(gdb) b XS_MyMod_myfunc
Breakpoint 2 at 0x2a97e2fdc0: file MyMod.c, line xxx.
(gdb) ...

Program received signal SIGSEGV, Segmentation fault.
Perl_sv_unref_flags (sv=0x833a80, flags=1) at sv.c:7972
7972        if (SvREFCNT(rv) != 1 || (flags & SV_IMMEDIATE_UNREF))
(gdb) backtrace
#0  Perl_sv_unref_flags (sv=0x833a80, flags=1) at sv.c:7972
#1  0x00000000004ae782 in Perl_leave_scope (base=47) at scope.c:925
#2  0x00000000004b407e in Perl_pp_return () at pp_ctl.c:1912
#3  0x000000000048659e in Perl_runops_standard () at run.c:38
#4  0x000000000043ca28 in perl_run (my_perl=Variable "my_perl" is not available.
) at perl.c:1934
#5  0x000000000041c66d in main (argc=3, argv=0x7fbffff868, env=Variable "env" is not available.
) at perlmain.c:98
(gdb)