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Nick Desaulniers d0a8d9378d x86/paravirt: Make native_save_fl() extern inline 
native_save_fl() is marked static inline, but by using it as
a function pointer in arch/x86/kernel/paravirt.c, it MUST be outlined.

paravirt's use of native_save_fl() also requires that no GPRs other than
%rax are clobbered.

Compilers have different heuristics which they use to emit stack guard
code, the emittance of which can break paravirt's callee saved assumption
by clobbering %rcx.

Marking a function definition extern inline means that if this version
cannot be inlined, then the out-of-line version will be preferred. By
having the out-of-line version be implemented in assembly, it cannot be
instrumented with a stack protector, which might violate custom calling
conventions that code like paravirt rely on.

The semantics of extern inline has changed since gnu89. This means that
folks using GCC versions >= 5.1 may see symbol redefinition errors at
link time for subdirs that override KBUILD_CFLAGS (making the C standard
used implicit) regardless of this patch. This has been cleaned up
earlier in the patch set, but is left as a note in the commit message
for future travelers.

Reports:
 https://lkml.org/lkml/2018/5/7/534
 https://github.com/ClangBuiltLinux/linux/issues/16

Discussion:
 https://bugs.llvm.org/show_bug.cgi?id=37512
 https://lkml.org/lkml/2018/5/24/1371

Thanks to the many folks that participated in the discussion.

Debugged-by: Alistair Strachan <astrachan@google.com>
Debugged-by: Matthias Kaehlcke <mka@chromium.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Suggested-by: H. Peter Anvin <hpa@zytor.com>
Suggested-by: Tom Stellar <tstellar@redhat.com>
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Acked-by: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@redhat.com
Cc: akataria@vmware.com
Cc: akpm@linux-foundation.org
Cc: andrea.parri@amarulasolutions.com
Cc: ard.biesheuvel@linaro.org
Cc: aryabinin@virtuozzo.com
Cc: astrachan@google.com
Cc: boris.ostrovsky@oracle.com
Cc: brijesh.singh@amd.com
Cc: caoj.fnst@cn.fujitsu.com
Cc: geert@linux-m68k.org
Cc: ghackmann@google.com
Cc: gregkh@linuxfoundation.org
Cc: jan.kiszka@siemens.com
Cc: jarkko.sakkinen@linux.intel.com
Cc: joe@perches.com
Cc: jpoimboe@redhat.com
Cc: keescook@google.com
Cc: kirill.shutemov@linux.intel.com
Cc: kstewart@linuxfoundation.org
Cc: linux-efi@vger.kernel.org
Cc: linux-kbuild@vger.kernel.org
Cc: manojgupta@google.com
Cc: mawilcox@microsoft.com
Cc: michal.lkml@markovi.net
Cc: mjg59@google.com
Cc: mka@chromium.org
Cc: pombredanne@nexb.com
Cc: rientjes@google.com
Cc: rostedt@goodmis.org
Cc: thomas.lendacky@amd.com
Cc: tweek@google.com
Cc: virtualization@lists.linux-foundation.org
Cc: will.deacon@arm.com
Cc: yamada.masahiro@socionext.com
Link: http://lkml.kernel.org/r/20180621162324.36656-4-ndesaulniers@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2018-07-03 10:56:27 +02:00
..
alpha alpha: Remove custom dec_and_lock() implementation 2018-06-12 23:33:24 +02:00
arc mm: introduce ARCH_HAS_PTE_SPECIAL 2018-06-07 17:34:35 -07:00
arm ARM: SoC fixes for 4.18-rc 2018-06-30 14:08:06 -07:00
arm64 ARM: SoC fixes for 4.18-rc 2018-06-30 14:08:06 -07:00
c6x Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-06-04 20:27:54 -07:00
h8300 Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-06-04 20:27:54 -07:00
hexagon hexagon: drop the unused variable zero_page_mask 2018-06-15 07:55:25 +09:00
ia64 - Error path bug fix for overflow tests (Dan) 2018-06-12 18:28:00 -07:00
m68k Merge branch 'for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gerg/m68knommu 2018-06-05 10:51:30 -07:00
microblaze Microblaze patches for 4.18-rc3 2018-06-27 09:49:30 -07:00
mips MIPS: Add ksig argument to rseq_{signal_deliver,handle_notify_resume} 2018-06-24 10:33:03 -07:00
nds32 Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-06-04 20:27:54 -07:00
nios2 Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2018-06-04 20:27:54 -07:00
openrisc Kbuild updates for v4.18 2018-06-06 11:00:15 -07:00
parisc parisc: Build kernel without -ffunction-sections 2018-06-29 17:27:20 +02:00
powerpc Kbuild fixes for v4.18 2018-06-30 13:05:30 -07:00
riscv RISC-V Updates for the 4.18 Merge Window 2018-06-16 06:42:43 +09:00
s390 Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/s390/linux 2018-06-19 07:44:51 +09:00
sh arch/*: Kconfig: fix documentation for NMI watchdog 2018-06-15 12:48:59 -03:00
sparc arch/*: Kconfig: fix documentation for NMI watchdog 2018-06-15 12:48:59 -03:00
um Solve a series of broken links for files under Documentation: 2018-06-17 05:25:18 +09:00
unicore32 docs: Fix some broken references 2018-06-15 18:10:01 -03:00
x86 x86/paravirt: Make native_save_fl() extern inline 2018-07-03 10:56:27 +02:00
xtensa docs: Fix some broken references 2018-06-15 18:10:01 -03:00
.gitignore
Kconfig docs: Fix some broken references 2018-06-15 18:10:01 -03:00