linux-kernel - Re: [PATCH -next 6/7] riscv: stacktrace: Fix unwinding on ftrace_regs

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Date:   Wed, 21 Sep 2022 09:43:54 +0800
From:   Guo Ren <guoren@...nel.org>
To:     Chen Zhongjin <chenzhongjin@...wei.com>
Cc:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-perf-users@...r.kernel.org, paul.walmsley@...ive.com,
        palmer@...belt.com, aou@...s.berkeley.edu, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org, mark.rutland@....com,
        alexander.shishkin@...ux.intel.com, namhyung@...nel.org,
        jolsa@...nel.org, nsaenzju@...hat.com, frederic@...nel.org,
        changbin.du@...el.com, vincent.chen@...ive.com, ardb@...nel.org,
        mhiramat@...nel.org, rostedt@...dmis.org, keescook@...omium.org,
        catalin.marinas@....com
Subject: Re: [PATCH -next 6/7] riscv: stacktrace: Fix unwinding on ftrace_regs_call

On Tue, Sep 20, 2022 at 11:15 PM Chen Zhongjin <chenzhongjin@...wei.com> wrote:
>
> When unwinding on ftrace_regs_call, the traced function will be skipped
> because ftrace_regs_caller doesn't save the fp and ra.
>
> Save the encoded fp so that we can get the pt_regs so that we can unwind
> from ftrace_regs_call to the traced function.
>
> Also the pt_regs->status should be set as kernel mode.
>
> Stacktrace before this patch:
>
>  Call Trace:
>   ...
>   [<ffffffff0161a0e0>] handler_pre+0x30/0x4a [kprobe_unwind]
>   [<ffffffff800bce92>] aggr_pre_handler+0x60/0x94
>   [<ffffffff80006df0>] kprobe_ftrace_handler+0x13e/0x188
>   [<ffffffff80008e7e>] ftrace_regs_call+0x8/0x10
>   [<ffffffff80002540>] do_one_initcall+0x4c/0x1f2
>   [<ffffffff8008a4e6>] do_init_module+0x56/0x210
>  ...
>
> Stacktrace after this patch:
>
>  Call Trace:
>   ...
>   [<ffffffff016150e0>] handler_pre+0x30/0x4a [kprobe_unwind]
>   [<ffffffff800bce96>] aggr_pre_handler+0x60/0x94
>   [<ffffffff80006df0>] kprobe_ftrace_handler+0x13e/0x188
>   [<ffffffff80008e82>] ftrace_regs_call+0x8/0x10
> + [<ffffffff01615000>] empty_call+0x0/0x1e [kprobe_unwind]
>   [<ffffffff80002540>] do_one_initcall+0x4c/0x1f2
>   [<ffffffff8008a4ea>] do_init_module+0x56/0x210
>   ...
>
> Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
> ---
>  arch/riscv/kernel/mcount-dyn.S | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
> index d171eca623b6..56a4014c392f 100644
> --- a/arch/riscv/kernel/mcount-dyn.S
> +++ b/arch/riscv/kernel/mcount-dyn.S
> @@ -10,6 +10,8 @@
>  #include <asm/asm-offsets.h>
>  #include <asm-generic/export.h>
>  #include <asm/ftrace.h>
> +#include <asm/frame.h>
> +#include <asm/csr.h>
>
>         .text
>
> @@ -97,6 +99,11 @@
>         REG_S x29, PT_T4(sp)
>         REG_S x30, PT_T5(sp)
>         REG_S x31, PT_T6(sp)
> +
> +#ifdef CONFIG_FRAME_POINTER
> +       li s0, SR_PP
> +       REG_S s0, PT_STATUS(sp)
Change another register.

> +#endif
>         .endm
>
>         .macro RESTORE_ALL
> @@ -172,6 +179,7 @@ ENDPROC(ftrace_caller)
>  #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>  ENTRY(ftrace_regs_caller)
>         SAVE_ALL
> +       ENCODE_FRAME_POINTER
Maybe the patch should merge with others, so separated make it hard to review.

>
>         addi    a0, ra, -FENTRY_RA_OFFSET
>         la      a1, function_trace_op
> --
> 2.17.1
>


--
Best Regards
 Guo Ren