On Tue, 2021-07-06 at 12:43 +0200, Christophe Leroy wrote: > Le 04/07/2021 à 23:38, Radu Rendec a écrit : > > I'm trying to set up my (virtual) environment to test an old bug in the > > PPC32 ptrace() code. I came across a completely different problem, > > which seems to make gdb pretty much unusable on PPC32. I'm not sure if > > this is a real kernel bug or maybe something wrong with my > > configuration. > > > > I'm running kernel 5.13 in a qemu VM with one e500mc CPU. I am running > > native gdb (inside the VM) and setting a breakpoint in main() in a test > > "hello world" program. Upon running the test program, I am hitting the > > BUG_ON in do_notify_resume() on line 292. The kernel bug log snippet is > > included below at the end of the email. > > > > FWIW, gdb says: > > Program terminated with signal SIGTRAP, Trace/breakpoint trap. > > The program no longer exists. > > > > I also added a pr_info() to do_notify_resume() just to see how much > > different 'regs' and 'current->thread.regs' are. Surprisingly, they are > > just 0x30 apart: regs=c7955f10 cur=c7955f40. Also, 'current' seems to > > be OK (pid and comm are consistent with the test program). > > The TRAP = 0x7d8 is obviously wrong. > > Need to know which 'TRAP' it is exactly. > Could you try to dump what we have at the correct regs ? > Something like 'show_regs(current->thread.regs)' should do it.
Sure, please see the output below. It looks to me like the "correct" regs are just garbage. Either they are overwritten or current->thread.regs is wrong. But in any case, r1 = 0 doesn't look good. regs=c7a0ff10 cur=c7a0ff40 pid=139 comm=test CPU: 0 PID: 139 Comm: test Not tainted 5.13.0-dirty #4 NIP: 10000338 LR: 00030000 CTR: 00000003 REGS: c7a0ff40 TRAP: 670000 Not tainted (5.13.0-dirty) MSR: 1002d202 <CE,EE,PR,ME,DE> CR: 10000004 XER: 80670100 GPR00: b7fc36d8 00000000 00000000 b7fe17b4 00000000 b7ffd588 b7ffe8b8 b7ffee10 GPR08: b7fff214 b7ffdf40 b7fff208 bffff858 bffff970 b7fff130 00000001 bffff960 GPR16: b7fff2b0 b7ffd5f0 b7ffe8a8 bffff850 b7fc3714 1002d002 b7fff208 00000003 GPR24: b7fc3714 00000000 22000284 bffff960 000007d8 10000338 08000000 bffff850 NIP [10000338] 0x10000338 LR [00030000] 0x30000 Call Trace: [c7a0fe40] [c0008eac] show_regs+0x4c/0x1b0 (unreliable) [c7a0fe80] [c000969c] do_notify_resume+0x31c/0x320 [c7a0fee0] [c0010b94] interrupt_exit_user_prepare+0x94/0xc0 [c7a0ff00] [c00151e8] interrupt_return+0x14/0x13c --- interrupt: 7d8 at 0xb7fc3714 NIP: b7fc3714 LR: b7fc3714 CTR: 00000003 REGS: c7a0ff10 TRAP: 07d8 Not tainted (5.13.0-dirty) MSR: 1002d002 <CE,EE,PR,ME> CR: 22000284 XER: 00000000 GPR00: b7fc3584 bffff850 00000000 00000000 00000000 00000000 000000a0 6474e552 GPR08: b7fbe0d4 00000001 b7fff230 bffff850 b7fc36d8 00000000 00000000 b7fe17b4 GPR16: 00000000 b7ffd588 b7ffe8b8 b7ffee10 b7fff214 b7ffdf40 b7fff208 bffff858 GPR24: bffff970 b7fff130 00000001 bffff960 