CODEWITHSUNDEEP
c++gdb
Danny
Danny

Reputation: 2683

gdb stops when using watchpoints (as if ctrl-Z)

I've been using gdb for years but have not seen this behavior before.

To debug a SIGABRT coming from a double free() somewhere in the program, I've set a watch point on the pointer to the buffer. Now when I run the program again, gdb 'stops' as if I pressed ctrl-Z or it received SIGSTOP.

Any idea what's going on there and how do I avoid it?

# gdb --version
GNU gdb (GDB) Red Hat Enterprise Linux 8.2-6.el8
# uname -a
Linux Centos8 4.18.0-147.el8.x86_64 #1 SMP Wed Dec 4 21:51:45 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

The error:

(gdb) run
free(): invalid pointer

Program received signal SIGABRT, Aborted.
0x00007ffff6ad48df in raise () from /lib64/libc.so.6
(gdb) bt
#0  0x00007ffff6ad48df in raise () from /lib64/libc.so.6
#1  0x00007ffff6abecf5 in abort () from /lib64/libc.so.6
#2  0x00007ffff6b17c17 in __libc_message () from /lib64/libc.so.6
#3  0x00007ffff6b1e53c in malloc_printerr () from /lib64/libc.so.6
#4  0x00007ffff6b2210e in free_check.part () from /lib64/libc.so.6
#5  0x00007ffff7bbde99 in MyProgram::parseTSPayload (this=0x6165b0) at MyProgram.cpp:284
...
#8  0x0000000000401b4c in main (argc=6, argv=0x7fffffffea28) at MyProgram.cpp:169
(gdb) f 5
#5  0x00007ffff7bbde99 in MyProgram::parseTSPayload (this=0x6165b0) at MyProgram.cpp:284
284                 delete [] mpPESBuf;

Set watchpoint:

(gdb) watch mpPESBuf
Hardware watchpoint 2: mpPESBuf
(gdb) info watch
Num     Type           Disp Enb Address            What
2       hw watchpoint  keep y                      mpPESBuf

Now when I run the program again, gdb 'stops' as if I pressed ctrl-Z or it received SIGSTOP:

(gdb) run  
The program being debugged has been started already.
Start it from the beginning? (y or n) y
Starting program: MyProgram

[1]+  Stopped                 gdb MyProgram
# fg
gdb MyProgram
Error in re-setting breakpoint 2: No symbol "mpPESBuf" in current context.
Error in re-setting breakpoint 2: No symbol "mpPESBuf" in current context.
Error in re-setting breakpoint 2: No symbol "mpPESBuf" in current context.
warning: Loadable section ".note.gnu.property" outside of ELF segments
warning: Loadable section ".note.gnu.property" outside of ELF segments

[1]+  Stopped                 gdb MyProgram
# fg
gdb MyProgram
Error in re-setting breakpoint 2: No symbol "mpPESBuf" in current context.

[PID 687305] MyProgram Version 1.1-18
Built 2020.11.24-11:43:08.  Launched 2020-11-24 11:56:17.
free(): invalid pointer

Program received signal SIGABRT, Aborted.
0x00007ffff6ad48df in raise () from /lib64/libc.so.6

Upvotes: 0

Views: 238

Answers (1)

Andrew
Andrew

Reputation: 4801

This is a bug in GDB that was fixed with this commit:

https://sourceware.org/legacy-ml/gdb-patches/2019-05/msg00361.html

This commit was in GDB 9, and you are using 8.2. You'll need to update your version of GDB in order to avoid this issue.

Upvotes: 1

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