Call cpuid via inline asm on x86-64, so we can use it with Clang (no

cpuid intrinsic) and older GCC (no cpuid.h before 4.3)

1 files changed, 16 insertions, 2 deletions

diff --git a/src/utils/cpuid.cpp b/src/utils/cpuid.cpp
index 917789f65..c5710d689 100644
--- a/src/utils/cpuid.cpp
+++ b/src/utils/cpuid.cpp
@@ -24,9 +24,9 @@
 #elif defined(BOTAN_BUILD_COMPILER_IS_INTEL)
 
   #include <ia32intrin.h>
-  #define CALL_CPUID(type, out) do { __cpuid(out, type); } while(0);
+  #define CALL_CPUID(type, out) do { __cpuid(out, type); } while(0)
 
-#elif (BOTAN_GCC_VERSION >= 430)
+#elif defined(BOTAN_BUILD_COMPILER_IS_GCC) && (BOTAN_GCC_VERSION >= 430)
 
   // Only available starting in GCC 4.3
   #include <cpuid.h>
@@ -46,6 +46,20 @@ namespace {
 
 }
 
+#elif defined(BOTAN_TARGET_ARCH_IS_X86_64) && \
+   (defined(BOTAN_BUILD_COMPILER_IS_CLANG) || defined(BOTAN_BUILD_COMPILER_IS_GCC))
+
+  /*
+  * We can't safely use this on x86-32 as some 32-bit ABIs use ebx as
+  * a PIC register, and in theory there are some x86-32s still out
+  * there that don't support cpuid at all; it requires strange
+  * contortions to detect them.
+  */
+
+  #define CALL_CPUID(type, out) \
+    asm("cpuid\n\t" : "=a" (out[0]), "=b" (out[1]), "=c" (out[2]), "=d" (out[3]) \
+        : "0" (type))
+
 #else
   #warning "No method of calling CPUID for this compiler"
 #endif