linux-kernel - Re: [PATCH 7/7] modpost: detect section mismatch for R_ARM

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Message-ID: <CAK7LNATDJmh1aas86YW4yrG_8Rqgz7r82NwaPj1x5c7tg-d-jg@mail.gmail.com>
Date:   Thu, 1 Jun 2023 23:35:47 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Russell King <linux@...linux.org.uk>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>
Subject: Re: [PATCH 7/7] modpost: detect section mismatch for R_ARM_REL32

On Thu, Jun 1, 2023 at 9:40 PM Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Thu, 1 Jun 2023 at 14:10, Masahiro Yamada <masahiroy@...nel.org> wrote:
> >
> > For ARM, modpost fails to detect some types of section mismatches.
> >
> >   [test code]
> >
> >     .section .init.data,"aw"
> >     bar:
> >             .long 0
> >
> >     .section .data,"aw"
> >     .globl foo
> >     foo:
> >             .long bar - .
> >
> > It is apparently a bad reference, but modpost does not report anything.
> >
> > The test code above produces the following relocations.
> >
> >   Relocation section '.rel.data' at offset 0xe8 contains 1 entry:
> >    Offset     Info    Type            Sym.Value  Sym. Name
> >   00000000  00000403 R_ARM_REL32       00000000   .init.data
> >
> > Currently, R_ARM_REL32 is just skipped.
> >
> > Handle it like R_ARM_ABS32.
>
> OK, so the reason we can handle these in the same way is because we
> never calculate the resulting value, right? Because that value would
> be different for these cases.

Right.

'- loc' is unnecessary here because modpost never calculates the
resulting instruction.

modpost wants to know the location of the referenced symbol.
(the offset from the start of the section).

For the same reason, I omitted '- loc' for
PC-relative ones such as R_ARM_CALL, R_ARM_JUMP24, etc.







--
Best Regards

Masahiro Yamada