linux-kernel - Re: linux-next: build failure after merge of most trees

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Message-ID: <20170622184116.0ebaabd9@roar.ozlabs.ibm.com>
Date:   Thu, 22 Jun 2017 18:41:16 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Stephen Rothwell <sfr@...b.auug.org.au>
Cc:     David Miller <davem@...emloft.net>,
        Linux-Next Mailing List <linux-next@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Alan Modra <amodra@...il.com>
Subject: Re: linux-next: build failure after merge of most trees

CC'ing Alan

On Thu, 22 Jun 2017 15:24:41 +1000
Stephen Rothwell <sfr@...b.auug.org.au> wrote:

> Hi Dave,
> 
> After merging almost all the trees, today's linux-next build (sparc64
> defconfig) failed like this:
> 
> arch/sparc/lib/hweight.o: In function `__arch_hweight8':
> (.text+0x0): relocation truncated to fit: R_SPARC_WDISP19 against symbol `__sw_hweight8' defined in .text section in lib/hweight.o
> arch/sparc/lib/hweight.o: In function `__arch_hweight16':
> (.text+0xc): relocation truncated to fit: R_SPARC_WDISP19 against symbol `__sw_hweight16' defined in .text section in lib/hweight.o
> arch/sparc/lib/hweight.o: In function `__arch_hweight32':
> (.text+0x18): relocation truncated to fit: R_SPARC_WDISP19 against symbol `__sw_hweight32' defined in .text section in lib/hweight.o
> arch/sparc/lib/hweight.o: In function `__arch_hweight64':
> (.text+0x24): relocation truncated to fit: R_SPARC_WDISP19 against symbol `__sw_hweight64' defined in .text section in lib/hweight.o

After a bit of digging, this is due to that thin archives patch, but only
because it changes the order of linker inputs around slightly. You can
reproduce it with upstream kernel:

This is the final link which succeeds:

sparc64-linux-gnu-ld -m elf64_sparc --build-id -o vmlinux -T ./arch/sparc/kernel/vmlinux.lds arch/sparc/kernel/head_64.o init/built-in.o --start-group usr/built-in.o arch/sparc/built-in.o kernel/built-in.o certs/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o lib/lib.a arch/sparc/prom/lib.a arch/sparc/lib/lib.a lib/built-in.o arch/sparc/prom/built-in.o arch/sparc/lib/built-in.o drivers/built-in.o sound/built-in.o firmware/built-in.o net/built-in.o virt/built-in.o --end-group .tmp_kallsyms2.o

Moving the lib.a files to the end:

sparc64-linux-gnu-ld -m elf64_sparc --build-id -o vmlinux -T ./arch/sparc/kernel/vmlinux.lds arch/sparc/kernel/head_64.o init/built-in.o --start-group usr/built-in.o arch/sparc/built-in.o kernel/built-in.o certs/built-in.o mm/built-in.o fs/built-in.o ipc/built-in.o security/built-in.o crypto/built-in.o block/built-in.o lib/built-in.o arch/sparc/prom/built-in.o arch/sparc/lib/built-in.o drivers/built-in.o sound/built-in.o firmware/built-in.o net/built-in.o virt/built-in.o lib/lib.a arch/sparc/prom/lib.a arch/sparc/lib/lib.a --end-group .tmp_kallsyms2.o

arch/sparc/lib/lib.a(hweight.o): In function `__arch_hweight8':
(.text+0x0): relocation truncated to fit: R_SPARC_WDISP19 against symbol `__sw_hweight8' defined in .text section in lib/built-in.o

If we also move lib/built-in.o to the end, then the error goes away.

Is there any way for the linker to place the inputs to avoid unresolvable
relocations where possible?

A way to work around this is to make arch/sparc/lib/hweight.o an obj-y
rather than lib-y. That's a hack because it just serves to move the
input location, but not really any more of a hack than the current code
that also only works because of input locations...

Any thoughts?

Thanks,
Nick