[LTP] [PATCH] sigrelse01: Check if signal 34 is available for musl compat

[Petr Vorel]

Hi Florian,

> On 08/08/2025 16.04, Petr Vorel wrote:
> > Hi Florian,

> Hi Petr,

> thanks for your review.

yw, thanks for your work on LTP for musl.

> > > Do not select signal 34 when the test is run using musl. Signal 34 is
> > > used internally by musl as SIGSYNCCALL. Consequently, musl's signal()
> > > will return with an error status and errno set to EINVAL when trying
> > > to setup a signal handler for signal 34, causing the sigrelse01 test
> > > to fail.

> > > Since musl provides no preprocessor macro, we check for the
> > > availability of signal 34 by attempting to setup a signal handler. If
> > > signal() returns SIG_ERR with errno set to EINVAL then we assume the
> > > signal is unavailable. Knowing signal 34 is available with glibc, we
> > > perform this check only if __GLIBC__ is not defined.

> > ...
> > > +++ b/testcases/kernel/syscalls/sigrelse/sigrelse01.c

> > > +#define _GNU_SOURCE

> > Unfortunately +#define _GNU_SOURCE causes test to hang, at least on glibc.

> I don't think it hangs, but takes ages to complete. At least, that is what I
> found.

Yeah, you're more precise :). Nevertheless the result for the patchset remains
=> NACK when runtime drastically changes like this :(.


> > And I see for musl it is necessary to get sighandler_t.
> > Until you fix glibc with _GNU_SOURCE NACK.

> I think I can get rid of the _GNU_SOURCE. IIRC it was just needed to use the
> sighandler_t type. Without _GNU_SOURCE, declaring the return value of
> signal() as void* should also work.

I suspect there is something else going wrong (test should not start magically
using sighold() on glibc), but let's try a workaround.


> > But on glibc it also brought a warning, which means _GNU_SOURCE really switches
> > something on:

> > sigrelse01.c: In function ‘child’:
> > sigrelse01.c:397:33: warning: ‘sighold’ is deprecated: Use the sigprocmask function instead [-Wdeprecated-declarations]
> >    397 |                                 if ((rv = sighold(sig)) != 0) {
> >        |                                 ^~
> > In file included from /usr/include/sys/wait.h:36,
> >                   from sigrelse01.c:104:
> > /usr/include/signal.h:355:12: note: declared here
> >    355 | extern int sighold (int __sig) __THROW
> >        |            ^~~~~~~
> > sigrelse01.c:472:25: warning: ‘sigrelse’ is deprecated: Use the sigprocmask function instead [-Wdeprecated-declarations]
> >    472 |                         if ((rv = sigrelse(sig)) != 0) {
> >        |                         ^~
> > /usr/include/signal.h:359:12: note: declared here
> >    359 | extern int sigrelse (int __sig) __THROW
> >        |            ^~~~~~~~
> > sigrelse01.c: In function ‘timeout’:
> > sigrelse01.c:675:25: warning: unused parameter ‘sig’ [-Wunused-parameter]
> >    675 | static void timeout(int sig)
> >        |                     ~~~~^~~

> > Also this is a very old test, which needs cleanup and rewrite to new LTP API
> > (e.g. remove old unixes, e.g. VAX and get test more reliable). I suppose
> > handling signals with LTP legacy API is broken.

> > > +
> > >   #include <sys/types.h>
> > >   #include <sys/wait.h>
> > >   #include <errno.h>
> > >   #include <fcntl.h>
> > >   #include <signal.h>
> > > +#include <stdbool.h>

> > nit: I would postpone this after conversion this to new LTP API.
> > Script already uses legacy definitions
> > #define TRUE 1
> > #define FALSE 0
> > and on a different place happily returns 0 or 1.
> > Mixing that with <stdbool.h> makes even more mess.

> Agreed.

> I am going send a v2 that does not use _GNU_SOURCE nor stdbool.h after
> checking that it still fixes musl compat for us while not introducing a
> regression on glibc.

+1, please document the reason for a workaround.

If you had more time, the best would be to rewrite the test to the new LTP API.
I bet the problem with _GNU_SOURCE would go away. I don't expect you have more
time, but if you do, here are links:

https://github.com/linux-test-project/ltp/blob/master/doc/old/C-Test-API.asciidoc
https://linux-test-project.readthedocs.io/en/latest/developers/api_c_tests.html
https://linux-test-project.readthedocs.io/en/latest/developers/test_case_tutorial.html

(We are in the middle of a doc transition into readthedocs, IMHO the old doc is
still the best what we have.)

Also, 3 tests even don't compile on musl, here is the current list:
https://github.com/linux-test-project/ltp/blob/master/ci/alpine.sh#L32

Helping to fix them is more than welcome.

Kind regards,
Petr


> - Florian