Sorry, please ignore this patch. It's incomplete. On 09/02/24 11:34, 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-v8 > > 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/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: > ========== > > V8: > + use get_active_task instead of depending on CURRENT_CONTEXT in ppc64_get_cpu_reg > > 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 | 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(-) >