Messages in this thread | | | Date | Tue, 26 May 2020 20:54:19 +0100 | From | Will Deacon <> | Subject | Re: [PATCH][V3] arm64: perf: Get the wrong PC value in REGS_ABI_32 mode |
| |
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?
Will
| |