ld.lld unknown relocation (110) against symbol for powerpc64

[nathanchance]

Just filing this from https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org/message/X43XFH7N4VREFNFWVMEUHJFFXD4QTWMG.

$ curl -LSs https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org/message/X43XFH7N4VREFNFWVMEUHJFFXD4QTWMG/attachment/2/config.gz | gzip -d > .config

$ make -skj"$(nproc)" ARCH=powerpc CC=clang CROSS_COMPILE=powerpc64-linux-gnu- LD=ld.lld olddefconfig vmlinux
ld.lld: error: arch/powerpc/built-in.a(kernel/exceptions-64e.o):(.text+0x22FE): unknown relocation (110) against symbol interrupt_base_book3e
ld.lld: error: arch/powerpc/built-in.a(kernel/exceptions-64e.o):(.text+0x2316): unknown relocation (110) against symbol __end_interrupts
ld.lld: error: arch/powerpc/built-in.a(kernel/exceptions-64e.o):(.text+0x248A): unknown relocation (110) against symbol interrupt_base_book3e
ld.lld: error: arch/powerpc/built-in.a(kernel/exceptions-64e.o):(.text+0x24A2): unknown relocation (110) against symbol __end_interrupts
ld.lld: error: arch/powerpc/built-in.a(kernel/exceptions-64e.o):(.text+0x36BA): unknown relocation (110) against symbol
ld.lld: error: undefined symbol: .early_setup
>>> referenced by arch/powerpc/kernel/head_64.o:(.ref.text+0x8E)
>>> did you mean: early_setup
>>> defined in: arch/powerpc/built-in.a(kernel/setup_64.o)

[nickdesaulniers]

Relocation number 110 is not listed in "Figure 4-1. Relocation Table" https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html#RELOC-TYPE cc @uweigand @MaskRay

I wonder if GAS is producing a new 64b relocation type?

[uweigand]

That ABI doc is outdated, the current version is now maintained by OpenPOWER. 110 is R_PPC64_ADDR16_HIGH, see: http://cdn.openpowerfoundation.org/wp-content/uploads/resources/leabi/content/ch03s05s03.html

[MaskRay]

https://refspecs.linuxfoundation.org/ELF/ppc64/PPC-elf64abi.html is what people usually refer to as ELF v1.

The OpenPower document is ELF v2.

I did not know #high (no overflow check) exists while there is also #hi (overflow check)... I'll implement it in LLD.

The relocation desugars from

LOAD_REG_IMMEDIATE_SYM(r14, r15, interrupt_base_book3e)

// arch/powerpc/include/asm/ppc_asm.h defines LOAD_REG_IMMEDIATE_SYM and __AS_ATHIGH

Clang generated code does not use @high as far as I can tell.

[nickdesaulniers]

thanks @MaskRay @uweigand