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

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Date:   Mon, 10 Aug 2020 15:32:32 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Huckleberry <nhuck15@...il.com>
Cc:     Russell King <linux@...linux.org.uk>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chunyan Zhang <zhang.lyra@...il.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        LKML <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

On Thu, Aug 6, 2020 at 3:39 PM Nathan Huckleberry <nhuck15@...il.com> wrote:
>
> 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.

Yeah, I can add that.  It's a little orthogonal though to this patch
that renames labels. I'd consider more so a pre-existing bug.  Let me
add a patch to the series that gives it a new fixup handler, separate
from the label renaming, in a v2 of the series.

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



-- 
Thanks,
~Nick Desaulniers