Remove the JIT-ed CPUID hack from mono-hwcap-x86.

A proper workaround for the 32-bit PIC issue exists: Using xchg to
unclobber EBX which is used by the compiler. This means we can just
use inline assembly to issue the instruction, eliminating the hack
where we JIT-compiled a function to do the CPUID.

This patch also makes it so that we use MSVC's __cpuid intrinsic
on both 32-bit and 64-bit x86 since it's available on both.

mono/utils/mono-hwcap-x86.c

@@ -24,63 +24,8 @@
 #include <unistd.h>
 #endif
 
-#if defined(TARGET_X86)
-#include "mono/utils/mono-codeman.h"
-
-typedef void (* CpuidFunc) (int id, int *p_eax, int *p_ebx, int *p_ecx, int *p_edx);
-
-static MonoCodeManager *code_man;
-static CpuidFunc func;
-
-#if defined(__native_client__)
-static const guchar cpuid_impl [] = {
-	0x55,								/* push   %ebp */
-	0x89, 0xe5,							/* mov    %esp, %ebp */
-	0x53,								/* push   %ebx */
-	0x8b, 0x45, 0x08,					/* mov    0x8 (%ebp), %eax */
-	0x0f, 0xa2,							/* cpuid   */
-	0x50,								/* push   %eax */
-	0x8b, 0x45, 0x10,					/* mov    0x10 (%ebp), %eax */
-	0x89, 0x18,							/* mov    %ebx, (%eax) */
-	0x8b, 0x45, 0x14,					/* mov    0x14 (%ebp), %eax */
-	0x89, 0x08,							/* mov    %ecx, (%eax) */
-	0x8b, 0x45, 0x18,					/* mov    0x18 (%ebp), %eax */
-	0x89, 0x10,							/* mov    %edx, (%eax) */
-	0x58,								/* pop    %eax */
-	0x8b, 0x55, 0x0c,					/* mov    0xc (%ebp), %edx */
-	0x89, 0x02,							/* mov    %eax, (%edx) */
-	0x5b,								/* pop    %ebx */
-	0xc9,								/* leave   */
-	0x59, 0x83, 0xe1, 0xe0, 0xff, 0xe1,	/* naclret */
-	0xf4, 0xf4, 0xf4, 0xf4, 0xf4, 0xf4,	/* padding, to provide bundle aligned version */
-	0xf4, 0xf4, 0xf4, 0xf4, 0xf4, 0xf4,
-	0xf4, 0xf4, 0xf4, 0xf4, 0xf4, 0xf4,
-	0xf4, 0xf4, 0xf4, 0xf4, 0xf4, 0xf4,
-	0xf4,
-};
-#else
-static const guchar cpuid_impl [] = {
-	0x55,								/* push   %ebp */
-	0x89, 0xe5,							/* mov    %esp, %ebp */
-	0x53,								/* push   %ebx */
-	0x8b, 0x45, 0x08,					/* mov    0x8 (%ebp), %eax */
-	0x0f, 0xa2,							/* cpuid   */
-	0x50,								/* push   %eax */
-	0x8b, 0x45, 0x10,					/* mov    0x10 (%ebp), %eax */
-	0x89, 0x18,							/* mov    %ebx, (%eax) */
-	0x8b, 0x45, 0x14,					/* mov    0x14 (%ebp), %eax */
-	0x89, 0x08,							/* mov    %ecx, (%eax) */
-	0x8b, 0x45, 0x18,					/* mov    0x18 (%ebp), %eax */
-	0x89, 0x10,							/* mov    %edx, (%eax) */
-	0x58,								/* pop    %eax */
-	0x8b, 0x55, 0x0c,					/* mov    0xc (%ebp), %edx */
-	0x89, 0x02,							/* mov    %eax, (%edx) */
-	0x5b,								/* pop    %ebx */
-	0xc9,								/* leave   */
-	0xc3,								/* ret     */
-};
-#endif
-
+#if defined(_MSC_VER)
+#include <intrin.h>
 #endif
 
 gboolean mono_hwcap_x86_is_xen = FALSE;
@@ -97,13 +42,8 @@ gboolean mono_hwcap_x86_has_sse4a = FALSE;
 static gboolean
 cpuid (int id, int *p_eax, int *p_ebx, int *p_ecx, int *p_edx)
 {
+	/* First, make sure we can use cpuid if we're on 32-bit. */
 #if defined(TARGET_X86)
-
-#if defined(__native_client__)
-	func (id, p_eax, p_ebx, p_ecx, p_edx);
-
-	return TRUE;
-#else
 	gboolean have_cpuid = FALSE;
 
