linux-kernel - CONFIG_THUMB2_KERNEL=y boot failure after Spectre BHB fixes

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Message-ID: <YipOoAaBIHjeCKOq@dev-arch.thelio-3990X>
Date:   Thu, 10 Mar 2022 12:16:48 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Russell King <linux@...linux.org.uk>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        llvm@...ts.linux.dev
Subject: CONFIG_THUMB2_KERNEL=y boot failure after Spectre BHB fixes

Hi Russell,

Apologies if this has already been reported, I did not see anything when
sifting through lore.kernel.org and I can still reproduce this with
current mainline (1db333d9a51f).

I noticed a QEMU boot failure with multi_v7_defconfig with
CONFIG_THUMB2_KERNEL=y in our continuous integration [1]. It does not
appear to be compiler specific, as it reproduces with a bunch of
different clang versions and GCC 11.2.0 (I didn't try other GCC
versions).

At commit 04e91b732476 ("ARM: early traps initialisation"), everything
boots fine.

At commit 8d9d651ff227 ("ARM: use LOADADDR() to get load address of
sections"), there is no output from QEMU at all.

At commit b9baf5c8c5c3 ("ARM: Spectre-BHB workaround"), there is some
output but the boot still hangs before init. I have included a log of
the output of QEMU at this revision along with the command line I am
using, which comes from [2]. If I disable CONFIG_HARDEN_BRANCH_HISTORY,
the kernel boots.

If there is any further information I can provide or patches I can try,
I am happy to do so.

[1]: https://github.com/ClangBuiltLinux/continuous-integration2/runs/5496036256?check_suite_focus=true
[2]: https://github.com/ClangBuiltLinux/boot-utils

Cheers,
Nathan

View attachment "boot.log" of type "text/plain" (3897 bytes)