1 files changed, 87 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 0000000000..e66c518b85
--- /dev/null
+++ b/src/cmd/link/internal/ld/errors.go
@@ -0,0 +1,87 @@
+// 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"
+	"fmt"
+	"os"
+	"sync"
+)
+
+type unresolvedSymKey struct {
+	from *sym.Symbol // Symbol that referenced unresolved "to"
+	to   *sym.Symbol // Unresolved symbol referenced by "from"
+}
+
+type lookupFn func(name string, version int) *sym.Symbol
+type symNameFn func(s loader.Sym) string
+
+// ErrorReporter is used to make error reporting thread safe.
+type ErrorReporter struct {
+	unresOnce  sync.Once
+	unresSyms  map[unresolvedSymKey]bool
+	unresMutex sync.Mutex
+	lookup     lookupFn
+	SymName    symNameFn
+}
+
+// errorUnresolved prints unresolved symbol error for r.Sym that is referenced from s.
+func (reporter *ErrorReporter) errorUnresolved(s *sym.Symbol, r *sym.Reloc) {
+	reporter.unresOnce.Do(func() { reporter.unresSyms = make(map[unresolvedSymKey]bool) })
+
+	k := unresolvedSymKey{from: s, to: r.Sym}
+	reporter.unresMutex.Lock()
+	defer reporter.unresMutex.Unlock()
+	if !reporter.unresSyms[k] {
+		reporter.unresSyms[k] = true
+
+		// Try to find symbol under another ABI.
+		var reqABI, haveABI obj.ABI
+		haveABI = ^obj.ABI(0)
+		reqABI, ok := sym.VersionToABI(int(r.Sym.Version))
+		if ok {
+			for abi := obj.ABI(0); abi < obj.ABICount; abi++ {
+				v := sym.ABIToVersion(abi)
+				if v == -1 {
+					continue
+				}
+				if rs := reporter.lookup(r.Sym.Name, v); rs != nil && rs.Type != sym.Sxxx && rs.Type != sym.SXREF {
+					haveABI = abi
+				}
+			}
+		}
+
+		// Give a special error message for main symbol (see #24809).
+		if r.Sym.Name == "main.main" {
+			Errorf(s, "function main is undeclared in the main package")
+		} else if haveABI != ^obj.ABI(0) {
+			Errorf(s, "relocation target %s not defined for %s (but is defined for %s)", r.Sym.Name, reqABI, haveABI)
+		} else {
+			Errorf(s, "relocation target %s not defined", r.Sym.Name)
+		}
+	}
+}
+
+// Errorf method logs an error message.
+//
+// If more than 20 errors have been printed, exit with an error.
+//
+// Logging an error means that on exit cmd/link will delete any
+// output file and return a non-zero error code.
+// TODO: consolidate the various different versions of Errorf (
+// function, Link method, and ErrorReporter method).
+func (reporter *ErrorReporter) Errorf(s loader.Sym, format string, args ...interface{}) {
+	if s != 0 && reporter.SymName != nil {
+		sn := reporter.SymName(s)
+		format = sn + ": " + format
+	} else {
+		format = fmt.Sprintf("sym %d: %s", s, format)
+	}
+	format += "\n"
+	fmt.Fprintf(os.Stderr, format, args...)
+	afterErrorAction()
+}