[musl] Crash in kill(..., SIGHUP) when using SA_ONSTACK

[Pablo Correa Gomez <pabloyoyoista@postmarketos.org>]

Hi everybody,

I am responsible for musl CI in GNOME's GLib, and we have recently
bumped into a crash that I have been unable to resolve. 

https://gitlab.gnome.org/GNOME/glib/-/commit/137db219a7266300ffde1aa75d781284fb0807cb
introduced in GLib an alternate stack by setting the signal action
SA_ONSTACK if available. However, the tests that were introduced, and
that pass in most other libc's (there's CI for a lot more than just
glibc and musl) crash in my alpine linux edge installation with SIGSEGV
(stack trace below) while doing: kill (getpid(), SIGHUP)

I have verified that not adding SA_ONSTACK fixes the crash. Would
anybody have some pointers of what could possibly be going wrong? If
anybody is really interested, the public issue is
https://gitlab.gnome.org/GNOME/glib/-/issues/3315

Stack trace
------------

Thread 1 "unix" received signal SIGSEGV, Segmentation fault.
0x00007ffff7fa96e8 in __syscall2 (a2=1, a1=17483, n=62) at
./arch/x86_64/syscall_arch.h:21
warning: 21     ./arch/x86_64/syscall_arch.h: No such file or directory
(gdb) bt
#0  0x00007ffff7fa96e8 in __syscall2 (a2=1, a1=17483, n=62) at
./arch/x86_64/syscall_arch.h:21
#1  kill (pid=17483, sig=sig@entry=1) at src/signal/kill.c:6
#2  0x0000555555556e96 in test_signal (signum=signum@entry=1) at
../glib/tests/unix.c:534
#3  0x0000555555557200 in test_signal_alternate_stack (signal=1) at
../glib/tests/unix.c:590
#4  0x00007ffff7e8f364 in test_case_run (path=<optimized out>,
test_run_name=0x55555555d3f0 "/glib-unix/sighup/alternate-stack",
tc=0x55555555db60) at ../glib/gtestutils.c:2988
#5  g_test_run_suite_internal (suite=suite@entry=0x55555555da70,
path=path@entry=0x0) at ../glib/gtestutils.c:3090
#6  0x00007ffff7e8f2db in g_test_run_suite_internal
(suite=suite@entry=0x7ffff7ffee20, path=path@entry=0x0) at
../glib/gtestutils.c:3109
#7  0x00007ffff7e8f2db in g_test_run_suite_internal
(suite=suite@entry=0x7ffff7ffede0, path=path@entry=0x0) at
../glib/gtestutils.c:3109
#8  0x00007ffff7e8f86a in g_test_run_suite
(suite=suite@entry=0x7ffff7ffede0) at ../glib/gtestutils.c:3189
#9  0x00007ffff7e8f8ea in g_test_run () at ../glib/gtestutils.c:2275
#10 0x00005555555561f7 in main (argc=<optimized out>, argv=<optimized
out>) at ../glib/tests/unix.c:910

Best and thanks for your time,
Pablo.