linux-kernel - Re: [PATCH v3] ARM: kprobes: move __kretprobe

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Date:   Thu, 6 Oct 2022 13:35:03 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Chen Zhongjin <chenzhongjin@...wei.com>
Cc:     "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Tom Rix <trix@...hat.com>,
        sparkhuang <huangshaobo6@...wei.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, llvm@...ts.linux.dev,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        regressions@...ts.linux.dev, lkft-triage@...ts.linaro.org,
        Linux Kernel Functional Testing <lkft@...aro.org>,
        Logan Chien <loganchien@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Russell King <rmk+kernel@...linux.org.uk>
Subject: Re: [PATCH v3] ARM: kprobes: move __kretprobe_trampoline to out of
 line assembler

On Fri, Sep 30, 2022 at 2:15 PM Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
>
> commit 1069c1dd20a3 ("ARM: 9231/1: Recover kretprobes return address for
> EABI stack unwinder")
> tickled a bug in clang's integrated assembler where the .save and .pad
> directives must have corresponding .fnstart directives. The integrated
> assembler is unaware that the compiler will be generating the .fnstart
> directive.
>
>   arch/arm/probes/kprobes/core.c:409:30: error: .fnstart must precede
>   .save or .vsave directives
>   <inline asm>:3:2: note: instantiated into assembly here
>   .save   {sp, lr, pc}
>   ^
>   arch/arm/probes/kprobes/core.c:412:29: error: .fnstart must precede
>   .pad directive
>   <inline asm>:6:2: note: instantiated into assembly here
>   .pad    #52
>   ^
>

Chen, I noticed that your patch was discarded; it's not in linux-next today.
https://lore.kernel.org/linux-arm-kernel/YzHPGvhLkdQcDYzx@shell.armlinux.org.uk/
https://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=9231/1
How would you like to proceed here?

I think moving this out of line, incorporating Ard's feedback, then
putting the UNWIND directives on top might be the way to go. What do
you think?
-- 
Thanks,
~Nick Desaulniers