[Emacs-diffs] master b74db63: Backtrace after malloc arena is corrupted

[Paul Eggert]

branch: master
commit b74db6347cf5cac1ebd4c604fd5691c588fd8e32
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>

    Backtrace after malloc arena is corrupted
    
    Without this change, if the malloc arena is corrupted and then
    'backtrace' is called, the backtrace can crash because 'backtrace'
    calls 'malloc'.  For more, please see:
    https://sourceware.org/ml/libc-alpha/2015-02/msg00678.html
    * emacs.c (main): Initialize tables used by 'backtrace'.
    * sysdep.c (emacs_backtrace): Document the newly used part of the API.
---
 src/ChangeLog |   10 ++++++++++
 src/emacs.c   |    2 ++
 src/sysdep.c  |   12 +++++++++++-
 3 files changed, 23 insertions(+), 1 deletions(-)

diff --git a/src/ChangeLog b/src/ChangeLog
index 6ef5746..1f0781f 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,13 @@
+2015-02-25  Paul Eggert  <address@hidden>
+
+       Backtrace after malloc arena is corrupted
+       Without this change, if the malloc arena is corrupted and then
+       'backtrace' is called, the backtrace can crash because 'backtrace'
+       calls 'malloc'.  For more, please see:
+       https://sourceware.org/ml/libc-alpha/2015-02/msg00678.html
+       * emacs.c (main): Initialize tables used by 'backtrace'.
+       * sysdep.c (emacs_backtrace): Document the newly used part of the API.
+
 2015-02-22  Jan Djärv  <address@hidden>
 
        * nsfns.m (Fx_frame_geometry): New function.
diff --git a/src/emacs.c b/src/emacs.c
index 4a6d6ba..c2b698b 100644
--- a/src/emacs.c
+++ b/src/emacs.c
@@ -884,6 +884,8 @@ main (int argc, char **argv)
 
   clearerr (stdin);
 
+  emacs_backtrace (-1);
+
 #if !defined SYSTEM_MALLOC && !defined HYBRID_MALLOC
   /* Arrange to get warning messages as memory fills up.  */
   memory_warnings (0, malloc_warning);
diff --git a/src/sysdep.c b/src/sysdep.c
index a2bda96..cb361ec 100644
--- a/src/sysdep.c
+++ b/src/sysdep.c
@@ -2147,7 +2147,17 @@ snprintf (char *buf, size_t bufsize, char const *format, 
...)
 /* If a backtrace is available, output the top lines of it to stderr.
    Do not output more than BACKTRACE_LIMIT or BACKTRACE_LIMIT_MAX lines.
    This function may be called from a signal handler, so it should
-   not invoke async-unsafe functions like malloc.  */
+   not invoke async-unsafe functions like malloc.
+
+   If BACKTRACE_LIMIT is -1, initialize tables that 'backtrace' uses
+   but do not output anything.  This avoids some problems that can
+   otherwise occur if the malloc arena is corrupted before 'backtrace'
+   is called, since 'backtrace' may call malloc if the tables are not
+   initialized.
+
+   If the static variable THREAD_BACKTRACE_NPOINTERS is nonzero, a
+   fatal error has occurred in some other thread; generate a thread
+   backtrace instead, ignoring BACKTRACE_LIMIT.  */
 void
 emacs_backtrace (int backtrace_limit)
 {