3:16 a.m.
This just reminded me of a quick trick on github, we can add a '.patch'
and '.diff' at the end of that url to directly get a patch/diff which we
can wget and apply.
Just shared as I find it very useful :D
Thanks,
Aditya Gupta
>
> >
> > I will update on my findings.
> >
> > Thanks,
> > Aditya Gupta
> >
> > >
> > > Thanks,
> > > Tao Liu
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > >
> > > > Thanks,
> > > > Aditya Gupta
> > > >
> > > > >
> > > > > Thanks,
> > > > > Tao Liu
> > > > >
> > > > >
> > > > > >
> > > > > > Thanks,
> > > > > > Kazu
> > > > > >
> > > > > > On 2024/01/05 16:30, Aditya Gupta wrote:
> > > > > > > The Problem:
> > > > > > > ============
> > > > > > >
> > > > > > > Currently crash is unable to show function arguments
and local variables, as
> > > > > > > gdb can do. And functionality for moving between frames
('up'/'down') is not
> > > > > > > working in crash.
> > > > > > >
> > > > > > > Crash has 'gdb passthroughs' for things gdb can
do, but the gdb passthroughs
> > > > > > > 'bt', 'frame', 'info locals',
'up', 'down' are not working either, due to
> > > > > > > gdb not getting the register values from
`crash_target::fetch_registers`,
> > > > > > > which then uses `machdep->get_cpu_reg`, which is not
implemented for PPC64
> > > > > > >
> > > > > > > Proposed Solution:
> > > > > > > ==================
> > > > > > >
> > > > > > > Fix the gdb passthroughs by implementing
"machdep->get_cpu_reg" for PPC64.
> > > > > > > This way, "gdb mode in crash" will support
this feature for both ELF and
> > > > > > > kdump-compressed vmcore formats, while "gdb"
would only have supported ELF
> > > > > > > format
> > > > > > >
> > > > > > > This way other features of 'gdb', such as
seeing
> > > > > > > backtraces/registers/variables/arguments/local
variables, moving up and
> > > > > > > down stack frames, can be used with any ppc64 vmcore,
irrespective of
> > > > > > > being ELF format or kdump-compressed format.
> > > > > > >
> > > > > > > Note: This doesn't support live debugging on ppc64,
since registers are not
> > > > > > > available to be read
> > > > > > >
> > > > > > > Implications on Architectures:
> > > > > > > ====================================
> > > > > > >
> > > > > > > No architecture other than PPC64 has been affected,
other than in case of
> > > > > > > 'frame' command
> > > > > > >
> > > > > > > As mentioned in patch #2, since frame will not be
prohibited, so it will print:
> > > > > > >
> > > > > > > crash> frame
> > > > > > > #0 <unavailable> in ?? ()
> > > > > > >
> > > > > > > Instead of before prohibited message:
> > > > > > >
> > > > > > > crash> frame
> > > > > > > crash: prohibited gdb command: frame
> > > > > > >
> > > > > > > Major change will be in 'gdb mode' on PPC64,
that it will print the frames, and
> > > > > > > local variables, instead of failing with errors showing
no frame, or showing
> > > > > > > that couldn't get PC, it will be able to give all
this information.
> > > > > > >
> > > > > > > Testing:
> > > > > > > ========
> > > > > > >
> > > > > > > Git tree with this patch series applied:
> > > > > > >
https://github.com/adi-g15-ibm/crash/tree/stack-unwind-v6
> > > > > > >
> > > > > > > To test various gdb passthroughs:
> > > > > > >
> > > > > > > (crash) set
> > > > > > > (crash) set gdb on
> > > > > > > gdb> thread
> > > > > > > gdb> bt
> > > > > > > gdb> info threads
> > > > > > > gdb> info threads
> > > > > > > gdb> info locals
> > > > > > > gdb> info variables irq_rover_lock
> > > > > > > gdb> info args
> > > > > > > gdb> thread 2
> > > > > > > gdb> set gdb off
> > > > > > > (crash) set
> > > > > > > (crash) set -c 6
> > > > > > > (crash) gdb thread
> > > > > > > (crash) bt
> > > > > > > (crash) gdb bt
> > > > > > > (crash) frame
> > > > > > > (crash) up
> > > > > > > (crash) down
> > > > > > > (crash) info locals
> > > > > > >
> > > > > > > Known Issues:
> > > > > > > =============
> > > > > > >
> > > > > > > 1. In gdb mode, 'bt' might fail to show
backtrace in few vmcores collected
> > > > > > > from older kernels. This is a known issue due to
register mismatch, and
> > > > > > > its fix has been merged upstream:
> > > > > > >
> > > > > > > This can also cause some 'invalid kernel
virtual address' errors during gdb
> > > > > > > unwinding the stack registers
> > > > > > >
> > > > > > > Commit:
https://github.com/torvalds/linux/commit/b684c09f09e7a6af3794d4233ef78581...
