libxc: Fix x86_32 build breakage in previous changeset.

Signed-off-by: Keir Fraser <keir@xen.org>
xen-unstable changeset:   24345:491c3ebf1d37
xen-unstable date:        Fri Dec 02 08:40:02 2011 -0800


tools/x86_64: Fix cpuid() inline asm to not clobber stack's red zone

Pushing stuff onto the stack on x86-64 when we do not specify
-mno-red-zone is unsafe. Since the complicated asm is due to register
pressure on i386, we simply implement an all-new simpler alternative
for x86-64.

Signed-off-by: Keir Fraser <keir@xen.org>
Acked-by: Jan Beulich <jbeulich@novell.com>
xen-unstable changeset:   24344:72f4e4cb7440
xen-unstable date:        Fri Dec 02 06:31:14 2011 -0800

2 files changed, 18 insertions, 15 deletions

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index 09c1bf0613..2c042318af 100644
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -41,23 +41,23 @@ static int hypervisor_is_64bit(int xc)
 static void cpuid(const unsigned int *input, unsigned int *regs)
 {
     unsigned int count = (input[1] == XEN_CPUID_INPUT_UNUSED) ? 0 : input[1];
-    asm (
 #ifdef __i386__
+    /* Use the stack to avoid reg constraint failures with some gcc flags */
+    asm (
         "push %%ebx; push %%edx\n\t"
-#else
-        "push %%rbx; push %%rdx\n\t"
-#endif
         "cpuid\n\t"
         "mov %%ebx,4(%4)\n\t"
         "mov %%edx,12(%4)\n\t"
-#ifdef __i386__
         "pop %%edx; pop %%ebx\n\t"
-#else
-        "pop %%rdx; pop %%rbx\n\t"
-#endif
         : "=a" (regs[0]), "=c" (regs[2])
         : "0" (input[0]), "1" (count), "S" (regs)
         : "memory" );
+#else
+    asm (
+        "cpuid"
+        : "=a" (regs[0]), "=b" (regs[1]), "=c" (regs[2]), "=d" (regs[3])
+        : "0" (input[0]), "2" (count) );
+#endif
 }
 
 /* Get the manufacturer brand name of the host processor. */
diff --git a/tools/misc/xen-detect.c b/tools/misc/xen-detect.c
index 565f27adb4..787b5da90d 100644
--- a/tools/misc/xen-detect.c
+++ b/tools/misc/xen-detect.c
@@ -35,18 +35,21 @@
 
 static void cpuid(uint32_t idx, uint32_t *regs, int pv_context)
 {
-    asm volatile (
 #ifdef __i386__
-#define R(x) "%%e"#x"x"
-#else
-#define R(x) "%%r"#x"x"
-#endif
-        "push "R(a)"; push "R(b)"; push "R(c)"; push "R(d)"\n\t"
+    /* Use the stack to avoid reg constraint failures with some gcc flags */
+    asm volatile (
+        "push %%eax; push %%ebx; push %%ecx; push %%edx\n\t"
         "test %1,%1 ; jz 1f ; ud2a ; .ascii \"xen\" ; 1: cpuid\n\t"
         "mov %%eax,(%2); mov %%ebx,4(%2)\n\t"
         "mov %%ecx,8(%2); mov %%edx,12(%2)\n\t"
-        "pop "R(d)"; pop "R(c)"; pop "R(b)"; pop "R(a)"\n\t"
+        "pop %%edx; pop %%ecx; pop %%ebx; pop %%eax\n\t"
         : : "a" (idx), "c" (pv_context), "S" (regs) : "memory" );
+#else
+    asm volatile (
+        "test %5,%5 ; jz 1f ; ud2a ; .ascii \"xen\" ; 1: cpuid\n\t"
+        : "=a" (regs[0]), "=b" (regs[1]), "=c" (regs[2]), "=d" (regs[3])
+        : "0" (idx), "1" (pv_context), "2" (0) );
+#endif
 }
 
 static int check_for_xen(int pv_context)