On Wed, Aug 29, 2012 at 9:21 AM, Ian Lance Taylor <i...@google.com> wrote: > On Wed, Aug 29, 2012 at 12:43 AM, Janne Blomqvist > <blomqvist.ja...@gmail.com> wrote: >> On Wed, Aug 29, 2012 at 10:22 AM, Ian Lance Taylor <i...@google.com> wrote: >>> I've spent the last couple of days working on a stack backtrace library. >>> >>> It uses the GCC unwind interface to collect a stack trace, and parses >>> DWARF debug info to get file/line/function information. >> [snip] >>> I expect to use this code not just for GCC proper, but also for libgo >>> (currently libgo uses Go code to parse DWARF, but that is not very >>> satisfactory as that code is only available if it has been imported into >>> the program). So I put it under a BSD license, although that is open >>> for discussion. Also in case it finds more uses elsewhere I wrote it in >>> reasonably portable C rather than C++. >>> >>> >>> Does this seem like something we could usefully add to GCC? Does >>> anybody see any big problems with it? >> >> I haven't looked at the code, but if it is async-signal-safe it could >> be interesting for gfortran. Currently in libgfortran we have a >> backtracing routine, originally written by FX Coudert IIRC, since >> rewritten by yours truly a few times, that uses _Unwind_Backtrace() >> from libgcc and then pipes the output via addr2line, if found. Since >> it's invoked from a signal handler when the program (user program, not >> the compiler!) crashes, it needs to be async-signal-safe. AFAIK the >> current implementation *should* fulfill that requirement. But >> something that would be async-signal-safe and won't need addr2line to >> get symbolic info would be a nice improvement, in particular since >> addr2line doesn't work on OSX, and all that piping stuff doesn't work >> on Windows. > > I believe the unwinder proper is async signal safe--it just uses > _Unwind_Backtrace. > > The DWARF reader calls malloc and is therefore not async-signal safe. > It would be difficult to write an efficient DWARF reader that does not > allocate any memory, and I'm not aware of any way to allocate memory > that is defined to be async-signal safe. That said, as far as I know > mmap is async-signal safe in practice if not in theory, so one > approach would be to do memory allocation using mmap. >
Using mmap instead of malloc is a good idea. It should fix: http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24724 -- H.J.
