Re: Regression: commit 987fdfec2410 causes build to incorrectly issue warning

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Catalin Marinas <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
	Masahiro Yamada <masahiroy@kernel.org>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: Regression: commit 987fdfec2410 causes build to incorrectly issue warning
Date: Fri, 2 Jul 2021 15:48:33 +0100	[thread overview]
Message-ID: <20210702144833.GO22278@shell.armlinux.org.uk> (raw)
In-Reply-To: <20210702131301.GD1350@shell.armlinux.org.uk>

On Fri, Jul 02, 2021 at 02:13:01PM +0100, Russell King - ARM Linux admin wrote:
> Hi,
> 
> Commit 987fdfec2410 ("arm64: move --fix-cortex-a53-843419 linker test to
> Kconfig") breaks the ability to detect linker support for this option.
> Building 5.13 for aarch64 with Debian binutils 2.31.1 results in:
> 
> .../arch/arm64/Makefile:25: ld does not support --fix-cortex-a53-843419; kernel may be susceptible to erratum
> 
> This is because ARM64_LD_HAS_FIX_ERRATUM_843419 is not set in the
> Kconfig, indicating that the Kconfig test for linker support for
> --fix-cortex-a53-843419 has failed, yet this version of binutils does
> support this option:
> 
> $ aarch64-linux-gnu-ld --help | grep -e --fix-cortex-a53-843419 | wc -l
> 8
> 
> Reverting this commit fixes the problem for me.

Sadly, while reverting the commit fixes it during the initial build
run, the warning pops up when doing the installation step.

I'm not entirely sure what's going on here. Having put the commit
back, and re-run strace (and waited ages) it appears that the
ld-option command does succeed, and I eventually end up with the
option present in .config.

However, it seems that if we have a .config that has the errata
enabled, but doesn't contain the _LD_ option, then we end up issuing
the warning before we re-run the Kconfig step.

Eventually, I seem to have ended up with the _LD_ option set. Quite
how, I don't know. When I originally noticed the problem, I had done
a full rebuild. I then re-ran the build several times, and the warning
popped up every time.

Now that I've touched arch/arm64/Kconfig and re-run the build, it
doesn't warn anymore - in fact, while investigating this and stracing,
the option magically set itself and the problem has vanished.

There is definitely weirdness and unpredictability going on with
Kbuild - I can't explain it. Maybe its just become way to complex...

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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