On Tue, Mar 12, 2024 at 02:46:17PM +0800, Lianbo Jiang wrote:
> Hi, Aditya
>
> Sorry for the late reply.
>
> And thank you for improving the patchset. This looks better and test is ok
> for my side, so: Ack.
Hi Lianbo,
Thanks for the ack.
- Aditya Gupta
>
>
> Thanks
>
> Lianbo
>
> On 3/4/24 17:59, 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-v10
> >
> > 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) gdb up
> > (crash) gdb 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/b684c09f09e7a6af3794d4233ef785819e72db79
> >
> > 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:
> > ==========
> >
> > V10:
> > + introduce 'bt_info.need_free' to prevent memory leak in get_cpu_reg
> >
> > V9:
> > + minor change in patch #5: sync gdb context on a 'set' and 'set -p'
> > + add taoliu's patch for using current context, and fixes in ppc64_get_cpu_reg
> >
> > V8:
> > + use get_active_task instead of depending on CURRENT_CONTEXT in ppc64_get_cpu_reg
> > + rebase to upstream/master (5977936c0a91)
> >
> > V7:
> > + move changes in gdb-10.2.patch to the end (minor change in patch #3,4,5)
> > + fix a memory leak in ppc64_get_cpu_reg (minor change in patch #1)
> > + use ascii diagram in patch #1 description
> >
> > 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 | 57 ++++++++++++++++++++
> > defs.h | 131 ++++++++++++++++++++++++++++++++++++++++++++-
> > gdb-10.2.patch | 137 ++++++++++++++++++++++++++++++++++++++++++++++++
> > gdb_interface.c | 2 +-
> > kernel.c | 49 +++++++++++++++--
> > ppc64.c | 131 ++++++++++++++++++++++++++++++++++++++++++---
> > task.c | 32 ++++++++---
> > tools.c | 10 ++--
> > 8 files changed, 522 insertions(+), 27 deletions(-)
> >
>
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