lkml.org 
[lkml]   [2019]   [Nov]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] arm64: perf: Report arm pc registers for compat perf
On Tue, Nov 12, 2019 at 10:01:41AM +0900, Seung-Woo Kim wrote:
> If perf is built as arm 32-bit, it only reads 15 registers as arm
> 32-bit register map and this breaks dwarf call-chain in compat
> perf because pc register information is not filled.
> Report arm pc registers for 32-bit compat perf.
>
> Without this, arm 32-bit perf dwarf call-graph shows below
> verbose message:
> unwind: reg 15, val 0
> unwind: reg 13, val ffbc6360
> unwind: no map for 0
>
> Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
> ---
> arch/arm64/kernel/perf_regs.c | 2 ++
> 1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/arch/arm64/kernel/perf_regs.c b/arch/arm64/kernel/perf_regs.c
> index 0bbac61..d4172e7 100644
> --- a/arch/arm64/kernel/perf_regs.c
> +++ b/arch/arm64/kernel/perf_regs.c
> @@ -24,6 +24,8 @@ u64 perf_reg_value(struct pt_regs *regs, int idx)
> return regs->compat_sp;
> if ((u32)idx == PERF_REG_ARM64_LR)
> return regs->compat_lr;
> + if ((u32)idx == 15) /* PERF_REG_ARM_PC */
> + return regs->pc;
> }

This doesn't look quite right to me, since perf_regs_value() is
consuming the arm64 index for all other registers (e.g. the LR, in the
patch context).

i.e. this is designed for a native arm64 caller, and the fixup allows it
to view a compat task's registers as-if it were native.

How does this work for a native arm64 perf invocation with a compat
task? I assume it consumers regs->pc, and works as expected?

I suspect we need separate native and compat forms of this function, but
then it's not entirely clear how this should work -- how does this work
for a compat perf analysing a native arm64 binary?

Thanks,
Mark.

\
 
 \ /
  Last update: 2019-11-12 10:41    [W:0.078 / U:1.468 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site