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&gt; 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