On Tue, 8 Aug 2023, Maciej W. Rozycki wrote:
> > Looks like GDB is not too happy with the core file I obtained, see below. Is
> > this a known issue with gdb-12.1? gdb-11.x was not faring any better
> > unfortunately. The core dump is attached (hope it makes it to the mailing
> > list).
>
> Sigh. Back in 2017 I fixed numerous issues with MIPS core file handling
> in GDB, which was then well-tested, and I haven't looked at it since. So
> it must be a regression, either in GDB or in the producer (Linux kernel).
>
> I can reproduce it and I'll see if I can debug this. I may ask you for
> the corresponding binary and shared libraries at one point.
>
> NB I note that the core file is ELF32 and does not have the EF_MIPS_ABI2
> flag set in its file header, so it looks like an o32 core file to me.
> Since your subject mentions n32/n64, can you please check what kind of
> binary your `iperf3' is (e.g. `file iperf3', `readelf -h iperf3', etc.)?
I tweaked the core file and set the EF_MIPS_ABI2 flag by hand. This has
let GDB proceed:
[...]
warning: File "/usr/lib/debug/.build-id" has no build-id, file skipped
Core was generated by `iperf3 -c 192.168.254.3'.
Program terminated with signal SIGILL, Illegal instruction.
#0 0x77eb3190 in ?? (
[...]
but this is a partial core file only and I have no corresponding binaries,
so I can't tell more at this stage, i.e. what code there is at 0x77eb3190
(the PC address is suspiciously high in the 32-bit address space BTW, is
that a PIE run with address space randomisation?).
Of course GDB shouldn't have hit an internal error with a broken core
file anyway, it should complain and handle the situation gracefully. But
in any case it's an issue with the Linux kernel producing a core file in
the wrong format.
Is this the most recent Linux kernel version you have obtained this with?
There used to be a bug (regression) in Linux with n32 core files, but I
fixed it also in 2017, with commit 547da673173d ("MIPS: Fix an n32 core
file generation regset support regression"). So if it has stopped working
again, then it's a new regression. Would you be able to bisect it?
Maciej
