Catching SIGSEGVs as they happen

Periodically situations arise where applications will write to memory that isn’t mapped into their address space. On UNIX systems, this results in a SIGSEGV signal being sent to the offending process. If for some reason you can’t get a core file, you can run the application under the control of the catchsegv utility. The following example shows the results that are displayed when a SIGSEGV signal is received, and the program was run under the control of the catchsegv script:

$ catchsegv ./coreme 10000000

Calling malloc() to allocate 10000000 bytes of heap space
*** Segmentation fault
Register dump:

 EAX: fffffffc   EBX: bff12634   ECX: bff12634   EDX: 00bd3ff4
 ESI: bff12634   EDI: 00000000   EBP: bff12648   ESP: bff12488

 EIP: 0034a402   EFLAGS: 00200246

 CS: 0073   DS: 007b   ES: 007b   FS: 0000   GS: 0033   SS: 007b

 Trap: 00000000   Error: 00000000   OldMask: 00000000
 ESP/signal: bff12488   CR2: 00000000

Backtrace:
/lib/libSegFault.so[0x3d512f]
??:0(??)[0x34a420]
??:0(main)[0x8048453]
/lib/libc.so.6(__libc_start_main+0xdc)[0xab0f2c]
??:0(_start)[0x8048361]

Memory map:

0034a000-0034b000 r-xp 0034a000 00:00 0 [vdso]
003d3000-003d6000 r-xp 00000000 08:01 1426324 /lib/libSegFault.so
003d6000-003d7000 r-xp 00002000 08:01 1426324 /lib/libSegFault.so
003d7000-003d8000 rwxp 00003000 08:01 1426324 /lib/libSegFault.so
00a47000-00a52000 r-xp 00000000 08:01 1427470 /lib/libgcc_s-4.1.1-20070105.so.1
00a52000-00a53000 rwxp 0000a000 08:01 1427470 /lib/libgcc_s-4.1.1-20070105.so.1
00a7e000-00a97000 r-xp 00000000 08:01 1427446 /lib/ld-2.5.so
00a97000-00a98000 r-xp 00018000 08:01 1427446 /lib/ld-2.5.so
00a98000-00a99000 rwxp 00019000 08:01 1427446 /lib/ld-2.5.so
00a9b000-00bd2000 r-xp 00000000 08:01 1427447 /lib/libc-2.5.so
00bd2000-00bd4000 r-xp 00137000 08:01 1427447 /lib/libc-2.5.so
00bd4000-00bd5000 rwxp 00139000 08:01 1427447 /lib/libc-2.5.so
00bd5000-00bd8000 rwxp 00bd5000 00:00 0
08048000-08049000 r-xp 00000000 08:03 1442166 /home/matty/coreme
08049000-0804a000 rw-p 00000000 08:03 1442166 /home/matty/coreme
095bd000-095e2000 rw-p 095bd000 00:00 0
b75f4000-b7f7f000 rw-p b75f4000 00:00 0
b7f8c000-b7f8e000 rw-p b7f8c000 00:00 0
bfefe000-bff13000 rw-p bfefe000 00:00 0 [stack]

This is a nifty utility, and can be useful for viewing the environment of a process at the time the segmentation violation occurred.

Leave a Reply

Your email address will not be published. Required fields are marked *