From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
David Gow <davidgow@google.com>, Jeff Dike <jdike@addtoit.com>,
Richard Weinberger <richard@nod.at>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>,
Masahiro Yamada <masahiroy@kernel.org>,
linux-um@lists.infradead.org, linux-kbuild@vger.kernel.org,
linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com,
llvm@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH] um: clang: Strip out -mno-global-merge from USER_CFLAGS
Date: Thu, 3 Mar 2022 10:39:58 -0800 [thread overview]
Message-ID: <CAKwvOdkA1c3U6+-6hB3Nj9m2Z8eYzsFWm5X4se2eq_cF3NB2jA@mail.gmail.com> (raw)
In-Reply-To: <YiEISsoS/XrbEtbm@thelio-3990X>
On Thu, Mar 3, 2022 at 10:26 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> On Thu, Mar 03, 2022 at 10:04:28AM -0800, Kees Cook wrote:
> > How does -mno-global-merge get KBUILD_CFLAGS in the first place? If it's
> > arm/arm64 only, shouldn't that get relocated to those architectures?
> >
> > *time travel* found it:
> >
> > 61163efae020 ("kbuild: LLVMLinux: Add Kbuild support for building kernel with Clang")
> >
> > So I think this may have been universally true long ago, and now only
> > arm/arm64 need it?
Looks like that's the case from LLVM sources.
<snip>
> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> > index a2391b8de5a5..dcab28c44c26 100644
> > --- a/arch/arm/Makefile
> > +++ b/arch/arm/Makefile
> > @@ -48,6 +48,13 @@ CHECKFLAGS += -D__ARMEL__
> > KBUILD_LDFLAGS += -EL
> > endif
> >
> > +ifdef CONFIG_CC_IS_CLANG
> > +# CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
> > +# source of a reference will be _MergedGlobals and not on of the whitelisted names.
I think there's a typo in the original comment.
s/on of/one of/ ?
Also, I'm not sure what's meant by _MergedGlobals. Perhaps this is an
opportunity to make this clearer?
"Clang's "global-merge" pass (implemented only for arm and aarch64)
may break modpost Pattern 2 if symbols are renamed and thus don't
appear on modpost's allowlist.
> > +# See modpost pattern 2
> > +KBUILD_CFLAGS += -mno-global-merge
> > +endif
> > +
--
Thanks,
~Nick Desaulniers
WARNING: multiple messages have this Message-ID (diff)
From: Nick Desaulniers <ndesaulniers@google.com>
To: Nathan Chancellor <nathan@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
David Gow <davidgow@google.com>, Jeff Dike <jdike@addtoit.com>,
Richard Weinberger <richard@nod.at>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>,
Masahiro Yamada <masahiroy@kernel.org>,
linux-um@lists.infradead.org, linux-kbuild@vger.kernel.org,
linux-kselftest@vger.kernel.org, kunit-dev@googlegroups.com,
llvm@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH] um: clang: Strip out -mno-global-merge from USER_CFLAGS
Date: Thu, 3 Mar 2022 10:39:58 -0800 [thread overview]
Message-ID: <CAKwvOdkA1c3U6+-6hB3Nj9m2Z8eYzsFWm5X4se2eq_cF3NB2jA@mail.gmail.com> (raw)
In-Reply-To: <YiEISsoS/XrbEtbm@thelio-3990X>
On Thu, Mar 3, 2022 at 10:26 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> On Thu, Mar 03, 2022 at 10:04:28AM -0800, Kees Cook wrote:
> > How does -mno-global-merge get KBUILD_CFLAGS in the first place? If it's
> > arm/arm64 only, shouldn't that get relocated to those architectures?
> >
> > *time travel* found it:
> >
> > 61163efae020 ("kbuild: LLVMLinux: Add Kbuild support for building kernel with Clang")
> >
> > So I think this may have been universally true long ago, and now only
> > arm/arm64 need it?
Looks like that's the case from LLVM sources.
<snip>
> > diff --git a/arch/arm/Makefile b/arch/arm/Makefile
> > index a2391b8de5a5..dcab28c44c26 100644
> > --- a/arch/arm/Makefile
> > +++ b/arch/arm/Makefile
> > @@ -48,6 +48,13 @@ CHECKFLAGS += -D__ARMEL__
> > KBUILD_LDFLAGS += -EL
> > endif
> >
> > +ifdef CONFIG_CC_IS_CLANG
> > +# CLANG uses a _MergedGlobals as optimization, but this breaks modpost, as the
> > +# source of a reference will be _MergedGlobals and not on of the whitelisted names.
I think there's a typo in the original comment.
s/on of/one of/ ?
Also, I'm not sure what's meant by _MergedGlobals. Perhaps this is an
opportunity to make this clearer?
"Clang's "global-merge" pass (implemented only for arm and aarch64)
may break modpost Pattern 2 if symbols are renamed and thus don't
appear on modpost's allowlist.
> > +# See modpost pattern 2
> > +KBUILD_CFLAGS += -mno-global-merge
> > +endif
> > +
--
Thanks,
~Nick Desaulniers
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next prev parent reply other threads:[~2022-03-03 18:40 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-03 9:06 [PATCH] um: clang: Strip out -mno-global-merge from USER_CFLAGS David Gow
2022-03-03 9:06 ` David Gow
2022-03-03 17:30 ` Nathan Chancellor
2022-03-03 17:30 ` Nathan Chancellor
2022-03-03 18:04 ` Kees Cook
2022-03-03 18:26 ` Nathan Chancellor
2022-03-03 18:26 ` Nathan Chancellor
2022-03-03 18:39 ` Nick Desaulniers [this message]
2022-03-03 18:39 ` Nick Desaulniers
2022-03-04 11:42 ` Sedat Dilek
2022-03-04 11:42 ` Sedat Dilek
2022-03-04 6:51 ` David Gow
2022-03-04 6:51 ` David Gow
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