All of lore.kernel.org
 help / color / mirror / Atom feed
From: Sedat Dilek <sedat.dilek@gmail.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>,
	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: Fri, 4 Mar 2022 12:42:54 +0100	[thread overview]
Message-ID: <CA+icZUXf9m13GrqvCLkDRsnQt0X2VQ=yVrJRYz=6fhCJXR4-Xg@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdkA1c3U6+-6hB3Nj9m2Z8eYzsFWm5X4se2eq_cF3NB2jA@mail.gmail.com>

On Thu, Mar 3, 2022 at 9:43 PM Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> 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
> > > +
>

I can remember on x86-64 I was able to build and boot by dropping it entirely.

- Sedat -

>
>
> --
> Thanks,
> ~Nick Desaulniers

WARNING: multiple messages have this Message-ID (diff)
From: Sedat Dilek <sedat.dilek@gmail.com>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Nathan Chancellor <nathan@kernel.org>,
	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: Fri, 4 Mar 2022 12:42:54 +0100	[thread overview]
Message-ID: <CA+icZUXf9m13GrqvCLkDRsnQt0X2VQ=yVrJRYz=6fhCJXR4-Xg@mail.gmail.com> (raw)
In-Reply-To: <CAKwvOdkA1c3U6+-6hB3Nj9m2Z8eYzsFWm5X4se2eq_cF3NB2jA@mail.gmail.com>

On Thu, Mar 3, 2022 at 9:43 PM Nick Desaulniers <ndesaulniers@google.com> wrote:
>
> 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
> > > +
>

I can remember on x86-64 I was able to build and boot by dropping it entirely.

- Sedat -

>
>
> --
> Thanks,
> ~Nick Desaulniers

_______________________________________________
linux-um mailing list
linux-um@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-um


  reply	other threads:[~2022-03-04 11:43 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
2022-03-03 18:39         ` Nick Desaulniers
2022-03-04 11:42         ` Sedat Dilek [this message]
2022-03-04 11:42           ` Sedat Dilek
2022-03-04  6:51   ` David Gow
2022-03-04  6:51     ` David Gow

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CA+icZUXf9m13GrqvCLkDRsnQt0X2VQ=yVrJRYz=6fhCJXR4-Xg@mail.gmail.com' \
    --to=sedat.dilek@gmail.com \
    --cc=anton.ivanov@cambridgegreys.com \
    --cc=davidgow@google.com \
    --cc=jdike@addtoit.com \
    --cc=keescook@chromium.org \
    --cc=kunit-dev@googlegroups.com \
    --cc=linux-hardening@vger.kernel.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-kselftest@vger.kernel.org \
    --cc=linux-um@lists.infradead.org \
    --cc=llvm@lists.linux.dev \
    --cc=masahiroy@kernel.org \
    --cc=nathan@kernel.org \
    --cc=ndesaulniers@google.com \
    --cc=richard@nod.at \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.