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Subject: Re: [PATCH 2/5] gcc-plugins/stackleak: Use asm instrumentation to
 avoid useless register saving
To:     Kees Cook <keescook@chromium.org>
Cc:     Emese Revfy <re.emese@gmail.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Andrew Morton <akpm@linux-foundation.org>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Jessica Yu <jeyu@kernel.org>,
        Sven Schnelle <svens@stackframe.org>,
        Iurii Zaikin <yzaikin@google.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
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        Mathias Krause <minipli@googlemail.com>,
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From:   Alexander Popov <alex.popov@linux.com>
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Message-ID: <ee1a5921-c151-33a9-bdac-c5d039a94bdc@linux.com>
Date:   Fri, 12 Jun 2020 02:45:00 +0300
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On 10.06.2020 23:03, Kees Cook wrote:
> On Wed, Jun 10, 2020 at 06:47:14PM +0300, Alexander Popov wrote:
>> On 09.06.2020 21:46, Kees Cook wrote:
>> The inline asm statement that is used for instrumentation is arch-specific.
>> Trying to add
>>   asm volatile("call stackleak_track_stack")
>> in gcc plugin on aarch64 makes gcc break spectacularly.
> 
> Ah! Thank you, that eluded my eyes. :)
> 
>> I pass the target arch name to the plugin and check it explicitly to avoid that.
>>
>> Moreover, I'm going to create a gcc enhancement request for supporting
>> no_caller_saved_registers attribute on aarch64.
> 
> For arm64 right now it looks like the plugin will just remain
> "inefficient" in these cleanup, as before, yes?

Yes, for arm64 the instrumentation didn't change in this patch series.
I checked the disasm and see the similar issue with useless register saving.

I'm going to add asm instrumentation for arm64 when (I hope) the
no_caller_saved_registers attribute becomes available for that platform.

Best regards,
Alexander