Date: Fri, 27 Feb 2026 16:24:13 -0500 From: John Baldwin <jhb@FreeBSD.org> To: Mark Millard <marklmi@yahoo.com>, Jessica Clarke <jrtc27@freebsd.org> Cc: "dev-commits-src-all@freebsd.org" <dev-commits-src-all@FreeBSD.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@FreeBSD.org>, Andrew Turner <andrew@FreeBSD.org> Subject: Re: git: ee73475119ff - main - llvm: Link private LLVM libraries against compiler_rt for aarch64 Message-ID: <f1e53a2a-5b73-46bc-a664-3e6d387be3a4@FreeBSD.org> In-Reply-To: <720e4cb6-fd13-4686-93d9-ef095ad611c2@yahoo.com> References: <698a0b1e.1d294.40e36519@gitrepo.freebsd.org> <E1734CF0-E6FC-40B8-BAD0-DE2269756E2E@freebsd.org> <c9039150-1bb1-4466-9142-9e9ad560c73a@FreeBSD.org> <23acebb1-f71c-46e6-9eea-3fa44316335d@FreeBSD.org> <720e4cb6-fd13-4686-93d9-ef095ad611c2@yahoo.com>
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On 2/27/26 15:55, Mark Millard wrote: > On 2/27/26 09:27, John Baldwin wrote: >> On 2/9/26 11:47, John Baldwin wrote: >>> On 2/9/26 11:40, Jessica Clarke wrote: >>>> On 9 Feb 2026, at 16:28, John Baldwin <jhb@FreeBSD.org> wrote: >>>>> >>>>> The branch main has been updated by jhb: >>>>> >>>>> URL: https://cgit.FreeBSD.org/src/commit/? >>>>> id=ee73475119ff7aa98bd11828625d524f6ab87f06 >>>>> >>>>> commit ee73475119ff7aa98bd11828625d524f6ab87f06 >>>>> Author: John Baldwin <jhb@FreeBSD.org> >>>>> AuthorDate: 2026-02-09 16:26:52 +0000 >>>>> Commit: John Baldwin <jhb@FreeBSD.org> >>>>> CommitDate: 2026-02-09 16:26:52 +0000 >>>>> >>>>> llvm: Link private LLVM libraries against compiler_rt for aarch64 >>>>> >>>>> This is required for GCC which uses libcalls for outlined atomics. >>>> >>>> This doesn’t seem right, they’re provided by libgcc.a, so why aren’t >>>> they being pulled in? libcompiler_rt.a doesn’t even have the symbols. >>> >>> My guess is that we don't link libraries against libgcc by default, only >>> binaries (maybe this is a GCC feature/bug vs clang)? I have another >>> review >>> open for a couple of google test libraries which similarly fail to link. >> >> So after some more digging (along with Jessica), it seems that GCC only >> uses -lgcc_s (and not -lgcc) for C++ (but not C) on both Linux and FreeBSD. >> clang's FreeBSD toolchain driver is supposed to mimic GCC but doesn't, it >> applies the C rules even for C++ linking, so clang is implicitly adding >> both -lgcc and -lgcc_s for C++. >> >> On Linux, libgcc.so is a linker script that includes both the dynamic >> library and -lgcc which is how the static libgcc (including outline atomics >> for aarch64) is effectively linked into C++ shared libraries on Linux. >> (Note: libgcc.so is a linker script on seemingly all arches on Linux, not >> just aarch64) >> >> So I think we have a couple of choices here. I can patch the devel/ >> freebsd-gccN >> ports to stop passing -shared-libgcc to cc1plus which will cause GCC to >> follow >> the same rules as clang on FreeBSD (passing -lgcc -as-needed -lgcc_s - >> no-as-needed >> instead of -lgcc_s), or we could change libgcc.so to be a linker script >> to match >> Linux (and then eventually fix the FreeBSD driver in clang to only pass >> -lgcc_s for C++ linking) (I think Andrew already has a review to make >> libgcc.so >> a linker script). >> >> I can see arguments both ways. Using a linker script seems kind of dumb >> given >> all the hoops GCC goes to internally to decide whether or not to link only >> shared or static or both. (Esp given libgcc is in theory part of the >> compiler, >> so the compiler should know that libgcc_s should depend on libgcc and be >> able >> to encode that in the default drivers.) OTOH, the linker script >> approach would >> mean we would more closely align with Linux. I think Jess favors >> patching GCC. >> Does anyone else have any strong opinions? >> > > Is the question limited to devel/freebsd-gcc* ? Or does it span > lang/gcc* use as well? We don't really support building the base system with lang/gcc* (it's why devel/freebsd-gcc* exist) as the base system builds require various changes like kernel printf support, defaulting to libc++, etc. -- John Baldwinhome | help
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