cmd/link: disable DWARF by default in c-shared mode on darwin

Currently, linking a Go c-shared object with C code using Apple's
new linker, it fails with

% cc a.c go.so
ld: segment '__DWARF' filesize exceeds vmsize in 'go.so'

Apple's new linker has more checks for unmapped segments. It is
very hard to make it accept a Mach-O shared object with an
additional DWARF segment.

We may want to stop combinding DWARF into the shared object (see
also #62577). For now, disable DWARF by default in c-shared mode
on darwin. (One can still enable it with -ldflags=-w=0, which will
contain DWARF, but it will need the old C linker to link against
with.)

For #61229.

Change-Id: I4cc77da54fac10e2c2cbcffa92779cba82706d75
Reviewed-on: https://go-review.googlesource.com/c/go/+/527415
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/cmd/link/internal/ld/main.go b/src/cmd/link/internal/ld/main.go
index ccc7d29bf25ef7331d399000a3388a4ece7a5076..aa6c00ce88d9c1eb3359ff7762782825b316c4d2 100644 (file)
--- a/src/cmd/link/internal/ld/main.go
+++ b/src/cmd/link/internal/ld/main.go
@@ -245,6 +245,9 @@ func Main(arch *sys.Arch, theArch Arch) {
                *FlagW = true
        case ternaryFlagUnset:
                *FlagW = *FlagS // -s implies -w if not explicitly set
+               if ctxt.IsDarwin() && ctxt.BuildMode == BuildModeCShared {
+                       *FlagW = true // default to -w in c-shared mode on darwin, see #61229
+               }
        }
 
        if !buildcfg.Experiment.RegabiWrappers {