linux-kernel - Re: [PATCH] [RFC, DO NOT APPLY] vmlinux.lds: revert link speed regression

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Message-Id: <04db1d00-8801-4d29-bed9-54b2cc39e4fc@app.fastmail.com>
Date: Wed, 22 Jan 2025 21:29:51 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Rong Xu" <xur@...gle.com>
Cc: "Arnd Bergmann" <arnd@...nel.org>, linux-kbuild@...r.kernel.org,
 "Masahiro Yamada" <masahiroy@...nel.org>, linux-kernel@...r.kernel.org,
 regressions@...ts.linux.dev, "Han Shen" <shenhan@...gle.com>,
 "Nathan Chancellor" <nathan@...nel.org>, "Kees Cook" <kees@...nel.org>,
 "Jann Horn" <jannh@...gle.com>, "Ard Biesheuvel" <ardb@...nel.org>,
 Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] [RFC, DO NOT APPLY] vmlinux.lds: revert link speed regression

On Wed, Jan 22, 2025, at 19:47, Rong Xu wrote:
> On Tue, Jan 21, 2025 at 1:18 PM Arnd Bergmann <arnd@...db.de> wrote:
>>
>> On Tue, Jan 21, 2025, at 18:45, Rong Xu wrote:
>> > On Mon, Jan 20, 2025 at 1:29 PM Arnd Bergmann <arnd@...nel.org> wrote:
>> >
>> > Yes. The order could be conditional. As a matter of fact, the first
>> > version was conditional.
>> > I changed it based on the reviewer comments to reduce conditions for
>> > more maintainable code.
>> > I would like to work from the ld.bfd side to see if we can fix the problem.
>>
>> Makes sense. At least once we understand what makes the linker so slow
>> and fix future versions, it should also be possible to come up with
>> a more effective workaround for the existing linkers that suffer from it.
>
> @Arnd: Can you send me the instructions to reproduce this regression?

My report had linked to the config that I saw originally:

>> > Link: https://pastebin.com/raw/sWpbkapL (config)

This is for a x86_64 build, and I used 'make savedefconfig' to
simplify it, so you have to copy it to arch/x86/configs/test_defconfig
and run 'make test_defconfig' to get the full file back.

I have also uploaded a reproducer to
https://drive.google.com/file/d/14xWdD_S51XBgV6kOajLvdtOef7tQTZQq/view?usp=sharing
but it's fairly large. The reproducer is from ld.lld --reproduce=, but
you can simply unpack it and do

x86_64-linux-gnu-ld.bfd  -m elf_x86_64 -z noexecstack --emit-relocs --discard-none -z max-page-size=0x200000 --gc-sections --build-id=sha1 --orphan-handling warn --script home/arnd/arm-soc/build/x86/0xA8B23FFD_defconfig/arch/x86/kernel/vmlinux.lds --strip-debug -o .tmp_vmlinux1 --whole-archive home/arnd/arm-soc/build/x86/0xA8B23FFD_defconfig/vmlinux.a home/arnd/arm-soc/build/x86/0xA8B23FFD_defconfig/init/version-timestamp.o --no-whole-archive --start-group home/arnd/arm-soc/build/x86/0xA8B23FFD_defconfig/lib/lib.a home/arnd/arm-soc/build/x86/0xA8B23FFD_defconfig/arch/x86/lib/lib.a --end-group home/arnd/arm-soc/build/x86/0xA8B23FFD_defconfig/.tmp_vmlinux0.kallsyms.o

    Arnd