| Message ID | 20200819191654.1130563-5-ndesaulniers@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | -ffreestanding/-fno-builtin-* patches | expand |
On Wed, Aug 19, 2020 at 12:16:53PM -0700, Nick Desaulniers wrote: > We're reverting > commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") > in favor of -fno-builtin-bcmp. Remove the additional definition here, > too. > > arch/x86/purgatory/Makefile uses -ffreestanding, so there's no risk of > this libcall optimization occurring for arch/x86/boot/purgatory.ro. > > arch/x86/boot/Makefile resets KBUILD_CFLAGS, so make sure to reset this > flag that was set for the top level Makefile. > > Fixes: 4ce97317f41d ("x86/purgatory: Do not use __builtin_memcpy and __builtin_memset") > Reviewed-by: Kees Cook <keescook@chromium.org> > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > --- > arch/x86/boot/Makefile | 1 + > arch/x86/boot/string.c | 8 -------- > 2 files changed, 1 insertion(+), 8 deletions(-) > > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile > index fe605205b4ce..ef7f15bfceab 100644 > --- a/arch/x86/boot/Makefile > +++ b/arch/x86/boot/Makefile > @@ -70,6 +70,7 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP > KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ > KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > +KBUILD_CFLAGS += -fno-builtin-bcmp > GCOV_PROFILE := n > UBSAN_SANITIZE := n > This should be unnecessary: KBUILD_CFLAGS in arch/x86/boot/Makefile is set to REALMODE_CFLAGS (defined in arch/x86/Makefile), which includes -ffreestanding.
On Wed, Aug 19, 2020 at 12:29 PM Arvind Sankar <nivedita@alum.mit.edu> wrote: > > On Wed, Aug 19, 2020 at 12:16:53PM -0700, Nick Desaulniers wrote: > > We're reverting > > commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") > > in favor of -fno-builtin-bcmp. Remove the additional definition here, > > too. > > > > arch/x86/purgatory/Makefile uses -ffreestanding, so there's no risk of > > this libcall optimization occurring for arch/x86/boot/purgatory.ro. > > > > arch/x86/boot/Makefile resets KBUILD_CFLAGS, so make sure to reset this > > flag that was set for the top level Makefile. > > > > Fixes: 4ce97317f41d ("x86/purgatory: Do not use __builtin_memcpy and __builtin_memset") > > Reviewed-by: Kees Cook <keescook@chromium.org> > > Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> > > --- > > arch/x86/boot/Makefile | 1 + > > arch/x86/boot/string.c | 8 -------- > > 2 files changed, 1 insertion(+), 8 deletions(-) > > > > diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile > > index fe605205b4ce..ef7f15bfceab 100644 > > --- a/arch/x86/boot/Makefile > > +++ b/arch/x86/boot/Makefile > > @@ -70,6 +70,7 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP > > KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ > > KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) > > KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > > +KBUILD_CFLAGS += -fno-builtin-bcmp > > GCOV_PROFILE := n > > UBSAN_SANITIZE := n > > > > This should be unnecessary: KBUILD_CFLAGS in arch/x86/boot/Makefile is > set to REALMODE_CFLAGS (defined in arch/x86/Makefile), which includes > -ffreestanding. I triple checked by grepping the disassemblies of ./arch/x86/purgatory/purgatory.ro, arch/x86/purgatory/*.o, and arch/x86/boot/*.o for bcmp; should be fine to drop that hunk. Will wait a bit to see if there's other feedback, and whether folks are on board with the plan to merge the series proposed in the cover letter or not. -- Thanks, ~Nick Desaulniers
diff --git a/arch/x86/boot/Makefile b/arch/x86/boot/Makefile index fe605205b4ce..ef7f15bfceab 100644 --- a/arch/x86/boot/Makefile +++ b/arch/x86/boot/Makefile @@ -70,6 +70,7 @@ KBUILD_CFLAGS := $(REALMODE_CFLAGS) -D_SETUP KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ KBUILD_CFLAGS += $(call cc-option,-fmacro-prefix-map=$(srctree)/=) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables +KBUILD_CFLAGS += -fno-builtin-bcmp GCOV_PROFILE := n UBSAN_SANITIZE := n diff --git a/arch/x86/boot/string.c b/arch/x86/boot/string.c index 8a3fff9128bb..23d91aa7691e 100644 --- a/arch/x86/boot/string.c +++ b/arch/x86/boot/string.c @@ -37,14 +37,6 @@ int memcmp(const void *s1, const void *s2, size_t len) return diff; } -/* - * Clang may lower `memcmp == 0` to `bcmp == 0`. - */ -int bcmp(const void *s1, const void *s2, size_t len) -{ - return memcmp(s1, s2, len); -} - int strcmp(const char *str1, const char *str2) { const unsigned char *s1 = (const unsigned char *)str1;
We're reverting commit 5f074f3e192f ("lib/string.c: implement a basic bcmp") in favor of -fno-builtin-bcmp. Remove the additional definition here, too. arch/x86/purgatory/Makefile uses -ffreestanding, so there's no risk of this libcall optimization occurring for arch/x86/boot/purgatory.ro. arch/x86/boot/Makefile resets KBUILD_CFLAGS, so make sure to reset this flag that was set for the top level Makefile. Fixes: 4ce97317f41d ("x86/purgatory: Do not use __builtin_memcpy and __builtin_memset") Reviewed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Nick Desaulniers <ndesaulniers@google.com> --- arch/x86/boot/Makefile | 1 + arch/x86/boot/string.c | 8 -------- 2 files changed, 1 insertion(+), 8 deletions(-)