Bug 29540

Summary:	ld ppc64: unneeded R_PPC64_NONE in .rela.dyn when linking Linux vdso
Product:	binutils	Reporter:	Fangrui Song <maskray>
Component:	ld	Assignee:	Alan Modra <amodra>
Status:	RESOLVED FIXED
Severity:	normal
Priority:	P2
Version:	unspecified
Target Milestone:	2.40
Host:		Target:	powerpc64-linux
Build:		Last reconfirmed:
Project(s) to access:		ssh public key:

Description Fangrui Song 2022-08-30 20:14:21 UTC

This should be reproducible with many Linux versions, but I have just checked some recent commits, e.g. dcf8e5633e2e69ad60b730ab5905608b756a032f today

% git remote -v | grep origin
origin  https://github.com/torvalds/linux (fetch)
origin  https://github.com/torvalds/linux (push)
% make O=/tmp/linux/ppc64le ARCH=powerpc CROSS_COMPILE=powerpc64le-linux-gnu- -j60 defconfig all
% readelf -Wr /tmp/linux/ppc64le/arch/powerpc/kernel/vdso/vdso64.so.dbg

Relocation section '.rela.dyn' at offset 0x14f0 contains 4 entries:
    Offset             Info             Type               Symbol's Value  Symbol's Name + Addend
0000000000000000  0000000000000000 R_PPC64_NONE                              0
0000000000000000  0000000000000000 R_PPC64_NONE                              0
0000000000000000  0000000000000000 R_PPC64_NONE                              0
0000000000000000  0000000000000000 R_PPC64_NONE                              0

The linker script is innocent. I don't reproduce the problem with other ports (though I know that the riscv port produces R_RISCV_NONE in certain scenarios)

make O=/tmp/linux/x86_64 -j60 defconfig all && readelf -Wr /tmp/linux/x86_64/arch/x86/entry/vdso/vdso64.so
make O=/tmp/linux/aarch64 ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- LLVM=1 -j60 all && readelf -Wr /tmp/linux/aarch64/arch/arm64/kernel/vdso/vdso.so
make O=/tmp/linux/riscv64 ARCH=riscv CROSS_COMPILE=riscv64-linux-gnu- -j60 defconfig all && readelf -Wr /tmp/linux/riscv64/arch/riscv/kernel/vdso/vdso.so
make O=/tmp/linux/s390x ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- -j60 defconfig all && readelf -Wr /tmp/linux/s390x/arch/s390/kernel/vdso64/vdso64.so

Comment 1 Alan Modra 2022-09-10 03:23:06 UTC

Despite the use of a powerpc64le-linux compiler, defconfig builds an ELFv1 kernel not ELFv2.  So this is a powerpc64-linux problem triggerered by discarding .opd in the linker script.

Comment 2 Sourceware Commits 2022-09-14 00:50:22 UTC

The master branch has been updated by Alan Modra <amodra@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=365bf300da35c11e27bb8cdd3964f82e3d32f094

commit 365bf300da35c11e27bb8cdd3964f82e3d32f094
Author: Alan Modra <amodra@gmail.com>
Date:   Sat Sep 10 12:58:44 2022 +0930

    PR29540, R_PPC64_NONE in .rela.dyn when linking Linux vdso
    
            PR 29540
            * elf64-ppc.c (allocate_dynrelocs): Don't alloc space for relocs
            against discarded sections.
            (ppc64_elf_size_dynamic_sections): Use standard test for discarded
            sections.
            * elf32-ppc.c (allocate_dynrelocs): Don't alloc space for relocs
            against discarded sections.
            (ppc_elf_size_dynamic_sections): Use standard test for discarded
            sections.

Comment 3 Alan Modra 2022-09-14 02:33:03 UTC

Fixed for 2.40