linux-kernel - Re: [clang] stack protector and f1f029c7bf

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Date:   Fri, 25 May 2018 14:06:28 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     Alistair Strachan <astrachan@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Matthias Kaehlcke <mka@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>, sedat.dilek@...il.com,
        tstellar@...hat.com, LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...gle.com>
Subject: Re: [clang] stack protector and f1f029c7bf

On 05/25/18 13:36, Nick Desaulniers wrote:
> On Fri, May 25, 2018 at 10:56 AM <hpa@...or.com> wrote:
>> You need the extern inline in the .h file and the out-of-line .S file
> both.
> 
> But the out-of-line .S file looks like:
> 
> ...
>     10 ENTRY(native_save_fl)
> 
>     11   pushf
> 
>     12   pop %_ASM_AX
> 
>     13   ret
> 
>     14 ENDPROC(native_save_fl)
> 
>     15 EXPORT_SYMBOL(native_save_fl)
> ...
> 
> I don't see how you can specify to the linker from assembly source that
> this function should be treated as `extern inline`?
> 

"extern inline" is a C directive. In the header file you should provide
the inlinable implementation (which is already there.) It means that "if
you don't want to inline this there is an external implementation
available."


> I assume you don't literally mean the C keywords `extern inline` but
> whatever the equivalent incantation is needed in terms of assembler
> directives (which I also don't know).
> 
> I'm beginning to think that what you'd like to see cannot be expressed (at
> least via `extern inline`).
>