cmd/link/internal/ld: work around FreeBSD 14.1 cmd/cgo test link failure

On FreeBSD 14.1 we fail to link against C code with internal linking.
The symptom is apparently undefined symbols, but explicitly pointing the
linker at compiler-rt for -libgcc fixes the issue. This looks a lot like
the workaround on OpenBSD, but the symptom is different.
--print-libgcc-file-name produces libclang_rt.builtins-x86_64.a which
appears to be an insufficient subset of libcompiler_rt.a.

For #61095.

Change-Id: Iff5affbc923d69c89d671a69d8f4ecaadac42177
Cq-Include-Trybots: luci.golang.try:gotip-freebsd-amd64
Reviewed-on: https://go-review.googlesource.com/c/go/+/632975
Auto-Submit: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Michael Knyszek <mknyszek@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

diff --git a/src/cmd/link/internal/ld/lib.go b/src/cmd/link/internal/ld/lib.go
index 0d38593ec72b2afb25c6bfc37c878f66bbfd14d4..2d8f964f3594c6d8ae66fd6a91024dd41315cb70 100644 (file)
--- a/src/cmd/link/internal/ld/lib.go
+++ b/src/cmd/link/internal/ld/lib.go
@@ -632,6 +632,13 @@ func (ctxt *Link) loadlib() {
                        if *flagLibGCC == "" {
                                *flagLibGCC = ctxt.findLibPathCmd("--print-libgcc-file-name", "libgcc")
                        }
+                       if runtime.GOOS == "freebsd" && strings.HasPrefix(filepath.Base(*flagLibGCC), "libclang_rt.builtins") {
+                               // On newer versions of FreeBSD, libgcc is returned as something like
+                               // /usr/lib/clang/18/lib/freebsd/libclang_rt.builtins-x86_64.a.
+                               // Unfortunately this ends up missing a bunch of symbols we need from
+                               // libcompiler_rt.
+                               *flagLibGCC = ctxt.findLibPathCmd("--print-file-name=libcompiler_rt.a", "libcompiler_rt")
+                       }
                        if runtime.GOOS == "openbsd" && *flagLibGCC == "libgcc.a" {
                                // On OpenBSD `clang --print-libgcc-file-name` returns "libgcc.a".
                                // In this case we fail to load libgcc.a and can encounter link