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Date: Wed, 24 Jun 2020 14:49:25 -0700
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Will Deacon <will@...nel.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"Paul E. McKenney" <paulmck@...nel.org>,
Kees Cook <keescook@...omium.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
clang-built-linux@...glegroups.com,
kernel-hardening@...ts.openwall.com, linux-arch@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-kbuild@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
x86@...nel.org
Subject: Re: [PATCH 05/22] kbuild: lto: postpone objtool
On Wed, Jun 24, 2020 at 11:19:08PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 24, 2020 at 01:31:43PM -0700, Sami Tolvanen wrote:
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index 30827f82ad62..12b115152532 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -120,7 +120,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
> > /* Annotate a C jump table to allow objtool to follow the code flow */
> > #define __annotate_jump_table __section(.rodata..c_jump_table)
> >
> > -#ifdef CONFIG_DEBUG_ENTRY
> > +#if defined(CONFIG_DEBUG_ENTRY) || defined(CONFIG_LTO_CLANG)
> > /* Begin/end of an instrumentation safe region */
> > #define instrumentation_begin() ({ \
> > asm volatile("%c0:\n\t" \
>
> Why would you be doing noinstr validation for lto builds? That doesn't
> make sense.
This is just to avoid a ton of noinstr warnings when we run objtool on
vmlinux.o, but I'm also fine with skipping noinstr validation with LTO.
> > +ifdef CONFIG_STACK_VALIDATION
> > +ifneq ($(SKIP_STACK_VALIDATION),1)
> > +cmd_ld_ko_o += \
> > + $(objtree)/tools/objtool/objtool \
> > + $(if $(CONFIG_UNWINDER_ORC),orc generate,check) \
> > + --module \
> > + $(if $(CONFIG_FRAME_POINTER),,--no-fp) \
> > + $(if $(CONFIG_GCOV_KERNEL),--no-unreachable,) \
> > + $(if $(CONFIG_RETPOLINE),--retpoline,) \
> > + $(if $(CONFIG_X86_SMAP),--uaccess,) \
> > + $(@:.ko=$(prelink-ext).o);
> > +
> > +endif # SKIP_STACK_VALIDATION
> > +endif # CONFIG_STACK_VALIDATION
>
> What about the objtool invocation from link-vmlinux.sh ?
What about it? The existing objtool_link invocation in link-vmlinux.sh
works fine for our purposes as well.
Sami
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