linux-kernel - Re: [PATCH v4 0/3] extern inline native_save

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Date:   Fri, 8 Jun 2018 14:22:43 +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,
        manojgupta@...gle.com, ghackmann@...gle.com, tstellar@...hat.com,
        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,
        jan.kiszka@...mens.com, rostedt@...dmis.org,
        kirill.shutemov@...ux.intel.com, ard.biesheuvel@...aro.org,
        akataria@...are.com, brijesh.singh@....com,
        caoj.fnst@...fujitsu.com, gregkh@...uxfoundation.org,
        jarkko.sakkinen@...ux.intel.com, jgross@...e.com,
        jpoimboe@...hat.com, mka@...omium.org, thomas.lendacky@....com,
        tweek@...gle.com, mjg59@...gle.com, joe@...ches.com
Subject: Re: [PATCH v4 0/3] extern inline native_save_fl for paravirt

On Thu, Jun 7, 2018 at 10:49 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 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    | 17 ++++++----
>  5 files changed, 97 insertions(+), 8 deletions(-)
>  create mode 100644 arch/x86/kernel/irqflags.S
>
> --
> 2.17.1.1185.g55be947832-goog
>

Tested v4 against Linux v4.14.48 and clang 7-svn333836 and booted on
bare metal/hardware.

- Sedat -

View attachment "dmesg_4.14.48-1-iniza-llvmlinux.txt" of type "text/plain" (67963 bytes)

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