> > > > > > >
> > > > > > > Fixing GDB passthroughs on other architectures
> > > > > > > ==============================================
> > > > > > >
> > > > > > > Much of the work for making gdb passthroughs like
'gdb bt', 'gdb
> > > > > > > thread', 'gdb info locals' etc. has been
done by the patches introducing
> > > > > > > 'machdep->get_cpu_reg' and this series
fixing some issues in that.
> > > > > > >
> > > > > > > Other architectures should be able to fix these gdb
functionalities by
> > > > > > > simply implementing 'machdep->get_cpu_reg (cpu,
regno, ...)'.
> > > > > > >
> > > > > > > The reasoning behind that has been explained with a
diagram in commit
> > > > > > > description of patch #1
> > > > > > >
> > > > > > > I will assist with my findings/observations fixing it
on ppc64 whenever needed.
> > > > > > >
> > > > > > > Changelog:
> > > > > > > ==========
> > > > > > >
> > > > > > > V6:
> > > > > > > + changes in patch #5: fix bug introduced in v5 that
caused initial gdb thread
> > > > > > > to be thread 1
> > > > > > >
> > > > > > > V5:
> > > > > > > + changes in patch #1: made ppc64_get_cpu_reg static,
and remove unreachable
> > > > > > > code
> > > > > > > + changes in patch #3: fixed typo 'ppc64_renum'
instead of 'ppc64_regnum',
> > > > > > > remove unneeded if condition
> > > > > > > + changes in patch #5: implement refresh regcache on
per thread, instead of all
> > > > > > > threads at once
> > > > > > >
> > > > > > > V4:
> > > > > > > + fix segmentation fault in live debugging (change in
patch #1)
> > > > > > > + mention live debugging not supported in cover letter
and patch #1
> > > > > > > + fixed some checkpatch warnings (change in patch #5)
> > > > > > >
> > > > > > > V3:
> > > > > > > + default gdb thread will be the crashing thread,
instead of being
> > > > > > > thread '0'
> > > > > > > + synchronise crash cpu and gdb thread context
> > > > > > > + fix bug in gdb_interface, that replaced gdb's
output stream, losing
> > > > > > > output in some cases, such as info threads and extra
output in info
> > > > > > > variables
> > > > > > > + fix 'info threads'
> > > > > > >
> > > > > > > RFC V2:
> > > > > > > - removed patch implementing 'frame',
'up', 'down' in crash
> > > > > > > - updated the cover letter by removing the mention
of those commands other
> > > > > > > than the respective gdb passthrough
> > > > > > >
> > > > > > > Aditya Gupta (5):
> > > > > > > ppc64: correct gdb passthroughs by implementing
machdep->get_cpu_reg
> > > > > > > remove 'frame' from prohibited commands
list
> > > > > > > synchronise cpu context changes between crash/gdb
> > > > > > > fix gdb_interface: restore gdb's output streams
at end of
> > > > > > > gdb_interface
> > > > > > > fix 'info threads' command
> > > > > > >
> > > > > > > crash_target.c | 44 ++++++++++++++++
> > > > > > > defs.h | 130
+++++++++++++++++++++++++++++++++++++++++++++++-
> > > > > > > gdb-10.2.patch | 110
+++++++++++++++++++++++++++++++++++++++-
> > > > > > > gdb_interface.c | 2 +-
> > > > > > > kernel.c | 47 +++++++++++++++--
> > > > > > > ppc64.c | 95
+++++++++++++++++++++++++++++++++--
> > > > > > > task.c | 14 ++++++
> > > > > > > tools.c | 2 +-
> > > > > > > 8 files changed, 434 insertions(+), 10 deletions(-)
> > > > > > >
> > > > >
> > > >
> > >
> >
>