lkml.org 
[lkml]   [2018]   [Jul]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [4.4 STABLE BACKPORT] x86: paravirt: make native_save_fl extern inline
On Fri, Jul 20, 2018 at 03:36:41PM -0700, Nick Desaulniers wrote:
> 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.
>
> Acked-by: Juergen Gross <jgross@suse.com>
> Debugged-by: Alistair Strachan <astrachan@google.com>
> Debugged-by: Matthias Kaehlcke <mka@chromium.org>
> Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Suggested-by: H. Peter Anvin <hpa@zytor.com>
> Suggested-by: Tom Stellar <tstellar@redhat.com>
> Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
> ---
> Backport for 4.4. 4.4 is missing commit 784d5699eddc "x86: move exports to
> actual definitions" which doesn't apply cleanly, and not really worth
> backporting IMO. It's simpler to change this patch from upstream:
> + #include <asm-generic/export.h>
> rather than
> + #include <asm/export.h>

Now applied, thanks.

greg k-h

\
 
 \ /
  Last update: 2018-07-23 09:58    [W:0.075 / U:0.860 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site