Date: Fri, 18 Oct 2019 10:32:20 -0700 From: Nick Desaulniers <ndesaulniers@...gle.com> To: Sami Tolvanen <samitolvanen@...gle.com> Cc: Will Deacon <will@...nel.org>, Catalin Marinas <catalin.marinas@....com>, Steven Rostedt <rostedt@...dmis.org>, Ard Biesheuvel <ard.biesheuvel@...aro.org>, Dave Martin <Dave.Martin@....com>, Kees Cook <keescook@...omium.org>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, clang-built-linux <clang-built-linux@...glegroups.com>, kernel-hardening@...ts.openwall.com, Linux ARM <linux-arm-kernel@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 05/18] arm64: kbuild: reserve reg x18 from general allocation by the compiler On Fri, Oct 18, 2019 at 9:11 AM Sami Tolvanen <samitolvanen@...gle.com> wrote: > > From: Ard Biesheuvel <ard.biesheuvel@...aro.org> > > Before we can start using register x18 for a special purpose (as permitted > by the AAPCS64 ABI), we need to tell the compiler that it is off limits > for general allocation. So tag it as 'fixed', yep, but... > and remove the mention from > the LL/SC compiler flag override. was that cut/dropped from this patch? > > Link: https://patchwork.kernel.org/patch/9836881/ ^ Looks like it. Maybe it doesn't matter, but if sending a V2, maybe the commit message to be updated? > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org> > Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com> If sending a V2 with the above cleaned up, you may also include: Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com> I like how this does not conditionally reserve it based on the CONFIG for SCS. Hopefully later patches don't wrap it, but I haven't looked through all of them yet. > --- > arch/arm64/Makefile | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile > index 2c0238ce0551..1c7b276bc7c5 100644 > --- a/arch/arm64/Makefile > +++ b/arch/arm64/Makefile > @@ -55,7 +55,7 @@ endif > > KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst) \ > $(compat_vdso) $(cc_has_k_constraint) > -KBUILD_CFLAGS += -fno-asynchronous-unwind-tables > +KBUILD_CFLAGS += -fno-asynchronous-unwind-tables -ffixed-x18 > KBUILD_CFLAGS += $(call cc-disable-warning, psabi) > KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) $(compat_vdso) > > -- > 18.104.22.1686.gb869b98d4c-goog > -- Thanks, ~Nick Desaulniers
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