 #if defined(_MSC_VER)
@@ -122,77 +62,60 @@ cpuid (int id, int *p_eax, int *p_ebx, int *p_ecx, int *p_edx)
 	}
 #else
 	__asm__ __volatile__ (
-		"pushfl\n"
-		"popl %%eax\n"
-		"movl %%eax, %%edx\n"
-		"xorl $0x200000, %%eax\n"
-		"pushl %%eax\n"
-		"popfl\n"
-		"pushfl\n"
-		"popl %%eax\n"
-		"xorl %%edx, %%eax\n"
-		"andl $0x200000, %%eax\n"
-		"movl %%eax, %0"
+		"pushfl\n\t"
+		"popl\t%%eax\n\t"
+		"movl\t%%eax, %%edx\n\t"
+		"xorl\t$0x200000, %%eax\n\t"
+		"pushl\t%%eax\n\t"
+		"popfl\n\t"
+		"pushfl\n\t"
+		"popl\t%%eax\n\t"
+		"xorl\t%%edx, %%eax\n\t"
+		"andl\t$0x200000, %%eax\n\t"
+		"movl\t%%eax, %0\n\t"
 		: "=r" (have_cpuid)
 		:
 		: "%eax", "%edx"
 	);
 #endif
 
-	if (have_cpuid) {
-		func (id, p_eax, p_ebx, p_ecx, p_edx);
-
-		return TRUE;
-	}
-
-	return FALSE;
+	if (!have_cpuid)
+		return FALSE;
 #endif
 
-#else
-
+	/* Now issue the actual cpuid instruction. We can use
+	   MSVC's __cpuid on both 32-bit and 64-bit. */
 #if defined(_MSC_VER)
 	int info [4];
 	__cpuid (info, id);
 	*p_eax = info [0];
 	*p_ebx = info [1];
 	*p_ecx = info [2];
 	*p_edx = info [3];
+#elif defined(TARGET_X86)
+	/* This complicated stuff is necessary because EBX
+	   may be used by the compiler in PIC mode. */
+	__asm__ __volatile__ (
+		"xchgl\t%%ebx, %k1\n\t"
+		"cpuid\n\t"
+		"xchgl\t%%ebx, %k1\n\t"
+		: "=a" (*p_eax), "=&r" (*p_ebx), "=c" (*p_ecx), "=d" (*p_edx)
+		: "0" (id)
+	);
 #else
 	__asm__ __volatile__ (
-		"cpuid"
+		"cpuid\n\t"
 		: "=a" (*p_eax), "=b" (*p_ebx), "=c" (*p_ecx), "=d" (*p_edx)
 		: "a" (id)
 	);
 #endif
 
 	return TRUE;
-#endif
 }
 
 void
 mono_hwcap_arch_init (void)
 {
-#if defined(TARGET_X86)
-	code_man = mono_code_manager_new ();
-
-#if defined(__native_client__)
-	gpointer ptr = mono_code_manager_reserve (code_man, sizeof (cpuid_impl));
-	memcpy (ptr, cpuid_impl, sizeof (cpuid_impl));
-	gpointer end_ptr = ptr + sizeof (cpuid_impl);
-
-	guint8 *code = nacl_code_manager_get_dest (code_man, ptr);
-	mono_code_manager_commit (code_man, ptr, sizeof (cpuid_impl), end_ptr - ptr);
-
-	func = (CpuidFunc) code;
-#else
-	gpointer ptr = mono_code_manager_reserve (code_man, sizeof (cpuid_impl));
-	memcpy (ptr, cpuid_impl, sizeof (cpuid_impl));
-
-	func = (CpuidFunc) ptr;
-#endif
-
-#endif
-
 	int eax, ebx, ecx, edx;
 
 	if (cpuid (1, &eax, &ebx, &ecx, &edx)) {
@@ -231,10 +154,6 @@ mono_hwcap_arch_init (void)
 		}
 	}
 
-#if defined(TARGET_X86)
-	mono_code_manager_destroy (code_man);
-#endif
-
 #if defined(HAVE_UNISTD_H)
 	mono_hwcap_x86_is_xen = !access ("/proc/xen", F_OK);
 #endif