Re: [PATCH kbuild v4] kbuild: add an elfnote for whether vmlinux is built with lto

From: Sedat Dilek <sedat.dilek@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Michal Marek <michal.lkml@markovi.net>,
	Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
	Alexei Starovoitov <ast@kernel.org>,
	Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com>,
	bpf <bpf@vger.kernel.org>, Kernel Team <kernel-team@fb.com>,
	Bill Wendling <morbo@google.com>,
	clang-built-linux <clang-built-linux@googlegroups.com>,
	Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH kbuild v4] kbuild: add an elfnote for whether vmlinux is built with lto
Date: Sun, 11 Apr 2021 20:09:34 +0200	[thread overview]
Message-ID: <CA+icZUXac=XVvyPDxvKHVpd2FWyTkBNp2zcFizA0DbCmfrDTUw@mail.gmail.com> (raw)
In-Reply-To: <d43d8804-ff30-fa38-b9d0-5dc20df2d795@fb.com>

On Sun, Apr 11, 2021 at 7:44 PM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 4/11/21 5:31 AM, Masahiro Yamada wrote:
> > On Wed, Apr 7, 2021 at 11:49 PM Yonghong Song <yhs@fb.com> wrote:
> >>
> >>
> >>
> >> On 4/7/21 6:46 AM, Arnaldo Carvalho de Melo wrote:
> >>> Em Tue, Apr 06, 2021 at 11:23:27PM -0700, Yonghong Song escreveu:
> >>>> On 4/6/21 8:01 PM, Sedat Dilek wrote:
> >>>>> On Tue, Apr 6, 2021 at 6:13 PM Yonghong Song <yhs@fb.com> wrote:
> >>>>>> Masahiro and Michal,
> >>>
> >>>>>> Friendly ping. Any comments on this patch?
> >>>
> >>>>>> The addition LTO .notes information emitted by kernel is used by pahole
> >>>>>> in the following patch:
> >>>>>>        https://lore.kernel.org/bpf/20210401025825.2254746-1-yhs@fb.com/
> >>>>>>        (dwarf_loader: check .notes section for lto build info)
> >>>
> >>>>> the above pahole patch has this define and comment:
> >>>
> >>>>> -static bool cus__merging_cu(Dwarf *dw)
> >>>>> +/* Match the define in linux:include/linux/elfnote.h */
> >>>>> +#define LINUX_ELFNOTE_BUILD_LTO 0x101
> >>>
> >>>>> ...and does not fit with the define and comment in this kernel patch:
> >>>
> >>>>> +#include <linux/elfnote.h>
> >>>>> +
> >>>>> +#define LINUX_ELFNOTE_LTO_INFO 0x101
> >>>
> >>>> Thanks, Sedat. I am aware of this. I think we can wait in pahole
> >>>> to make a change until the kernel patch is finalized and merged.
> >>>> The kernel patch may still change as we haven't get
> >>>> maintainer's comment. This will avoid unnecessary churn's
> >>>> in pahole side.
> >>>
> >>> So, I tested with clang 12 on fedora rawhide as well on fedora 33, and
> >>> I'm satisfied with the current state to release v1.21, Masahiro, have
> >>> you had the time to look at this?
> >>>
> >>> Yonghong, as we have a fallback in case the ELF note isn't available, I
> >>> think we're safe even if the notes patch merge gets delayed, right?
> >>
> >> Right. That is why I separated the notes patch from other patches.
> >> We can revisit it once the kernel patch is settled.
> >>
> >>>
> >>> - Arnaldo
> >>>
> >
> >
> > Applied to linux-kbuild. Thanks.
>
> Thanks!
>

Great to see this applied.
Thanks.

- Sedat -