linux-kernel - Re: [PATCH] arm64 module: remove (NOLOAD)

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Date:   Fri, 18 Feb 2022 09:34:22 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Fangrui Song <maskray@...gle.com>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        llvm@...ts.linux.dev
Subject: Re: [PATCH] arm64 module: remove (NOLOAD)

On Fri, Feb 18, 2022 at 12:50:16AM -0800, Fangrui Song wrote:
> On 2022-02-18, Ard Biesheuvel wrote:
> > On Fri, 18 Feb 2022 at 09:12, Fangrui Song <maskray@...gle.com> wrote:
> > > 
> > > On ELF, (NOLOAD) sets the section type to SHT_NOBITS[1]. It is conceptually
> > > inappropriate for .plt and .text.* sections which are always
> > > SHT_PROGBITS.
> > > 
> > > In GNU ld, if PLT entries are needed, .plt will be SHT_PROGBITS anyway
> > > and (NOLOAD) will be essentially ignored. In ld.lld, since
> > > https://reviews.llvm.org/D118840 ("[ELF] Support (TYPE=<value>) to
> > > customize the output section type"), ld.lld will report a `section type
> > > mismatch` error. Just remove (NOLOAD) to fix the error.
> > > 
> > > [1] https://lld.llvm.org/ELF/linker_script.html As of today, "The
> > > section should be marked as not loadable" on
> > > https://sourceware.org/binutils/docs/ld/Output-Section-Type.html is
> > > outdated for ELF.
> > 
> > This patch lacks a SOB line.
> > 
> > With one added,
> > 
> > Acked-by: Ard Biesheuvel <ardb@...nel.org>
> 
> Ah, yes. Sorry, I haven't sent a kernel patch for a while...
> 
> Reported-by: Nathan Chancellor <nathan@...nel.org>
> Signed-off-by: Fangrui Song <maskray@...gle.com>
> Acked-by: Ard Biesheuvel <ardb@...nel.org>

I am assuming this patch is the solution we want, as opposed to Ard's
suggestion of renaming these sections at
https://reviews.llvm.org/D118840 (unless that was a tangential
suggestion).

I have verified that modules still load. Additionally, this needs to go
to stable so that groups who upgrade their toolchain to a revision that
include the LLD patch don't get broken as well.

Cc: stable@...r.kernel.org
Tested-by: Nathan Chancellor <nathan@...nel.org>


> > > ---
> > >  arch/arm64/include/asm/module.lds.h | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/arch/arm64/include/asm/module.lds.h b/arch/arm64/include/asm/module.lds.h
> > > index a11ccadd47d2..094701ec5500 100644
> > > --- a/arch/arm64/include/asm/module.lds.h
> > > +++ b/arch/arm64/include/asm/module.lds.h
> > > @@ -1,8 +1,8 @@
> > >  SECTIONS {
> > >  #ifdef CONFIG_ARM64_MODULE_PLTS
> > > -       .plt 0 (NOLOAD) : { BYTE(0) }
> > > -       .init.plt 0 (NOLOAD) : { BYTE(0) }
> > > -       .text.ftrace_trampoline 0 (NOLOAD) : { BYTE(0) }
> > > +       .plt 0 : { BYTE(0) }
> > > +       .init.plt 0 : { BYTE(0) }
> > > +       .text.ftrace_trampoline 0 : { BYTE(0) }
> > >  #endif
> > > 
> > >  #ifdef CONFIG_KASAN_SW_TAGS
> > > --
> > > 2.35.1.265.g69c8d7142f-goog
> > > 
>