[PATCH v2 0/2] extern inline native_save_fl for paravirt

From: Nick Desaulniers
Date: Tue Jun 05 2018 - 13:17:23 EST


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 v2:
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.

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/irqflags.h | 2 +-
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/irqflags.S | 26 ++++++++++++++++++++++++++
include/linux/compiler-gcc.h | 19 +++++++++++++------
4 files changed, 41 insertions(+), 7 deletions(-)
create mode 100644 arch/x86/kernel/irqflags.S

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2.17.1.1185.g55be947832-goog