Re: [PATCH v2] arch: fix broken BuildID for arm64 and riscv

From: Michael Ellerman <mpe@ellerman.id.au>
To: Ard Biesheuvel <ardb@kernel.org>, Andreas Schwab <schwab@linux-m68k.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	linux-arch@vger.kernel.org, linux-kbuild@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Thorsten Leemhuis <regressions@leemhuis.info>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-riscv@lists.infradead.org, Dennis Gilmore <dennis@ausil.us>,
	Albert Ou <aou@eecs.berkeley.edu>, Arnd Bergmann <arnd@arndb.de>,
	Jisheng Zhang <jszhang@kernel.org>,
	Nicolas Schier <nicolas@fjasle.eu>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	llvm@lists.linux.dev
Subject: Re: [PATCH v2] arch: fix broken BuildID for arm64 and riscv
Date: Thu, 05 Jan 2023 22:14:20 +1100	[thread overview]
Message-ID: <87y1qh2pyr.fsf@mpe.ellerman.id.au> (raw)
In-Reply-To: <CAMj1kXGD3wQUPsRhvD7bO9xBJ6NR=Z+y8wXmKSCs57Oeh3MzGw@mail.gmail.com>

Ard Biesheuvel <ardb@kernel.org> writes:
> On Thu, 5 Jan 2023 at 10:21, Andreas Schwab <schwab@linux-m68k.org> wrote:
>> On Jan 05 2023, Masahiro Yamada wrote:
>>
>> > I do not understand why 99cb0d917ffa affected this.
>> >
>> >
>> > I submitted a fix to shoot the error message "discarded section .exit.text"
>> >
>> > https://lore.kernel.org/all/20230105031306.1455409-1-masahiroy@kernel.org/T/#u
>> >
>> > I do not understand the binutils commit either,
>> > but it might have made something good
>> > because EXIT_TEXT appears twice, in .exit.text, and /DISCARD/.
>>
>> I think the issue is that the introdution of a second /DISCARD/
>> directive early in script changes the order of evaluation of the other
>> /DISCARD/ directive when binutils < 2.36 is used, so that the missing
>> RUNTIME_DISCARD_EXIT started to become relevant.  As long as /DISCARD/
>> only appears last, the effect of EXIT_TEXT inside it is always
>> overridden by its occurence in the .exit.exit output section directive.
>> When another /DISCARD/ occurs early (and binutils < 2.36 is used) the
>> effect of EXIT_TEXT inside the second /DISCARD/ (when merged with the
>> first) overrides its occurence in the .exit.text directive.  The
>> binutils commit changed that because the new /DISCARD/ directive no
>> longer affects the order of evaluation of the rest of the directives.
>>
>
> Exactly. The binutils change mentions output section merging, which
> apparently applies to the /DISCARD/ pseudo section as well.
>
> However, powerpc was also affected by this, and I suggested another
> fix in the thread below
>
> https://lore.kernel.org/all/20230103014535.GA313835@roeck-us.net/

I'm working on powerpc fixes, which I think are all improvements
regardless of whether your change in the above thread is merged or not.

I'll try and get them posted tonight.

cheers