bool cpuid_is_supported(void)
{
- int ret = 0;
+ /* The following assembly code uses EAX as the return value,
+ * but we store the value of EAX into ret since GCC uses EAX
+ * as the return register for every C function. That's a double
+ * operation, but there's no other way to do this unless doing this
+ * function entirely in assembly. */
+
+ /* This check is to make sure that the compiler is actually compiling
+ * for 64-bit.
+ *
+ * The compiler can be 32-bit and the system 64-bit so the
+ * following would be true:
+ * #if defined(__x86_64) ...
+ */
+
+#if UINTPTR_MAX == 0xffffffffffffffff
+#define ASM_PUSHF "pushfq\n\t"
+#define ASM_POPF "popfq\n\t"
+#define ASM_PUSHEAX "pushq %%rax\n\t"
+#define ASM_POPEAX "popq %%rax\n\t"
+#define ASM_PUSHECX "popq %%rcx\n\t"
+#elif UINTPTR_MAX == 0xffffffff
+#define ASM_PUSHF "pushfl\n\t"
+#define ASM_POPF "popfl\n\t"
+#define ASM_PUSHEAX "pushl %%eax\n\t"
+#define ASM_POPEAX "popl %%eax\n\t"
+#define ASM_PUSHECX "popl %%ecx\n\t"
+#endif
+ int ret = 0;
asm volatile(
- "pushfl\n\t"
- "popl %%eax\n\t"
+ ASM_PUSHF
+ ASM_POPEAX
"movl %%eax, %%ecx\n\t"
"xorl $0x200000, %%eax\n\t"
- "pushl %%eax\n\t"
- "popfl\n\t"
-
- "pushfl\n\t"
- "popl %%eax\n\t"
+ ASM_PUSHEAX
+ ASM_POPF
+ ASM_PUSHF
+ ASM_POPEAX
"xorl %%ecx, %%eax\n\t"
"shrl $21, %%eax\n\t"
"andl $1, %%eax\n\t"
- "pushl %%ecx\n\t"
- "popfl\n\t"
-
+ ASM_PUSHECX
+ ASM_POPF
: "=a" (ret)
);
+#undef ASM_PUSHF
+#undef ASM_POPF
+#undef ASM_PUSHEAX
+#undef ASM_POPEAX
+#undef ASM_PUSHECX
+
return !!ret;
}