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Date: Sat, 30 Jan 2021 15:12:31 -0500
From: Rich Felker <dalias@...c.org>
To: Jiahao XU <Jiahao_XU@...look.com>
Cc: "musl@...ts.openwall.com" <musl@...ts.openwall.com>
Subject: Re: Can’t build musl with
lto=thin
On Fri, Jan 29, 2021 at 12:19:42PM +0000, Jiahao XU wrote:
> musl-1.2.2 compilation with clang-11 failed to build libc.so at the final linking stage:
>
> ld.lld: error: undefined hidden symbol: __dls2
> >>> referenced by ld-temp.o
> >>> lto.tmp:(_dlstart_c)
> >>> did you mean: __dls3
> >>> defined in: lto.tmp
>
> I am using CFLAGS=‘-march=native -mtune=native -Oz -flto
> -fmerge-all-constants -fomit-frame-pointer’ and LDFLAGS=‘-flto
^^^^^^^^^^^^^^^^^^^^^
The -fmerge-all-constants option gives non-conforming language
semantics and should not be used, but that's a separate issue.
> -fuse-ld=lld -Wl,—plugin-opt=O3,-O3,—icf=safe’.
> No configure option is supplied.
Otherwise, it's a known issue that LTO misses references from asm
(both top-level and in functions). I think dlstart.lo and a few other
files should just be built with LTO disabled; any LTO-type
optimization in code that runs at this stage is inherently invalid,
anyway. So something like (in config.mak):
obj/ldso/dlstart.lo: CFLAGS_ALL += -fno-lto
Rich
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