linux-kernel - [PATCH v5 0/5] Allow ld.lld to link the MIPS VDSO

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Date:   Tue, 28 Apr 2020 15:14:14 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Masahiro Yamada <masahiroy@...nel.org>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com, linux-kbuild@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Dmitry Golovin <dima@...ovin.in>,
        Sedat Dilek <sedat.dilek@...il.com>
Subject: [PATCH v5 0/5] Allow ld.lld to link the MIPS VDSO

Hi all,

This series allows ld.lld to properly and completely link the MIPS vDSO.

Patch 1 adds ld.lld support to Kconfig so that we can avoid certain
ld.bfd checks.

Patch 2 moves disabling of the VDSO to Kconfig. This allows us to avoid
a warning with LD=ld.lld during the clean phase, when we do not have
access to CONFIG_LD_IS_LLD.

Patch 3 prepares for the shift from $(CC) to $(LD) and is probably a
worthwhile change aside from this series because GCC 4.6 is the minimum
version allowed to build the kernel.

Patch 4 does the actual shift from $(CC) to $(LD) to link the VDSO.

Patch 5 allows LD=ld.lld to build the VDSO fully through Kconfig.

I have build tested 32r2_defconfig, 32r2el_defconfig, 64r2_defconfig,
and 64r2el_defconfig with GCC and 32r2el_defconfig and
malta_kvm_guest_defconfig with clang. There is a separate issue with the
64-bit configs (https://github.com/ClangBuiltLinux/linux/issues/884) and
ld.lld does not support the triple OUTPUT_FORMAT linker script macro so
32r2_defconfig errors out in a manner similar to GCC without patch 3:
https://github.com/llvm/llvm-project/blob/46a75436f811d0e6a2c76c669140a7e9471cd2a3/lld/ELF/ScriptParser.cpp#L430
TODO: File an LLVM bug upstream

Please let me know if there are any issues!

Cheers,
Nathan