linux-kernel - Re: [PATCH] kbuild: Fix Propeller build option

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Message-ID: <CAF1bQ=Rh51kUaNk3zQbPAe6H_buNv3jU9kcyMmJ8csXbZYQqWQ@mail.gmail.com>
Date: Fri, 8 Nov 2024 10:49:56 -0800
From: Rong Xu <xur@...gle.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nicolas Schier <nicolas@...sle.eu>, 
	Han Shen <shenhan@...gle.com>, Nick Desaulniers <ndesaulniers@...gle.com>, 
	Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, linux-kbuild@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] kbuild: Fix Propeller build option

Nathan, thank you a lot for helping with the patch!

I will send an updated patch that integrates your suggestion shortly.

-Rong

On Fri, Nov 8, 2024 at 9:46 AM Nathan Chancellor <nathan@...nel.org> wrote:
>
> Hi Rong,
>
> Thanks for the quick patch!
>
> On Thu, Nov 07, 2024 at 09:10:30PM -0800, Rong Xu wrote:
> > The '-fbasic-block-sections=labels' option has been deprecated with
> > the following llvm patch:
> > https://github.com/llvm/llvm-project/pull/110039
> >
> > The old option still works, but with a warning like
> >   clang: warning: argument '-fbasic-block-sections=labels' \
> >   is deprecated, use '-fbasic-block-address-map' instead [-Wdeprecated]
> >
> > Currently, the option change is only in the ToT clang (v20) and not yet
> > released in v19.
>
> I think this whole block could be a little easier to read and understand
> with some more standard kernel commit message practices. I would combine
> the first and third block into one sentence and I would unwrap the
> warning text (it is okay to be long for a little clarity). Perhaps
> something like this?
>
>   | The '-fbasic-block-sections=labels' option has been deprecated in tip of
>   | tree clang (20.0.0) [1]. While the option still works, a warning is
>   | emitted:
>   |
>   |   clang: warning: argument '-fbasic-block-sections=labels' is deprecated, use '-fbasic-block-address-map' instead [-Wdeprecated]
>
> then putting:
>
>   | Link: https://github.com/llvm/llvm-project/pull/110039 [1]
>
> right above your Signoff.
>
> > This patch adds a check to the Makefile to set the proper option.
>
> Try to avoid saying "this patch" in kernel commit messages, it is
> implicit. It would be cleaner to say something like:
>
>   | Add a version check to set the proper option.
>
> You can see some more commit message tips in sections 4.2.3 to 4.2.6 in
> the tip documentation:
>
> https://docs.kernel.org/process/maintainer-tip.html#changelog
>
> > If the option change is later integrated in v19.x, we need to update the
> > check accordingly.
>
> I think it is worth dropping this sentence entirely, as I would argue
> that it is pretty unlikely that this option gets backported to
> release/19.x, since it would basically accelerate the deprecation
> timeline, which seems unreasonable to do in a stable release.
>

These are excellent suggestions that make the message more clear.
I'll update the patch description.

> > Signed-off-by: Rong Xu <xur@...gle.com>
> > Reported-by: Nathan Chancellor <nathan@...nel.org>
> > ---
> >  scripts/Makefile.propeller | 14 ++++++++++++--
> >  1 file changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/scripts/Makefile.propeller b/scripts/Makefile.propeller
> > index 344190717e47..1a68ea0d1fe4 100644
> > --- a/scripts/Makefile.propeller
> > +++ b/scripts/Makefile.propeller
> > @@ -5,7 +5,13 @@ ifdef CLANG_PROPELLER_PROFILE_PREFIX
> >    CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=list=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt -ffunction-sections
> >    KBUILD_LDFLAGS += --symbol-ordering-file=$(CLANG_PROPELLER_PROFILE_PREFIX)_ld_profile.txt --no-warn-symbol-ordering
> >  else
> > -  CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=labels
> > +  # Staring with clang v20, the '-fbasic-block-sections=labels' option is
> > +  # deprecated. Use the recommended '-fbasic-block-address-map' option.
>
> Might be worth linking the specific change here for archeology sake.
>

I will add the link in the comments.

> > +  ifeq ($(call clang-min-version, 200000),y)
> > +    CFLAGS_PROPELLER_CLANG := -fbasic-block-address-map
> > +  else
> > +    CFLAGS_PROPELLER_CLANG := -fbasic-block-sections=labels
> > +  endif
> >  endif
> >
> >  # Propeller requires debug information to embed module names in the profiles.
> > @@ -21,7 +27,11 @@ ifdef CONFIG_LTO_CLANG_THIN
> >    ifdef CLANG_PROPELLER_PROFILE_PREFIX
> >      KBUILD_LDFLAGS += --lto-basic-block-sections=$(CLANG_PROPELLER_PROFILE_PREFIX)_cc_profile.txt
> >    else
> > -    KBUILD_LDFLAGS += --lto-basic-block-sections=labels
> > +    ifeq ($(call clang-min-version, 200000),y)
>
> Would it be better/more accurate to check the LLD version here? I doubt
> it would really happen but it is possible for someone to have LLVM=1
> (using their system wide ld.lld and LLVM tools) and CC=clang-20 to just
> use an updated clang. Perhaps:
>
>   ifeq ($(call test-ge, $(CONFIG_LLD_VERSION), 200000),y)
>
> here?

I agree: checking the LLD version makes more sense here.

>
> > +       KBUILD_LDFLAGS += --lto-basic-block-address-map
> > +    else
> > +       KBUILD_LDFLAGS += --lto-basic-block-sections=labels
> > +    endif
> >    endif
> >  endif
> >
> >
> > base-commit: 0dcc2d1066150787017a71f035145c566597dec7
> > --
> > 2.47.0.277.g8800431eea-goog
> >