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@xxxxxxxx> > Debugged-by: Alistair Strachan <astrachan@xxxxxxxxxx> > Debugged-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx> > Reported-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > Suggested-by: Arnd Bergmann <arnd@xxxxxxxx> > Suggested-by: H. Peter Anvin <hpa@xxxxxxxxx> > Suggested-by: Tom Stellar <tstellar@xxxxxxxxxx> > Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> > --- > 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> Yeah, that makes sense, thanks for the backport. I'll queue it up after the next round of stable kernels comes out in a few days. greg k-h
