Re: [PATCH v3] ARM: kprobes: move __kretprobe_trampoline to out of line assembler

From: Chen Zhongjin <chenzhongjin@huawei.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: "Naveen N . Rao" <naveen.n.rao@linux.ibm.com>,
	Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>,
	"David S . Miller" <davem@davemloft.net>,
	Arnd Bergmann <arnd@arndb.de>,
	Nathan Chancellor <nathan@kernel.org>, Tom Rix <trix@redhat.com>,
	sparkhuang <huangshaobo6@huawei.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	<linux-arm-kernel@lists.infradead.org>,
	<linux-kernel@vger.kernel.org>, <linux-arch@vger.kernel.org>,
	<llvm@lists.linux.dev>,
	Naresh Kamboju <naresh.kamboju@linaro.org>,
	<regressions@lists.linux.dev>, <lkft-triage@lists.linaro.org>,
	"Linux Kernel Functional Testing" <lkft@linaro.org>,
	Logan Chien <loganchien@google.com>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	Russell King <rmk+kernel@armlinux.org.uk>
Subject: Re: [PATCH v3] ARM: kprobes: move __kretprobe_trampoline to out of line assembler
Date: Sat, 8 Oct 2022 11:10:36 +0800	[thread overview]
Message-ID: <6b4ccb6b-c6c2-e0cc-1670-1776877ecf46@huawei.com> (raw)
In-Reply-To: <CAKwvOd=0p31f-Yya6S-9xKEv6CtUWpOCRxHO=jG2uk-hZgZ1bQ@mail.gmail.com>

Hi,

Sorry for late reply because I just found this thread before the long 
vacation so I didn't have much time to deal with it.

On 2022/10/7 4:35, Nick Desaulniers wrote:
> On Fri, Sep 30, 2022 at 2:15 PM Nick Desaulniers
> <ndesaulniers@google.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?

Since 6.1 is closing now. Let's reorganize everything and queue it up 
for -next for 6.2

> 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?

This way looks good to me.

How about making a set for this,  to make everything more clear:

1. Move this out of line

2. Apply the feature, test with gcc & clang

3. Other cleaning, or merge with 2 if the cleaning is tiny.

I'll send another version for this, rebased to 6.1-rc1

Thanks for your time!

Best,

Chen

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