On March 4, 2017 4:14:47 PM PST, Borislav Petkov <b...@suse.de> wrote: >On Sat, Mar 04, 2017 at 03:55:27PM -0800, h...@zytor.com wrote: >> For newer processors, as determined by -mtune=, it is actually the >> best option for an arbitrary copy. > >So his doesn't have ERMS - it is a SNB - so if for SNB REP_GOOD is >the best option for memcpy, then we should probably build with >-fno-builtin-memcpy unconditionally. Otherwise gcc apparently inserts >its own memcpy variant. > >And this is probably wrong because we do the detection at boot time and >not at build time. > >For example here it generates REP; MOVSL for the call in >drivers/firmware/dmi_scan.c::dmi_scan_machine() which looks wrong to >me. >Length is 32 so it could just as well do REP; MOVSQ. > >IOW, we could do something like this: > >--- >diff --git a/arch/x86/Makefile b/arch/x86/Makefile >index 2d449337a360..c1b68d147b8d 100644 >--- a/arch/x86/Makefile >+++ b/arch/x86/Makefile >@@ -142,10 +142,7 @@ ifdef CONFIG_X86_X32 > endif > export CONFIG_X86_X32_ABI > >-# Don't unroll struct assignments with kmemcheck enabled >-ifeq ($(CONFIG_KMEMCHECK),y) >- KBUILD_CFLAGS += $(call cc-option,-fno-builtin-memcpy) >-endif >+KBUILD_CFLAGS += $(call cc-option,-fno-builtin-memcpy) > > # Stackpointer is addressed different for 32 bit and 64 bit x86 > sp-$(CONFIG_X86_32) := esp
What are the compilation flags? It may be that gcc still does TRT depending on this call site. I'd check what gcc6 or 7 generates, though. -- Sent from my Android device with K-9 Mail. Please excuse my brevity.
