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

[Sean Christopherson <seanjc@google.com>]

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)
 {