linux-kernel - Re: [PATCH v5 0/3] extern inline native_save

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Message-ID: <CA+icZUWW8yxxdQHC6gkqXnTkW70tLbL1Rmpa5dfVyihWSb9hLQ@mail.gmail.com>
Date:   Thu, 14 Jun 2018 15:20:53 +0200
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Nick Desaulniers <ndesaulniers@...gle.com>
Cc:     akpm@...ux-foundation.org, hpa@...or.com, mingo@...hat.com,
        tglx@...utronix.de, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        virtualization@...ts.linux-foundation.org, astrachan@...gle.com,
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        keescook@...gle.com, yamada.masahiro@...ionext.com,
        michal.lkml@...kovi.net, linux-kbuild@...r.kernel.org,
        geert@...ux-m68k.org, will.deacon@....com, mawilcox@...rosoft.com,
        Arnd Bergmann <arnd@...db.de>, rientjes@...gle.com,
        acme@...hat.com, pombredanne@...b.com, aryabinin@...tuozzo.com,
        kstewart@...uxfoundation.org, boris.ostrovsky@...cle.com,
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        jpoimboe@...hat.com, mka@...omium.org, thomas.lendacky@....com,
        tweek@...gle.com, mjg59@...gle.com, joe@...ches.com,
        andrea.parri@...rulasolutions.com
Subject: Re: [PATCH v5 0/3] extern inline native_save_fl for paravirt

On Wed, Jun 13, 2018 at 11:05 PM, Nick Desaulniers
<ndesaulniers@...gle.com> wrote:
> paravirt depends on a custom calling convention (callee saved), but
> expects this from a static inline function that it then forces to be
> outlined. This is problematic because different compilers or flags can
> then add a stack guard that violates the calling conventions.
>
> Uses extern inline with the out-of-line definition in assembly to
> prevent compilers from adding stack guards to the outlined version.
>
> Other parts of the codebase overwrite KBUILD_CFLAGS, which is *extremely
> problematic* for extern inline, as the sematics are completely the
> opposite depending on what C standard is used.
> http://blahg.josefsipek.net/?p=529
>
> Changes since v4:
>   Take Arnd's and hpa's suggestions properly feature detect gnu_inline
>   attribute to support gcc 4.1.
>
> Changes since v3:
>   Take Joe's suggestion to hoist __inline__ and __inline out of
>   conditional block.
>
> Changes since v2:
>   Take hpa's _ASM_ARG patch into the set in order to simplify cross
>   32b/64b x86 assembly and rebase my final patch to use it.  Apply
>   Sedat's typo fix to commit message and sign off on it. Take Joe's
>   suggestion to simplify __inline__ and __inline. Add Arnd to list of
>   folks who made helpful suggestions.
>
> Changes since v1:
>   Prefer gnu_inline function attribute instead of explicitly setting C
>   standard compiler flag in problematic Makefiles. We should instead
>   carefully evaluate if those Makefiles should be overwriting
>   KBUILD_CFLAGS at all. Dropped the previous first two patches and added
>   a new first patch.
>
> H. Peter Anvin (1):
>   x86/asm: add _ASM_ARG* constants for argument registers to <asm/asm.h>
>
> Nick Desaulniers (2):
>   compiler-gcc.h: add gnu_inline to all inline declarations
>   x86: paravirt: make native_save_fl extern inline
>
>  arch/x86/include/asm/asm.h      | 59 +++++++++++++++++++++++++++++++++
>  arch/x86/include/asm/irqflags.h |  2 +-
>  arch/x86/kernel/Makefile        |  1 +
>  arch/x86/kernel/irqflags.S      | 26 +++++++++++++++
>  include/linux/compiler-gcc.h    | 29 ++++++++++++----
>  5 files changed, 109 insertions(+), 8 deletions(-)
>  create mode 100644 arch/x86/kernel/irqflags.S
>
> --
> 2.18.0.rc1.244.gcf134e6275-goog
>

Hi Nick,

thanks for v5 of your patchset.

I was able to boot into bare metal.

root@...za:~# cat /proc/version
Linux version 4.14.49-1-iniza-llvmlinux (sedat.dilek@...il.com@...za)
(clang version 7.0.0- (trunk)) #1 SMP 2018-06-14

root@...za:~# dpkg -l | grep clang-7
ii  clang-7
1:7~svn334344-1~exp1+0~20180609091248.1814~1.gbp8ccab3 amd64        C,
C++ and Objective-C compiler

Feel free to add my Tested-By.

Regards,
- Sedat -