linux-kernel - Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA

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Message-Id: <58297ee9-4f33-4b3b-bd00-b44e86965892@app.fastmail.com>
Date: Thu, 22 Feb 2024 17:04:43 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Yuntao Liu" <liuyuntao12@...wei.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: "Russell King" <linux@...linux.org.uk>, "Andrew Davis" <afd@...com>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 "Geert Uytterhoeven" <geert+renesas@...der.be>,
 "Jonathan Corbet" <corbet@....net>, "Mike Rapoport" <rppt@...nel.org>,
 "Eric DeVolder" <eric.devolder@...cle.com>, "Rob Herring" <robh@...nel.org>,
 "Thomas Gleixner" <tglx@...utronix.de>,
 "Linus Walleij" <linus.walleij@...aro.org>
Subject: Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

On Thu, Feb 22, 2024, at 12:24, liuyuntao (F) wrote:
>
> The position of the caret has been moved below the right brace
> of { KEEP(*(.vectors.bhb.loop8)) }, indicating that lld is treating
> the entire `KEEP(*(.vectors))` as a file name. This could potentially be 
> a bug in lld. Perhaps we can temporarily
> enable the DCE option only when option LD_IS_LLD is disabled,
> like risc-v:
>
> `select HAVE_LD_DEAD_CODE_DATA_ELIMINATION if !LD_IS_LLD`.

I would really like to see this working with lld if at all
possible, as it allows the combination of gc-sections with
lto and CONFIG_TRIM_UNUSED_KSYMS.

I experimented with lld myself now and I did get a booting
kernel even without the the KEEP() on the vectors. I also
see that this is the only use of OVERLAY in the kernel, so
I hope that we can find a way to make it work with existing
lld after all, either without the KEEP or without the OVERLAY.

Did you see any problems without the KEEP() on the vectors?

     Arnd