Bruno Haible <bruno <at> clisp.org> writes: > > are there any platforms where switching to c-stack would cause a > > regression in m4's stack detection abilities if we don't port m4's fallbacks > > for supporting older APIs? > > > > [1]http://git.savannah.gnu.org/gitweb/?p=m4.git;a=blob;f=src/stackovf.c > > Looking at m4's current code requirements: > > - sigvec/SV_ONSTACK is pointless; it was last needed on SunOS4. The only > platform nowadays without sigaction is mingw. > > - sigaltstack is present and works on > Linux, FreeBSD, NetBSD, AIX, HP-UX 11.11, IRIX, OSF/1, Solaris, and > (more or less) MacOS X. > It is not available on > OpenBSD, HP-UX 11.23, Cygwin, mingw, BeOS.
Actually, sigaltstack is in OpenBSD 4.0. I've tested that both m4 and c-stack reported a stack overflow message on OpenBSD 4.0. But with both OpenBSD 4.0 and Linux glibc 2.3.4, I noticed that config.h's HAVE_XSI_STACK_OVERFLOW_HEURISTIC was undefined with c-stack, so it seems like _any_ segv, rather than true overflows, would be reported on those platforms (I guess I'll have to enhance and rerun my tests with an intentional non-overflow segv to verify). Or maybe c-stack.m4's test case is too restrictive. > > - But the most constraining requirement is how to get the fault address: > - 'ip->si_addr' works only on > Linux >= 2.4, HP-UX, OSF/1, Solaris. > (The same code would also work on FreeBSD, NetBSD, OpenBSD if you > were catching SIGBUS in addition to SIGSEGV.) > - The "struct sigcontext *scp, char *addr" code is useless, it never > works. (It would work on FreeBSD if you were catching SIGBUS, not > only SIGSEGV.) > > So m4's current code (approximately) only works on Linux >= 2.4, HP-UX, OSF/1, > Solaris. And these are the same platforms on which 'c-stack' works, I believe. Thanks. I don't feel as worried about swapping over to c-stack, then. And it is always the case that if someone pipes up with a regression (and more importantly, an alternative that will work on their platform), we can revisit the issue at that point. And by using gnulib's c-stack, other projects will also benefit. -- Eric Blake
