linux-kernel - Re: PROPOSAL: Extend inline asm syntax with size spec

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Date:   Wed, 31 Oct 2018 14:11:10 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Segher Boessenkool <segher@...nel.crashing.org>,
        Ingo Molnar <mingo@...nel.org>,
        Richard Biener <rguenther@...e.de>,
        Michael Matz <matz@...e.de>, gcc@....gnu.org,
        Nadav Amit <namit@...are.com>, Ingo Molnar <mingo@...hat.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Sam Ravnborg <sam@...nborg.org>,
        Alok Kataria <akataria@...are.com>,
        Christopher Li <sparse@...isli.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H. Peter Anvin" <hpa@...or.com>, Jan Beulich <JBeulich@...e.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Juergen Gross <jgross@...e.com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        Kees Cook <keescook@...omium.org>,
        linux-sparse@...r.kernel.org,
        Philippe Ombredanne <pombredanne@...b.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        virtualization@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Chris Zankel <chris@...kel.net>,
        Max Filippov <jcmvbkbc@...il.com>,
        linux-xtensa@...ux-xtensa.org,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: PROPOSAL: Extend inline asm syntax with size spec

On Wed, Oct 31, 2018 at 01:55:26PM +0100, Peter Zijlstra wrote:
> On Sat, Oct 13, 2018 at 09:33:35PM +0200, Borislav Petkov wrote:
> > Ok,
> > 
> > with Segher's help I've been playing with his patch ontop of bleeding
> > edge gcc 9 and here are my observations. Please double-check me for
> > booboos so that they can be addressed while there's time.
> > 
> > So here's what I see ontop of 4.19-rc7:
> > 
> > First marked the alternative asm() as inline and undeffed the "inline"
> > keyword. I need to do that because of the funky games we do with
> > "inline" redefinitions in include/linux/compiler_types.h.
> > 
> > And Segher hinted at either doing:
> > 
> > asm volatile inline(...
> > 
> > or
> > 
> > asm volatile __inline__(...
> > 
> > but both "inline" variants are defined as macros in that file.
> > 
> > Which means we either need to #undef inline before using it in asm() or
> > come up with something cleverer.
> 
> # git grep -e "\<__inline__\>" | wc -l
> 488
> # git grep -e "\<__inline\>" | wc -l
> 56
> # git grep -e "\<inline\>" | wc -l
> 69598
> 
> And we already have scripts/checkpatch.pl:
> 
>   # Check for __inline__ and __inline, prefer inline
> 
> Which suggests we do:
> 
> git grep -l "\<__inline\(\|__\)\>" | while read file
> do
> 	sed -i -e 's/\<__inline\(\|__\)\>/inline/g' $file
> done
> 
> and get it over with.
> 
> 
> Anyway, with the below patch, I get:
> 
>    text    data     bss     dec     hex filename
> 17385183        5064780 1953892 24403855        1745f8f defconfig-build/vmlinux
> 17385678        5064780 1953892 24404350        174617e defconfig-build/vmlinux

  17387603        5065468 1953892 24406963        1746bb3 defconfig-build/vmlinux

If I do an additional:

git grep -l "asm volatile" | while read file
do
	sed -i -e 's/asm volatile/asm_volatile/g' $file
done

on the tree...

No changes for:

-#define asm_volatile_goto(x...)        do { asm goto(x); asm (""); } while (0)
+#define asm_volatile_goto(x...)        do { asm __inline__ goto (x); asm (""); } while (0)

I suppose all our goto's are small now (my tree includes Nadav's patch
to static_cpu_has).