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

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Message-Id: <20180607204927.219329-1-ndesaulniers@google.com>
Date:   Thu,  7 Jun 2018 13:49:24 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     akpm@...ux-foundation.org, hpa@...or.com, mingo@...hat.com,
        tglx@...utronix.de
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Subject: [PATCH v4 0/3] extern inline native_save_fl for paravirt

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