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Message-ID: <20200416071023.GB29742@willie-the-truck>
Date: Thu, 16 Apr 2020 08:10:24 +0100
From: Will Deacon <will@...nel.org>
To: Jiping Ma <jiping.ma2@...driver.com>
Cc: will.deacon@....com, mark.rutland@....com, catalin.marinas@....com,
alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
namhyung@...nel.org, peterz@...radead.org, mingo@...hat.com,
acme@...nel.org, linux-kernel@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] Perf: support to unwind userspace application stacks
generated with thumb.
On Thu, Apr 16, 2020 at 01:38:29PM +0800, Jiping Ma wrote:
> Only push sp and lr in the stack for thumb mode. it will go
> through the stack find sp and lr.
>
> Change this to the more detailed description of the patch
>
> Signed-off-by: Jiping Ma <jiping.ma2@...driver.com>
> ---
> arch/arm64/kernel/perf_callchain.c | 36 +++++++++++++++++++++++++++---
> 1 file changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
> index bcafd7dcfe8b..97dde271c121 100644
> --- a/arch/arm64/kernel/perf_callchain.c
> +++ b/arch/arm64/kernel/perf_callchain.c
> @@ -104,6 +104,30 @@ compat_user_backtrace(struct compat_frame_tail __user *tail,
>
> return (struct compat_frame_tail __user *)compat_ptr(buftail.fp) - 1;
> }
> +
> +void
> +user_backtrace_thumb(struct perf_callchain_entry_ctx *entry,
> + struct pt_regs *regs)
> +{
> + u32 sp;
> + u32 *sp_t;
> + /*
> + * Only push sp, lr to stack.
> + */
> + for (sp = regs->compat_sp; (sp < current->mm->start_stack) &&
> + (entry->nr < entry->max_stack); sp += 4) {
> + sp_t = (u32 *)(unsigned long)sp;
> + if ((*sp_t > regs->compat_sp) &&
> + (*sp_t < current->mm->start_stack)) {
> + if (*(sp_t + 1) < current->mm->end_code &&
> + *(sp_t + 1) > current->mm->start_code) {
> + perf_callchain_store(entry, *(sp_t + 1)-1);
> + sp += 4;
> + }
> + }
> + }
> +}
This looks like a pile of fragile heuristics to me. Why don't you just use
libunwind in userspace, the same way you'd have to if you compiled without
framepointers?
Will
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