go: cmd/link: Go c-archive doesn't work with new Xcode 15 beta ld-prime linker

We found that Go libraries (-buildmode=c-archive) linked into iOS apps crash on startup (during the dynamic loader?) when using the new Xcode 15 beta’s “ld-prime” linker.

The workaround for now is to force the old linker with LDFLAGS=-ld64, so filing this issue for people to find.

/cc @agottardo (who figured out the workaround and can probably provide more details)

About this issue

Original URL
State: closed
Created a year ago
Reactions: 5
Comments: 21 (10 by maintainers)

Commits related to this issue

cmd/link: don't generate DYSYMTAB when external linking on Mach-O When external linking, the external linker will generate it. Updates #60694. For #61229. Change-Id: I086a7628dd9baa84b46315641746fc... — committed to golang/go by cherrymui a year ago
[release-branch.go1.21] cmd/link: don't generate DYSYMTAB when external linking on Mach-O When external linking, the external linker will generate it. Updates #60694. For #61229. Change-Id: I086a76... — committed to golang/go by cherrymui a year ago
cmd/link: always use symbol-targeted relocations on Mach-O In Mach-O object files, there are two kinds of relocations: "external" relocation, which targets a symbol, and "non-external" relocation, wh... — committed to golang/go by cherrymui a year ago
[release-branch.go1.21] cmd/link: don't generate DYSYMTAB when external linking on Mach-O When external linking, the external linker will generate it. Updates #60694. For #61229. Change-Id: I086a76... — committed to tailscale/go by cherrymui a year ago
[release-branch.go1.21] cmd/link: use symbol-targeted relocation for initializers on Mach-O Apple's new linker, ld-prime from Xcode 15 beta, when handling initializers in __mod_init_func, drops the o... — committed to golang/go by cherrymui a year ago

Most upvoted comments

This hack seems to make it work. Basically, for __mod_init_func, we need to use symbol-targeted relocation, instead of section+offset-targeted relocation (ld-prime just drops the offset, making it point to the start of the section…)… This seems to work for both ld64 and ld-prime.

diff --git a/src/cmd/link/internal/amd64/asm.go b/src/cmd/link/internal/amd64/asm.go
index 7082c839ee..58b29fb6ea 100644
--- a/src/cmd/link/internal/amd64/asm.go
+++ b/src/cmd/link/internal/amd64/asm.go
@@ -469,7 +469,7 @@ func machoreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sy
        rs := r.Xsym
        rt := r.Type
 
-       if ldr.SymType(rs) == sym.SHOSTOBJ || rt == objabi.R_PCREL || rt == objabi.R_GOTPCREL || rt == objabi.R_CALL {
+       if ldr.SymType(rs) == sym.SHOSTOBJ || rt == objabi.R_PCREL || rt == objabi.R_GOTPCREL || rt == objabi.R_CALL || ldr.SymType(s) == sym.SINITARR {
                if ldr.SymDynid(rs) < 0 {
                        ldr.Errorf(s, "reloc %d (%s) to non-macho symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
                        return false
diff --git a/src/cmd/link/internal/arm64/asm.go b/src/cmd/link/internal/arm64/asm.go
index f2a2b32232..2c3c994169 100644
--- a/src/cmd/link/internal/arm64/asm.go
+++ b/src/cmd/link/internal/arm64/asm.go
@@ -580,7 +580,7 @@ func machoreloc1(arch *sys.Arch, out *ld.OutBuf, ldr *loader.Loader, s loader.Sy
        if ldr.SymType(rs) == sym.SHOSTOBJ || rt == objabi.R_CALLARM64 ||
                rt == objabi.R_ARM64_PCREL_LDST8 || rt == objabi.R_ARM64_PCREL_LDST16 ||
                rt == objabi.R_ARM64_PCREL_LDST32 || rt == objabi.R_ARM64_PCREL_LDST64 ||
-               rt == objabi.R_ADDRARM64 || rt == objabi.R_ARM64_GOTPCREL {
+               rt == objabi.R_ADDRARM64 || rt == objabi.R_ARM64_GOTPCREL || ldr.SymType(s) == sym.SINITARR {
                if ldr.SymDynid(rs) < 0 {
                        ldr.Errorf(s, "reloc %d (%s) to non-macho symbol %s type=%d (%s)", rt, sym.RelocName(arch, rt), ldr.SymName(rs), ldr.SymType(rs), ldr.SymType(rs))
                        return false
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index d651e2e346..891d7c7358 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -368,7 +368,7 @@ func (st *relocSymState) relocsym(s loader.Sym, P []byte) {
                                                o = 0
                                        }
                                } else if target.IsDarwin() {
-                                       if ldr.SymType(rs) != sym.SHOSTOBJ {
+                                       if ldr.SymType(rs) != sym.SHOSTOBJ && ldr.SymType(s) != sym.SINITARR {
                                                o += ldr.SymValue(rs)
                                        }
                                } else if target.IsWindows() {

cherrymui on Jun 10, 2023

@albertoAround the fix will be included in Go 1.21, which is to be released next week. You could also checkout the master branch and build the Go toolchain (you could also cherry-pick CL https://golang.org/cl/502616 but it is probably better and simpler to just use the master branch). Thanks.

cherrymui on Aug 2, 2023

@agottardo Thanks for sharing. I’ll look into it.

Also, I downloaded Xcode 15 beta, ran it on a macOS ARM64 machine using ld-prime with Go, and found a number of issues. While some of them are minor, I got SIGILL for the c-shared and plugin mode, which may also be related. I’ll look into them. Thanks.

cherrymui on Jun 8, 2023