Messages in this thread | | | Date | Tue, 26 May 2020 11:26:11 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH][V3] arm64: perf: Get the wrong PC value in REGS_ABI_32 mode |
| |
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 reckon what we should do is have seperate functions for the two ABIs, to ensure we don't conflate them, e.g.
u64 perf_reg_value_abi32(struct pt_regs *regs, int idx) { if ((u32)idx > PERF_REG_ARM32_PC) return 0; if (idx == PERF_REG_ARM32_PC) return regs->pc; /* * Compat SP and LR already in-place */ return regs->regs[idx]; }
u64 perf_reg_value_abi64(struct pt_regs *regs, int idx) { if ((u32)idx > PERF_REG_ARM64_MAX) return 0; if ((u32)idx == PERF_REG_ARM64_SP) return regs->sp; if ((u32)idx == PERF_REG_ARM64_PC) return regs->pc; reutrn regs->regs[idx]; }
u64 perf_reg_value(struct pt_regs *regs, int idx) { if (compat_user_mode(regs)) return perf_reg_value_abi32(regs, idx); else return perf_reg_value_abi64(regs, idx); }
Thanks, Mark.
| |