linux-kernel - Re: [PATCH v2] powerpc: Handle .text.{hot,unlikely}.* in linker script

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Date:   Sat, 16 Jan 2021 11:52:47 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Paul Mackerras <paulus@...ba.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2] powerpc: Handle .text.{hot,unlikely}.* in linker
 script

On Sat, Jan 16, 2021 at 12:44:38PM -0600, Segher Boessenkool wrote:
> Hi!
> 
> Very late of course, and the patch is fine, but:
> 
> On Mon, Jan 04, 2021 at 01:59:53PM -0700, Nathan Chancellor wrote:
> > Commit eff8728fe698 ("vmlinux.lds.h: Add PGO and AutoFDO input
> > sections") added ".text.unlikely.*" and ".text.hot.*" due to an LLVM
> > change [1].
> > 
> > After another LLVM change [2], these sections are seen in some PowerPC
> > builds, where there is a orphan section warning then build failure:
> > 
> > $ make -skj"$(nproc)" \
> >        ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- LLVM=1 O=out \
> >        distclean powernv_defconfig zImage.epapr
> > ld.lld: warning: kernel/built-in.a(panic.o):(.text.unlikely.) is being placed in '.text.unlikely.'
> 
> Is the section really called ".text.unlikely.", i.e. the name ending in
> a dot?  How very unusual, is there some bug elsewhere?

No, this was an intention change done by LLVM:
https://reviews.llvm.org/D79600

Cheers,
Nathan