I was looking through alerts this morning and found this one that
happened in GitHub's infrastructure a few days ago. Usually these are
memory corruption issues (and get dealt with via a separate process),
but this was a legitimate SEGV in the merge-tree builtin.
The backtrace is as follows:
(gdb) bt
#0 oid_to_hex (oid=0x4) at hex.c:164
#1 0x000056234188aba3 in real_merge (prefix=0x0, branch2=<optimized out>, branch1=<optimized out>, o=0x7ffd3fc4cd60) at builtin/merge-tree.c:528
#2 cmd_merge_tree (argc=<optimized out>, argv=0x7ffd3fc4d7c0, prefix=0x0) at builtin/merge-tree.c:658
#3 0x000056234181ffe9 in run_builtin (argv=0x7ffd3fc4d7c0, argc=8, p=0x562341d5c788 <commands+1896>) at git.c:465
#4 handle_builtin (argc=8, argv=0x7ffd3fc4d7c0) at git.c:724
#5 0x000056234182117f in run_argv (argv=0x7ffd3fc4d4f0, argcp=0x7ffd3fc4d4fc) at git.c:792
#6 cmd_main (argc=<optimized out>, argv=<optimized out>) at git.c:923
#7 0x000056234181fb80 in main (argc=11, argv=0x7ffd3fc4d7a8) at common-main.c:59
and it looks like the result's tree object is left NULL, which we then
produce a SEGV on when trying to pass `&NULL->object.oid` to
`oid_to_hex()`:
(gdb) up
#1 0x000056234188aba3 in real_merge (prefix=0x0, branch2=<optimized out>,
branch1=<optimized out>, o=0x7ffd3fc4cd60) at builtin/merge-tree.c:528
528 builtin/merge-tree.c: No such file or directory.
(gdb) p result->tree
$1 = (struct tree *) 0x0
I haven't looked too hard at these paths (nor do I have a useful
reproduction, since the top-level `argv` array is optimized out). But I
figured I'd share it here in case this was obvious to either one of you.
Thanks in advance for taking a look, and let me know if there's any
information you need from me in order to debug it further.
Thanks,
Taylor
