KVM: selftests: Guard execinfo.h inclusion for non-glibc builds

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

Posted by Hisam Mehboob 2 weeks, 4 days ago

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
 #include <sys/syscall.h>
 
 #include "kselftest.h"
@@ -15,6 +17,7 @@
 static void __attribute__((noinline)) test_dump_stack(void);
 static void test_dump_stack(void)
 {
+#ifdef __GLIBC__
 	/*
 	 * Build and run this command:
 	 *
@@ -56,6 +59,10 @@ static void test_dump_stack(void)
 #pragma GCC diagnostic ignored "-Wunused-result"
 	system(cmd);
 #pragma GCC diagnostic pop
+
+#else /* !__GLIBC__ */
+	fputs("  (stack trace not available: compiled without glibc)\n", stderr);
+#endif
 }
 
 static pid_t _gettid(void)
-- 
2.51.0

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

Posted by Shuah Khan 1 week, 5 days ago

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?

Check a couple of things first: did you run "make headers" and
do you have the correct packages installed on your system?

thanks,
-- Shuah

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

Posted by Shuah Khan 1 week, 4 days ago

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?

+#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

thanks,
-- Shuah

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

Posted by Hisam Mehboob 1 week, 4 days ago

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.

If you are okay with this, I will move forward with a v2 patch.

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

Posted by Shuah Khan 5 days, 15 hours ago

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.
> 
> If you are okay with this, I will move forward with a v2 patch.
> 

Ultimately kvm maintainers make the call - send v2 patch

thanks,
-- Shuah

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

Posted by Sean Christopherson 5 days ago

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)
 {