Date: Mon, 27 Apr 2026 18:05:45 -0700 From: Mark Millard <marklmi@yahoo.com> To: John Baldwin <jhb@FreeBSD.org>, Andrew Turner <andrew@FreeBSD.org>, dev-commits-src-all@FreeBSD.org, dev-commits-src-main@FreeBSD.org Subject: Re: git: e63eee84cad5 - main - libgcc_s: Add a linker script to link to libgcc Message-ID: <cd2ba351-68d6-4186-95ce-714959721ade@yahoo.com> In-Reply-To: <30459007-56a1-4edf-8b20-2921e8e2e420@FreeBSD.org> References: <69ef4ad1.1c7d4.4b8c5d49@gitrepo.freebsd.org> <30459007-56a1-4edf-8b20-2921e8e2e420@FreeBSD.org>
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On 4/27/26 06:52, John Baldwin wrote: > On 4/27/26 07:38, Andrew Turner wrote: >> The branch main has been updated by andrew: >> >> URL: https://cgit.FreeBSD.org/src/commit/? >> id=e63eee84cad59f63338a539e73bed07917932088 >> >> commit e63eee84cad59f63338a539e73bed07917932088 >> Author: Andrew Turner <andrew@FreeBSD.org> >> AuthorDate: 2026-04-27 10:54:18 +0000 >> Commit: Andrew Turner <andrew@FreeBSD.org> >> CommitDate: 2026-04-27 11:37:53 +0000 >> >> libgcc_s: Add a linker script to link to libgcc >> When using outline atomics on arm64 the compiler will create >> a call to >> a function that performs the atomic operation. This allows us to use >> the fastest operation depending on the hardware. >> As these functions are implemented in libgcc create a linker >> script >> so libraries that link against libgcc_s will include libgcc to pull >> them in. > > Some additional notes: > > GCC only links with -lgcc_s (the shared library) when linking C++ > executables > and libraries, but links with both -lgcc_s and -lgcc when linking C > executables > and libraries. clang does the same on most libgcc-using platforms like > Linux, > except that for FreeBSD, clang treats C++ like C and links in both > libraries > (this is probably an accidental bug in clang's FreeBSD toolchain driver, > but > kind of moot). Linux distributions use an ldscript for libgcc_s on all > architectures (not just aarch64) to handle this weirdness of GCC. > > This is all pretty sad as GCC ships with libgcc and should "know" if > libgcc_s > needs symbols from libgcc, but matching Linux is probably the path of least > friction going forward. An oddity is that the lang/gcc*'s libgcc_s.so.1 and the FreeBSD system libgcc_s.so.1 do not match, FreeBSD having many symbols missing compared to GCC --and the other way around as well. It can be required to use something like -Wl,-rpath=... to force use of the appropriate lang/gcc*'s libgcc_s.so when using the gcc* or g++* compiler in order to avoid failures from missing symbols. modern amd64 examples are listed in: <https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294110>; modern aarch64 examples are listed in: <https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294109>; There are also mismatches like (aarch64 context): (-: FreeBSD OS, +: lang/gcc15) +GCC_4.5.0 __unordtf2 -GCC_4.6.0 __unordtf2 and: +GCC_3.0 __addtf3 -GCC_4.6.0 __addtf3 Even: int main() { } compiled/linked via g++15 gets: # ./trivial ld-elf.so.1: /lib/libgcc_s.so.1: version GCC_4.5.0 required by /usr/local/lib/gcc15/libstdc++.so.6 not found So there is more to the mismatches in this general area than just -lgcc being used vs. not. (I've never checked for -lgcc mismatches.) > It would only be worth fixing the toolchain driver > in clang if it meant removing the custom libgcc code, but I suspect we will > always need it for existing FreeBSD versions, so it's not clear to me > that it is > worth doing. > -- === Mark Millard marklmi at yahoo.comhome | help
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