On Thu, Jun 7, 2018 at 11:32 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> 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. > > 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> > --- > arch/x86/include/asm/irqflags.h | 2 +- > arch/x86/kernel/Makefile | 1 + > arch/x86/kernel/irqflags.S | 26 ++++++++++++++++++++++++++ > 3 files changed, 28 insertions(+), 1 deletion(-) > create mode 100644 arch/x86/kernel/irqflags.S > > diff --git a/arch/x86/include/asm/irqflags.h b/arch/x86/include/asm/irqflags.h > index 89f08955fff7..c4fc17220df9 100644 > --- a/arch/x86/include/asm/irqflags.h > +++ b/arch/x86/include/asm/irqflags.h > @@ -13,7 +13,7 @@ > * Interrupt control: > */ > > -static inline unsigned long native_save_fl(void) > +extern inline unsigned long native_save_fl(void) > { > unsigned long flags; > > diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile > index 02d6f5cf4e70..8824d01c0c35 100644 > --- a/arch/x86/kernel/Makefile > +++ b/arch/x86/kernel/Makefile > @@ -61,6 +61,7 @@ obj-y += alternative.o i8253.o hw_breakpoint.o > obj-y += tsc.o tsc_msr.o io_delay.o rtc.o > obj-y += pci-iommu_table.o > obj-y += resource.o > +obj-y += irqflags.o > > obj-y += process.o > obj-y += fpu/ > diff --git a/arch/x86/kernel/irqflags.S b/arch/x86/kernel/irqflags.S > new file mode 100644 > index 000000000000..ddeeaac8adda > --- /dev/null > +++ b/arch/x86/kernel/irqflags.S > @@ -0,0 +1,26 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > + > +#include <asm/asm.h> > +#include <asm/export.h> > +#include <linux/linkage.h> > + > +/* > + * unsigned long native_save_fl(void) > + */ > +ENTRY(native_save_fl) > + pushf > + pop %_ASM_AX > + ret > +ENDPROC(native_save_fl) > +EXPORT_SYMBOL(native_save_fl) > + > +/* > + * void native_restore_fl(unsigned long flags) > + * %eax/%rdi: flags > + */ > +ENTRY(native_restore_fl) > + push %_ASM_ARG1 > + popf > + ret > +ENDPROC(native_restore_fl) > +EXPORT_SYMBOL(native_restore_fl) > -- > 2.17.1.1185.g55be947832-goog > Probably should have mentioned in the notes/cover letter that this was rebased on hpa's patch (2/3) in this series. As a change from v2. -- Thanks, ~Nick Desaulniers -- To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
