[S] Change in coreboot[main]: x86/include/arch/cpuid.h: Fix inline assembly

[Felix Held (Code Review)]

Felix Held has submitted this change. ( https://review.coreboot.org/c/coreboot/+/78192?usp=email )

(

1 is the latest approved patch-set.
No files were changed between the latest approved patch-set and the submitted one.
 )Change subject: x86/include/arch/cpuid.h: Fix inline assembly
......................................................................

x86/include/arch/cpuid.h: Fix inline assembly

In the cpuid helper functions eax is always written to
by the cpuid instruction, so add it to the output clobbered list.

This prevents GCC from generating code with undefined behaviour
when the function is inlined.

Test: Verified that the generated assembly is sane and runtime
      tests showed no "strange" behaviour when calling cpuid
      functions.

Change-Id: I5dc0bb620184a355716b9c8d4206d55554b41ab9
Signed-off-by: Patrick Rudolph 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/78192
Reviewed-by: Felix Held 
Tested-by: build bot (Jenkins) 
Reviewed-by: Krystian Hebel 
Reviewed-by: Paul Menzel 
---
M src/arch/x86/include/arch/cpuid.h
1 file changed, 9 insertions(+), 12 deletions(-)

Approvals:
  Felix Held: Looks good to me, but someone else must approve
  Krystian Hebel: Looks good to me, approved
  build bot (Jenkins): Verified
  Paul Menzel: Looks good to me, but someone else must approve

diff --git a/src/arch/x86/include/arch/cpuid.h b/src/arch/x86/include/arch/cpuid.h
index 70a5beb..b2780be 100644
--- a/src/arch/x86/include/arch/cpuid.h
+++ b/src/arch/x86/include/arch/cpuid.h
@@ -56,39 +56,36 @@
    return eax;
 }

-static inline uint32_t cpuid_ebx(const uint32_t eax)
+static inline uint32_t cpuid_ebx(uint32_t eax)
 {
    uint32_t ebx;

asm volatile(
    	"cpuid;"
-		: "=b" (ebx)
-		: "a" (eax)
-		: "ecx", "edx");
+		: "=b" (ebx), "+a" (eax)
+		:: "ecx", "edx");
    return ebx;
 }

-static inline uint32_t cpuid_ecx(const uint32_t eax)
+static inline uint32_t cpuid_ecx(uint32_t eax)
 {
    uint32_t ecx;

asm volatile(
    	"cpuid;"
-		: "=c" (ecx)
-		: "a" (eax)
-		: "ebx", "edx");
+		: "=c" (ecx), "+a" (eax)
+		:: "ebx", "edx");
    return ecx;
 }

-static inline uint32_t cpuid_edx(const uint32_t eax)
+static inline uint32_t cpuid_edx(uint32_t eax)
 {
    uint32_t edx;

asm volatile(
    	"cpuid;"
-		: "=d" (edx)
-		: "a" (eax)
-		: "ebx", "ecx");
+		: "=d" (edx), "+a" (eax)
+		:: "ebx", "ecx");
    return edx;
 }