linux-kernel - Re: [PATCH v1] ARM: vfp: Use long jump to fix THUMB2 kernel compilation error

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Message-ID: <20201022145734.GO1551@shell.armlinux.org.uk>
Date:   Thu, 22 Oct 2020 15:57:35 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Kees Cook <keescook@...omium.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v1] ARM: vfp: Use long jump to fix THUMB2 kernel
 compilation error

On Thu, Oct 22, 2020 at 01:57:37AM +0300, Dmitry Osipenko wrote:
> The vfp_kmode_exception() function now is unreachable using relative
> branching in THUMB2 kernel configuration, resulting in a "relocation
> truncated to fit: R_ARM_THM_JUMP19 against symbol `vfp_kmode_exception'"
> linker error. Let's use long jump in order to fix the issue.
> 
> Fixes: eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input sections")
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>

I guess the problem is that vfp_support_entry is in .text which tends
to be at the beginning of the text section, but vfp_kmode_exception
is in something like .text.vfp_kmode_exception ?

Would it be an idea just to change the section name that stuff like
vfp_support_entry ends up in, rather than making the code less
efficient?

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