From: qmuntal Date: Wed, 22 Oct 2025 14:33:18 +0000 (+0200) Subject: cmd/link: support weak binding on darwin X-Git-Tag: go1.26rc1~360 X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=8cf7a0b4c956aad5a8b98efde8ea6b7cde173902;p=gostls13.git cmd/link: support weak binding on darwin Symbols loaded from host files can have the N_WEAK_REF bit set, which is used to instruct the loader to not fail if that symbol can't be resolved. The Go internal linker should honor this information by setting the BIND_SYMBOL_FLAGS_WEAK_IMPORT flag in the corresponding bind table entry. Fixes #76023 Cq-Include-Trybots: luci.golang.try:gotip-darwin-amd64-longtest,gotip-darwin-amd64_12,gotip-darwin-arm64_12,gotip-darwin-arm64_15,gotip-darwin-arm64-longtest,gotip-darwin-amd64_14 Change-Id: Id2cef247ec7a9cb08455844f3c30ff874772bb7b Reviewed-on: https://go-review.googlesource.com/c/go/+/713760 Reviewed-by: Michael Knyszek Reviewed-by: Michael Pratt LUCI-TryBot-Result: Go LUCI --- diff --git a/src/cmd/cgo/internal/test/cgo_darwin_test.go b/src/cmd/cgo/internal/test/cgo_darwin_test.go new file mode 100644 index 0000000000..5d9d164002 --- /dev/null +++ b/src/cmd/cgo/internal/test/cgo_darwin_test.go @@ -0,0 +1,11 @@ +// Copyright 2025 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +//go:build cgo && darwin + +package cgotest + +import "testing" + +func TestIssue76023(t *testing.T) { issue76023(t) } diff --git a/src/cmd/cgo/internal/test/issue76023.go b/src/cmd/cgo/internal/test/issue76023.go new file mode 100644 index 0000000000..7fe8ae53f7 --- /dev/null +++ b/src/cmd/cgo/internal/test/issue76023.go @@ -0,0 +1,27 @@ +// Copyright 2025 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +//go:build darwin + +package cgotest + +/* +#cgo LDFLAGS: -Wl,-undefined,dynamic_lookup + +extern void __gotest_cgo_null_api(void) __attribute__((weak_import)); + +int issue76023(void) { + if (__gotest_cgo_null_api) return 1; + return 0; +} +*/ +import "C" +import "testing" + +func issue76023(t *testing.T) { + r := C.issue76023() + if r != 0 { + t.Error("found __gotest_cgo_null_api") + } +} diff --git a/src/cmd/link/internal/ld/macho.go b/src/cmd/link/internal/ld/macho.go index 6d3347ff2d..65ae1268c3 100644 --- a/src/cmd/link/internal/ld/macho.go +++ b/src/cmd/link/internal/ld/macho.go @@ -180,6 +180,8 @@ const ( BIND_SPECIAL_DYLIB_FLAT_LOOKUP = -2 BIND_SPECIAL_DYLIB_WEAK_LOOKUP = -3 + BIND_SYMBOL_FLAGS_WEAK_IMPORT = 0x1 + BIND_OPCODE_MASK = 0xF0 BIND_IMMEDIATE_MASK = 0x0F BIND_OPCODE_DONE = 0x00 @@ -1429,7 +1431,11 @@ func machoDyldInfo(ctxt *Link) { bind.AddUint8(BIND_OPCODE_SET_DYLIB_SPECIAL_IMM | uint8(d)&0xf) } - bind.AddUint8(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM) + flags := uint8(0) + if ldr.SymWeakBinding(r.targ) { + flags |= BIND_SYMBOL_FLAGS_WEAK_IMPORT + } + bind.AddUint8(BIND_OPCODE_SET_SYMBOL_TRAILING_FLAGS_IMM | flags) // target symbol name as a C string, with _ prefix bind.AddUint8('_') bind.Addstring(ldr.SymExtname(r.targ)) diff --git a/src/cmd/link/internal/loader/loader.go b/src/cmd/link/internal/loader/loader.go index 3fb2e86514..a612a1ac81 100644 --- a/src/cmd/link/internal/loader/loader.go +++ b/src/cmd/link/internal/loader/loader.go @@ -241,6 +241,7 @@ type Loader struct { plt map[Sym]int32 // stores dynimport for pe objects got map[Sym]int32 // stores got for pe objects dynid map[Sym]int32 // stores Dynid for symbol + weakBinding map[Sym]bool // stores whether a symbol has a weak binding relocVariant map[relocId]sym.RelocVariant // stores variant relocs @@ -326,6 +327,7 @@ func NewLoader(flags uint32, reporter *ErrorReporter) *Loader { plt: make(map[Sym]int32), got: make(map[Sym]int32), dynid: make(map[Sym]int32), + weakBinding: make(map[Sym]bool), attrCgoExportDynamic: make(map[Sym]struct{}), attrCgoExportStatic: make(map[Sym]struct{}), deferReturnTramp: make(map[Sym]bool), @@ -1447,6 +1449,18 @@ func (l *Loader) SetSymExtname(i Sym, value string) { } } +func (l *Loader) SymWeakBinding(i Sym) bool { + return l.weakBinding[i] +} + +func (l *Loader) SetSymWeakBinding(i Sym, v bool) { + // reject bad symbols + if i >= Sym(len(l.objSyms)) || i == 0 { + panic("bad symbol index in SetSymWeakBinding") + } + l.weakBinding[i] = v +} + // SymElfType returns the previously recorded ELF type for a symbol // (used only for symbols read from shared libraries by ldshlibsyms). // It is not set for symbols defined by the packages being linked or diff --git a/src/cmd/link/internal/loadmacho/ldmacho.go b/src/cmd/link/internal/loadmacho/ldmacho.go index 5e8022ce69..dcb0fd92c1 100644 --- a/src/cmd/link/internal/loadmacho/ldmacho.go +++ b/src/cmd/link/internal/loadmacho/ldmacho.go @@ -613,6 +613,9 @@ func Load(l *loader.Loader, arch *sys.Arch, localSymVersion int, f *bio.Reader, } if machsym.desc&(N_WEAK_REF|N_WEAK_DEF) != 0 { l.SetAttrDuplicateOK(s, true) + if machsym.desc&N_WEAK_REF != 0 { + l.SetSymWeakBinding(s, true) + } } machsym.sym = s if machsym.sectnum == 0 { // undefined