Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

From: "Arnd Bergmann" <arnd@arndb.de>
To: "Yuntao Liu" <liuyuntao12@huawei.com>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Cc: "Russell King" <linux@armlinux.org.uk>,
	"Andrew Davis" <afd@ti.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Jonathan Corbet" <corbet@lwn.net>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Eric DeVolder" <eric.devolder@oracle.com>,
	"Rob Herring" <robh@kernel.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Linus Walleij" <linus.walleij@linaro.org>
Subject: Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION
Date: Thu, 22 Feb 2024 17:04:43 +0100	[thread overview]
Message-ID: <58297ee9-4f33-4b3b-bd00-b44e86965892@app.fastmail.com> (raw)
In-Reply-To: <4e9396ca-460b-49ca-818e-73f0a8997b15@huawei.com>

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