From 8b0dc77a621ded75f72486c33f55404ce73f00d7 Mon Sep 17 00:00:00 2001 From: Jake Zimmerman Date: Fri, 10 Jul 2020 12:05:34 -0700 Subject: [PATCH] configure.ac: Bump the size of sigaltstack The RubyVM uses C macro defines to feature detect whether `backtrace(2)` support is available, and if so it includes C level backtraces when the RubyVM itself crashes. But on my machine, C level backtraces from `vm_dump.c` didn't work when using a version of Ruby buillt on the machine, but worked fine when using a version of Ruby built on another machine and copied to my machine. The default autoconf test for backtraces uses a sigaltstack size that is too small, so the SIGSEGV signal handler itself causes a SIGSEGV). I noticed that signal.c uses a larger sigaltstack size: https://github.com/ruby/ruby/blob/v2_6_5/signal.c#L568 The specific variables it looks at: - `HAVE_BACKTRACE` this is a macro defined by autoconf because there is a line in the configure script like `AC_CHECK_FUNCS(backtrace)` (see the autoconf docs for more). - `BROKEN_BACKTRACE` this comes from a custom program that Ruby's configure script runs to attempt to figure out whether actually using backtrace(2) in a real program works. You can see the autoconf program here. It uses sigaltstack and SA_ONSTACK to create a seperate stack for handling signals. The problem was: SIGSTKSZ (which comes from a system header!) was not suggesting a large enough stack size. When checking on an Ubuntu 16.04 box, we found that SIGSTKSZ was 8192 and MINSIGSTKSZ was 2048. --- configure.ac | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/configure.ac b/configure.ac index dc4ab53caa..ae908f7516 100644 --- a/configure.ac +++ b/configure.ac @@ -2948,12 +2948,12 @@ main(void) stack_t ss; struct sigaction sa; - ss.ss_sp = malloc(SIGSTKSZ); + ss.ss_sp = malloc(16*1024); if (ss.ss_sp == NULL) { fprintf(stderr, "cannot allocate memory for sigaltstack\n"); return EXIT_FAILURE; } - ss.ss_size = SIGSTKSZ; + ss.ss_size = 16*1024; ss.ss_flags = 0; if (sigaltstack(&ss, NULL) == -1) { fprintf(stderr, "sigaltstack failed\n");