Messages in this thread | | | Subject | Re: [PATCH][V3] arm64: perf: Get the wrong PC value in REGS_ABI_32 mode | From | Jiping Ma <> | Date | Wed, 27 May 2020 09:30:01 +0800 |
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On 05/27/2020 03:54 AM, Will Deacon wrote: > On Tue, May 26, 2020 at 11:26:11AM +0100, Mark Rutland wrote: >> On Mon, May 11, 2020 at 10:52:07AM +0800, Jiping Ma wrote: >>> Modified the patch subject and the change description. >>> >>> PC value is get from regs[15] in REGS_ABI_32 mode, but correct PC >>> is regs->pc(regs[PERF_REG_ARM64_PC]) in arm64 kernel, which caused >>> that perf can not parser the backtrace of app with dwarf mode in the >>> 32bit system and 64bit kernel. >>> >>> Signed-off-by: Jiping Ma <jiping.ma2@windriver.com> >> Thanks for this. >> >> >>> --- >>> arch/arm64/kernel/perf_regs.c | 4 ++++ >>> 1 file changed, 4 insertions(+) >>> >>> diff --git a/arch/arm64/kernel/perf_regs.c b/arch/arm64/kernel/perf_regs.c >>> index 0bbac61..0ef2880 100644 >>> --- a/arch/arm64/kernel/perf_regs.c >>> +++ b/arch/arm64/kernel/perf_regs.c >>> @@ -32,6 +32,10 @@ u64 perf_reg_value(struct pt_regs *regs, int idx) >>> if ((u32)idx == PERF_REG_ARM64_PC) >>> return regs->pc; >>> >>> + if (perf_reg_abi(current) == PERF_SAMPLE_REGS_ABI_32 >>> + && idx == 15) >>> + return regs->pc; >> I think there are some more issues here, and we may need a more >> substantial rework. For a compat thread, we always expose >> PERF_SAMPLE_REGS_ABI_32 via per_reg_abi(), but for some reason >> perf_reg_value() also munges the compat SP/LR into their ARM64 >> equivalents, which don't exist in the 32-bit sample ABI. We also don't >> zero the regs that don't exist in 32-bit (including the aliasing PC). > I think this was for the case where you have a 64-bit perf profiling a > 32-bit task, and it was passing the registers off to libunwind. Won't that > break if we follow your suggestion? Yes, it is for 64-bit perf profiling a 32-bit task, not for a compat thread.
> > Will >
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