Re: [Libguestfs] libldm crashes in a linux-sandbox context
On Fri. 16 juin 2023 at 16:34, Richard W.M. Jones <rjones(a)redhat.com> wrote:
(...)
> Last thing, the segfault on ldmtool [1] still seems a valid
issue.
> Even if I now do have a workaround for my problem, that segfault might
> be worth a bit more investigation.
Yes that does look like a real problem. Does it crash if you just run
ldmtool as a normal command, nothing to do with libguestfs? Might be
a good idea to try to get a stack trace of the crash.
The fact is that it only crashes with the UUID 65534 in the qemu VM. I
am not sure what command line is passed to ldmtool for this crash to
occur.
I can help to gather information, but my biggest issue is that I do
not know how to interact with the VM under /tmp/.guestfs-1001/
[ 0.777352] ldmtool[164]: segfault at 0 ip 0000563a225cd6a5 sp
00007ffe54965a60 error 4 in ldmtool[563a225cb000+3000]
^^^^ ^^^^^^^^^^^^^^^^^^^
This smells like a NULL pointer dereference. The instruction pointer
being 563a225cd6a5, I installed libguestfs-tools-dbgsym and tried a:
addr2line -e /usr/bin/ldmtool 564a892506a5
Results:
??:0
Without conviction, I also tried in GDB:
$ gdb /usr/bin/ldmtool
(...)
Reading symbols from /usr/bin/ldmtool...
Reading symbols from
/usr/lib/debug/.build-id/21/37b4a64903ebe427c242be08b8d496ba570583.debug...
(gdb) info line *0x564a892506a5
No line number information available for address 0x564a892506a5
Debug symbols are correctly installed but impossible to convert that
instruction pointer into a line number. It is as if the ldmtool on my
host and the ldmtool in the qemu VM were from a different build. I
tried to mount /tmp/.guestfs-1001/appliance.d/root but that disk image
did not contain ldmtool.
I am not sure how to generate a stack trace or a core dump within that
qemu VM. If you can tell me how to get an interactive prompt (or any
other guidance) I can try to collect more information.
Yours sincerely,
Vincent Mailhol