linux-kernel - Re: [PATCH 3/4] ARM: backtrace-clang: give labels more descriptive names

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Message-ID: <CAN=-RxstJBjJUcOf9iuAxEcxYUhJTdF9JhPVWwQuefnE+3s52w@mail.gmail.com>
Date:   Thu, 6 Aug 2020 17:39:33 -0500
From:   Nathan Huckleberry <nhuck15@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        clang-built-linux@...glegroups.com,
        Dmitry Safonov <0x7f454c46@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mediatek@...ts.infradead.org,
        Lvqiang Huang <lvqiang.huang@...soc.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Miles Chen <miles.chen@...iatek.com>,
        Nathan Huckleberry <nhuck@...gle.com>
Subject: Re: [PATCH 3/4] ARM: backtrace-clang: give labels more descriptive names

The style cleanup looks great. I just have one extra thing that
can probably be thrown into this patch.

On Thu, Jul 30, 2020 at 3:51 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> Removes the 1004 label; it was neither a control flow target, nor an
> instruction we expect to produce a fault.
>
> Gives the labels slightly more readable names. The `b` suffixes are
> handy to disambiguate between labels of the same identifier when there's
> more than one. Since these labels are unique, let's just give them
> names.
>
> Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
> ---
>  arch/arm/lib/backtrace-clang.S | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/arch/arm/lib/backtrace-clang.S b/arch/arm/lib/backtrace-clang.S
> index 40eb2215eaf4..7dad2a6843a5 100644
> --- a/arch/arm/lib/backtrace-clang.S
> +++ b/arch/arm/lib/backtrace-clang.S
> @@ -121,8 +121,8 @@ for_each_frame:     tst     frame, mask             @ Check for address exceptions
>   * start. This value gets updated to be the function start later if it is
>   * possible.
>   */
> -1001:          ldr     sv_pc, [frame, #4]      @ get saved 'pc'
> -1002:          ldr     sv_fp, [frame, #0]      @ get saved fp
> +load_pc:       ldr     sv_pc, [frame, #4]      @ get saved 'pc'
> +load_fp:       ldr     sv_fp, [frame, #0]      @ get saved fp
>
>                 teq     sv_fp, mask             @ make sure next frame exists
>                 beq     no_frame
> @@ -142,7 +142,7 @@ for_each_frame:     tst     frame, mask             @ Check for address exceptions
>   * registers for the current function, but the stacktrace is still printed
>   * properly.
>   */
> -1003:          ldr     sv_lr, [sv_fp, #4]      @ get saved lr from next frame
> +load_lr:       ldr     sv_lr, [sv_fp, #4]      @ get saved lr from next frame
>
>                 tst     sv_lr, #0               @ If there's no previous lr,
>                 beq     finished_setup          @ we're done.
> @@ -166,8 +166,7 @@ finished_setup:
>  /*
>   * Print the function (sv_pc) and where it was called from (sv_lr).
>   */
> -1004:          mov     r0, sv_pc
> -
> +               mov     r0, sv_pc
>                 mov     r1, sv_lr
>                 mov     r2, frame
>                 bic     r1, r1, mask            @ mask PC/LR for the mode
> @@ -182,7 +181,7 @@ finished_setup:
>   * pointer the comparison will fail and no registers will print. Unwinding will
>   * continue as if there had been no registers stored in this frame.
>   */
> -1005:          ldr     r1, [sv_pc, #0]         @ if stmfd sp!, {..., fp, lr}
> +load_stmfd:    ldr     r1, [sv_pc, #0]         @ if stmfd sp!, {..., fp, lr}
>                 ldr     r3, .Lopcode            @ instruction exists,
>                 teq     r3, r1, lsr #11
>                 ldr     r0, [frame]             @ locals are stored in
> @@ -201,7 +200,7 @@ finished_setup:
>                 mov     frame, sv_fp            @ above the current frame
>                 bhi     for_each_frame
>
> -1006:          adr     r0, .Lbad
> +bad_frame:     adr     r0, .Lbad
>                 mov     r1, loglvl
>                 mov     r2, frame
>                 bl      printk
> @@ -216,11 +215,10 @@ bad_lr:           mov     sv_fp, #0
>  ENDPROC(c_backtrace)
>                 .pushsection __ex_table,"a"
>                 .align  3
> -               .long   1001b, 1006b
> -               .long   1002b, 1006b
> -               .long   1003b, 1006b
> -               .long   1004b, 1006b
> -               .long   1005b, 1006b
> +               .long   load_pc, bad_frame
> +               .long   load_fp, bad_frame
> +               .long   load_lr, bad_frame
> +               .long   load_stmfd, bad_frame

Load_stmfd should get its own fixup
handler since it should emit errors about a bad
pc, not a bad frame pointer.

>                 .long   prev_call, bad_lr
>                 .popsection
>
> --
> 2.28.0.163.g6104cc2f0b6-goog
>