From: Eric Biggers <ebiggers3@gmail.com>
Date: Sat, 22 Aug 2015 16:27:12 +0000 (-0500)
Subject: x86_cpu_features.c: cpuid fix for x86_32 PIC with old GCC versions
X-Git-Tag: v1.8.2~3
X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=719a063c87e3abab99b0fb53ebc80223fbf33123;hp=6bf4bba9f875d1815989a94c39a27f01961d82bb

x86_cpu_features.c: cpuid fix for x86_32 PIC with old GCC versions
---

diff --git a/src/x86_cpu_features.c b/src/x86_cpu_features.c
index f8347575..aab200ff 100644
--- a/src/x86_cpu_features.c
+++ b/src/x86_cpu_features.c
@@ -22,13 +22,23 @@
 
 u32 _x86_cpu_features = 0;
 
+/* With old GCC versions we have to manually save and restore the x86_32 PIC
+ * register (ebx).  See: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=47602  */
+#if defined(__i386__) && defined(__PIC__)
+#  define EBX_CONSTRAINT "=r"
+#else
+#  define EBX_CONSTRAINT "=b"
+#endif
+
 /* Execute the CPUID instruction.  */
 static inline void
-cpuid(u32 leaf, u32 subleaf, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx)
+cpuid(u32 leaf, u32 subleaf, u32 *a, u32 *b, u32 *c, u32 *d)
 {
-	__asm__ ("cpuid"
-		 : "=a" (*eax), "=b" (*ebx), "=c" (*ecx), "=d" (*edx)
-		 : "a" (leaf), "c" (subleaf));
+	__asm__(".ifnc %%ebx, %1; mov  %%ebx, %1; .endif\n"
+		"cpuid                                  \n"
+		".ifnc %%ebx, %1; xchg %%ebx, %1; .endif\n"
+		: "=a" (*a), EBX_CONSTRAINT (*b), "=c" (*c), "=d" (*d)
+		: "a" (leaf), "c" (subleaf));
 }
 
 /* Read an extended control register.  */