Hi Shuah,
On 2/7/2022 10:00 AM, Shuah Khan wrote:
This will work fine on newer versions of gcc/clang. However this could fail when mainline kselftest is used on stable releases on test rings and so on, especially if they have older versions of gcc/clang.
Indeed. It thus seems that kselftest has a minimal required version for gcc/clang that is not the current mainline minimal version but the minimal version of the oldest supported stable kernel, which is v4.9.
__cpuid_count() was added to gcc in commit: cb0dee885cb30b4e9beeef070cf000baa7d09abe and thus available since gcc 4.4.
Looking at Documentation/Changes or later Documentation/process/changes.rst kernels v4.9 and v4.14 have the minimal required version of gcc of 3.2. So this change would encounter an issue if mainline kselftest is used to test a v4.9 or v4.14 kernel on a system that only supports its minimal gcc.
Kernel v4.19 moved the gcc minimal required version to 4.6 that does contain this macro.
There does not seem to be a minimum required version of clang/LLVM in v4.19. The first time I see a minimal version for Clang/LLVM for a stable kernel is in kernel v5.10 with Clang/LLVM minimal version 10.0.1 and from what I can tell the __cpuid_count() macro was added to Clang/LLVM in version 3.4.0 (commit 4dcb5dbb53ea4fbeab48bc6bc3c4d392361dabc1).
We will have to find a solution for this. Instead of deleting the local define, let's keep it under ifndef __cpuid_count
/usr/lib/gcc/x86_64-linux-gnu/11/include/cpuid.h
#define __cpuid_count(level, count, a, b, c, d) \ __asm__ __volatile__ ("cpuid\n\t" \ : "=a" (a), "=b" (b), "=c" (c), "=d" (d) \ : "0" (level), "2" (count))
Will do. I see that gcc obtained the volatile qualifier in v11.1 so I can use the most recent macro as you have here.
Reinette