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.

diff --git a/src/ChangeLog b/src/ChangeLog
index 6ef5746daa2c4b8d24ed6b9438a64969a441e0a4..1f0781fef108834954412cd526adc19f03638f09 100644 (file)
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,13 @@
+2015-02-25  Paul Eggert  <eggert@cs.ucla.edu>
+
+       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  <jan.h.d@swipnet.se>
 
        * nsfns.m (Fx_frame_geometry): New function.

diff --git a/src/emacs.c b/src/emacs.c
index 4a6d6badf286a2b90edb0e6d58702d9c7f52aa10..c2b698ba50be2b2a3aa6167a7c067780ce72f914 100644 (file)
--- 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 a2bda96192f5300ef8870e9bec4f01b50d2361fe..cb361ec2dc517ff59a9d7500ed2df8da43e14a36 100644 (file)
--- 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)
 {