1 files changed, 67 insertions, 0 deletions
diff --git a/src/cmd/link/internal/ld/errors.go b/src/cmd/link/internal/ld/errors.go
new file mode 100644
index 0000000..b553d68
--- /dev/null
+++ b/src/cmd/link/internal/ld/errors.go
@@ -0,0 +1,67 @@
+// Copyright 2020 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.
+
+package ld
+
+import (
+	"cmd/internal/obj"
+	"cmd/link/internal/loader"
+	"cmd/link/internal/sym"
+	"sync"
+)
+
+type unresolvedSymKey struct {
+	from loader.Sym // Symbol that referenced unresolved "to"
+	to   loader.Sym // Unresolved symbol referenced by "from"
+}
+
+type symNameFn func(s loader.Sym) string
+
+// ErrorReporter is used to make error reporting thread safe.
+type ErrorReporter struct {
+	loader.ErrorReporter
+	unresSyms  map[unresolvedSymKey]bool
+	unresMutex sync.Mutex
+	SymName    symNameFn
+}
+
+// errorUnresolved prints unresolved symbol error for rs that is referenced from s.
+func (reporter *ErrorReporter) errorUnresolved(ldr *loader.Loader, s, rs loader.Sym) {
+	reporter.unresMutex.Lock()
+	defer reporter.unresMutex.Unlock()
+
+	if reporter.unresSyms == nil {
+		reporter.unresSyms = make(map[unresolvedSymKey]bool)
+	}
+	k := unresolvedSymKey{from: s, to: rs}
+	if !reporter.unresSyms[k] {
+		reporter.unresSyms[k] = true
+		name := ldr.SymName(rs)
+
+		// Try to find symbol under another ABI.
+		var reqABI, haveABI obj.ABI
+		haveABI = ^obj.ABI(0)
+		reqABI, ok := sym.VersionToABI(ldr.SymVersion(rs))
+		if ok {
+			for abi := obj.ABI(0); abi < obj.ABICount; abi++ {
+				v := sym.ABIToVersion(abi)
+				if v == -1 {
+					continue
+				}
+				if rs1 := ldr.Lookup(name, v); rs1 != 0 && ldr.SymType(rs1) != sym.Sxxx && ldr.SymType(rs1) != sym.SXREF {
+					haveABI = abi
+				}
+			}
+		}
+
+		// Give a special error message for main symbol (see #24809).
+		if name == "main.main" {
+			reporter.Errorf(s, "function main is undeclared in the main package")
+		} else if haveABI != ^obj.ABI(0) {
+			reporter.Errorf(s, "relocation target %s not defined for %s (but is defined for %s)", name, reqABI, haveABI)
+		} else {
+			reporter.Errorf(s, "relocation target %s not defined", name)
+		}
+	}
+}