b7fff2b0 b7ffd5f0 b7ffe8a8 bffff850 NIP [b7fc3714] 0xb7fc3714 LR [b7fc3714] 0xb7fc3714 --- interrupt: 7d8 ------------[ cut here ]------------ kernel BUG at arch/powerpc/kernel/signal.c:298! Oops: Exception in kernel mode, sig: 5 [#1] BE PAGE_SIZE=4K SMP NR_CPUS=24 QEMU e500 Modules linked in: CPU: 0 PID: 139 Comm: test Not tainted 5.13.0-dirty #4 NIP: c000969c LR: c000969c CTR: c065f540 REGS: c7a0fdc0 TRAP: 0700 Not tainted (5.13.0-dirty) MSR: 00028002 <CE,EE> CR: 28000282 XER: 20000000 GPR00: c000969c c7a0fe80 c70ef500 c70efbd8 c70ef500 00000010 c7a0fc38 00000002 GPR08: 00000001 00000000 00000000 00000000 28000282 00000000 00000000 b7fe17b4 GPR16: 00000000 b7ffd588 b7ffe8b8 b7ffee10 b7fff214 b7ffdf40 b7fff208 bffff858 GPR24: bffff970 b7fff130 00000001 bffff960 c7a0ff10 00000800 c70ef500 00000102 NIP [c000969c] do_notify_resume+0x31c/0x320 LR [c000969c] do_notify_resume+0x31c/0x320 Call Trace: [c7a0fe80] [c000969c] do_notify_resume+0x31c/0x320 (unreliable) [c7a0fee0] [c0010b94] interrupt_exit_user_prepare+0x94/0xc0 [c7a0ff00] [c00151e8] interrupt_return+0x14/0x13c --- interrupt: 7d8 at 0xb7fc3714 NIP: b7fc3714 LR: b7fc3714 CTR: 00000003 REGS: c7a0ff10 TRAP: 07d8 Not tainted (5.13.0-dirty) MSR: 1002d002 <CE,EE,PR,ME> CR: 22000284 XER: 00000000 GPR00: b7fc3584 bffff850 00000000 00000000 00000000 00000000 000000a0 6474e552 GPR08: b7fbe0d4 00000001 b7fff230 bffff850 b7fc36d8 00000000 00000000 b7fe17b4 GPR16: 00000000 b7ffd588 b7ffe8b8 b7ffee10 b7fff214 b7ffdf40 b7fff208 bffff858 GPR24: bffff970 b7fff130 00000001 bffff960 b7fff2b0 b7ffd5f0 b7ffe8a8 bffff850 NIP [b7fc3714] 0xb7fc3714 LR [b7fc3714] 0xb7fc3714 --- interrupt: 7d8 Instruction dump: 93a10054 90010064 93c10058 48b95369 80c20398 3c60c0dc 7f84e378 38e204b0 3863ce30 4809d819 80620704 4bfff7c9 <0fe00000> 3d20c0ff 8129c014 2c090000 ---[ end trace 1cbf27cd19ae39a0 ]--- > > If I'm not missing something, the 'regs' pointer that is eventually > > passed to do_notify_resume() is calculated in interrupt_return() by > > adding STACK_FRAME_OVERHEAD (defined to 112) to the value of r1. That > > means all registers are saved on the stack before entering the > > interrupt handler and, upon returning, a pointer to the register > > structure is calculated from the stack pointer. Either the offset > > itself is wrong, or the stack pointer is off by 0x30. > > > > This is as far as I have gone. Hopefully this rings a bell to someone > > who is familiar with that part of the code and has a better > > understanding of PPC32 interrupt handling in general. > > > > Last but not least, my configuration is fairly standard. I'm using the > > powerpc-e500mc--glibc--bleeding-edge-2020.08-1 toolchain from Bootlin > > to compile everything (kernel and user-space). The qemu version is > > 5.2.0 (Fedora 34) and the user-space is a small Busybox based rootfs > > that I built using Buildroot 2021.05. The gdb version is 9.2.
