Re: [PATCH] KVM: selftests: Guard execinfo.h inclusion for non-glibc builds

[Hisam Mehboob <hisamshar@gmail.com>]

On 4/1/26 19:01, Sean Christopherson wrote:
> On Tue, Mar 31, 2026, Shuah Khan wrote:
>> On 3/25/26 12:47, Hisam Mehboob wrote:
>>> On 3/25/26 23:03, Shuah Khan wrote:
>>>> On 3/24/26 12:02, Shuah Khan wrote:
>>>>> On 3/18/26 18:08, Hisam Mehboob wrote:
>>>>>> The backtrace() function and execinfo.h are GNU extensions available
>>>>>> in glibc but not in non-glibc C libraries such as musl. Building KVM
>>>>>> selftests with musl-gcc fails with:
>>>>>>
>>>>>>     lib/assert.c:9:10: fatal error: execinfo.h: No such file or directory
>>>>>>
>>>>>> Guard the inclusion of execinfo.h under #ifdef __GLIBC__, and wrap
>>>>>> all backtrace() usage under the same guard with a fallback message
>>>>>> for non-glibc builds indicating that stack traces are not available.
>>>>>>
>>>>>> Unlike the approach of adding a weak stub for backtrace(), this
>>>>>> explicitly handles the non-glibc case rather than silently providing
>>>>>> an empty implementation.
>>>>>>
>>>>>> Link: https://lore.kernel.org/kvm/20250829142556.72577-7- aqibaf@amazon.com/
>>>>>>
>>>>>> Suggested-by: Aqib Faruqui <aqibaf@amazon.com>
>>>>>> Signed-off-by: Hisam Mehboob <hisamshar@gmail.com>
>>>>>> ---
>>>>>>    tools/testing/selftests/kvm/lib/assert.c | 7 +++++++
>>>>>>    1 file changed, 7 insertions(+)
>>>>>>
>>>>>> diff --git a/tools/testing/selftests/kvm/lib/assert.c b/tools/ testing/selftests/kvm/lib/assert.c
>>>>>> index b49690658c60..3442b80c37c1 100644
>>>>>> --- a/tools/testing/selftests/kvm/lib/assert.c
>>>>>> +++ b/tools/testing/selftests/kvm/lib/assert.c
>>>>>> @@ -6,7 +6,9 @@
>>>>>>     */
>>>>>>    #include "test_util.h"
>>>>>> +#ifdef __GLIBC__
>>>>>>    #include <execinfo.h>
>>>>>> +#endif
>>>>>> Is __GLIBC__ defined in musl-gcc? Looks like that is the case with the
>>>>> error?
>>>>
>>>> If __GLIBC__ isn't there you shouldn't see this error because the include
>>>> is in - this error doesn't make sense if __GLIBC__ isn't defined. What
>>>> am I missing?
>>>>
>>>
>>> To clarify the compiler error you mentioned: the error log in the commit
>>> message shows the failure that occurs before this patch is applied. Because
>>> musl-gcc doesn't define __GLIBC__, the original unconditional <execinfo.h>
>>> inclusion causes the build to fail. The #ifdef in my patch was intended to
>>> fix that exact failure.
>>>
>>>> +#ifdef __GLIBC__
>>>>    #include <execinfo.h>
>>>> +#endif
>>>>
>>>> Also check tools/testing/selftests/bpf/test_progs.c - I think backtrace()
>>>> stub needs be defined only for the !__GLIBC__ case
>>>>
>>>
>>> Looking at how bpf/test_progs.c handles it, I agree the weak stub approach
>>> is much cleaner. I will implement it so that it still prints an explicit
>>> warning message when a trace is unavailable.
> 
> I disagree.  _If_ we didn't need the __GLIBC__ #ifdef, then I would be in favor
> of __weak, but since the #ifdeffery is needed, using an #ifdef and a __weak symbol
> is double the ugliness.
> 
> IMO, the way to make this less ugly is to using a single #ifdef and a local stub.
> 
> diff --git a/tools/testing/selftests/kvm/lib/assert.c b/tools/testing/selftests/kvm/lib/assert.c
> index b49690658c60..315175ca49f1 100644
> --- a/tools/testing/selftests/kvm/lib/assert.c
> +++ b/tools/testing/selftests/kvm/lib/assert.c
> @@ -6,11 +6,13 @@
>    */
>   #include "test_util.h"
>   
> -#include <execinfo.h>
>   #include <sys/syscall.h>
>   
>   #include "kselftest.h"
>   
> +#ifdef __GLIBC__
> +#include <execinfo.h>
> +
>   /* Dumps the current stack trace to stderr. */
>   static void __attribute__((noinline)) test_dump_stack(void);
>   static void test_dump_stack(void)
> @@ -57,6 +59,9 @@ static void test_dump_stack(void)
>          system(cmd);
>   #pragma GCC diagnostic pop
>   }
> +#else
> +static void test_dump_stack(void) {}
> +#endif
>   
>   static pid_t _gettid(void)
>   {

Thanks for the suggestion. I will send a v2 implementing this approach.