diff --git a/src/cmd/gofmt/gofmt.go b/src/cmd/gofmt/gofmt.go
index bbb8b4fd15c2f7..ad6ad636524479 100644
--- a/src/cmd/gofmt/gofmt.go
+++ b/src/cmd/gofmt/gofmt.go
@@ -41,6 +41,9 @@ var (
 
 	// debugging
 	cpuprofile = flag.String("cpuprofile", "", "write cpu profile to this file")
+
+	// errors
+	errFormattingDiffers = fmt.Errorf("formatting differs from gofmt's")
 )
 
 // Keep these in sync with go/format/format.go.
@@ -218,8 +221,12 @@ func (r *reporter) Report(err error) {
 		panic("Report with nil error")
 	}
 	st := r.getState()
-	scanner.PrintError(st.err, err)
-	st.exitCode = 2
+	if err == errFormattingDiffers {
+		st.exitCode = 1
+	} else {
+		scanner.PrintError(st.err, err)
+		st.exitCode = 2
+	}
 }
 
 func (r *reporter) ExitCode() int {
@@ -281,6 +288,7 @@ func processFile(filename string, info fs.FileInfo, in io.Reader, r *reporter) e
 			newName := filepath.ToSlash(filename)
 			oldName := newName + ".orig"
 			r.Write(diff.Diff(oldName, src, newName, res))
+			return errFormattingDiffers
 		}
 	}
 
diff --git a/src/cmd/gofmt/gofmt_test.go b/src/cmd/gofmt/gofmt_test.go
index 6b80673af148f5..2aba0f03ff09e9 100644
--- a/src/cmd/gofmt/gofmt_test.go
+++ b/src/cmd/gofmt/gofmt_test.go
@@ -53,10 +53,19 @@ func gofmtFlags(filename string, maxLines int) string {
 	return ""
 }
 
-func runTest(t *testing.T, in, out string) {
-	// process flags
-	*simplifyAST = false
+// Reset global variables for all flags to their default value.
+func resetFlags() {
+	*list = false
+	*write = false
 	*rewriteRule = ""
+	*simplifyAST = false
+	*doDiff = false
+	*allErrors = false
+	*cpuprofile = ""
+}
+
+func runTest(t *testing.T, in, out string) {
+	resetFlags()
 	info, err := os.Lstat(in)
 	if err != nil {
 		t.Error(err)
@@ -159,6 +168,46 @@ func TestRewrite(t *testing.T) {
 	}
 }
 
+// TestDiff runs gofmt with the -d flag on the input files and checks that the
+// expected exit code is set.
+func TestDiff(t *testing.T) {
+	tests := []struct {
+		in       string
+		exitCode int
+	}{
+		{in: "testdata/exitcode.input", exitCode: 1},
+		{in: "testdata/exitcode.golden", exitCode: 0},
+	}
+
+	for _, tt := range tests {
+		resetFlags()
+		*doDiff = true
+
+		initParserMode()
+		initRewrite()
+
+		info, err := os.Lstat(tt.in)
+		if err != nil {
+			t.Error(err)
+			return
+		}
+
+		const maxWeight = 2 << 20
+		var buf, errBuf bytes.Buffer
+		s := newSequencer(maxWeight, &buf, &errBuf)
+		s.Add(fileWeight(tt.in, info), func(r *reporter) error {
+			return processFile(tt.in, info, nil, r)
+		})
+		if errBuf.Len() > 0 {
+			t.Logf("%q", errBuf.Bytes())
+		}
+
+		if s.GetExitCode() != tt.exitCode {
+			t.Errorf("%s: expected exit code %d, got %d", tt.in, tt.exitCode, s.GetExitCode())
+		}
+	}
+}
+
 // Test case for issue 3961.
 func TestCRLF(t *testing.T) {
 	const input = "testdata/crlf.input"   // must contain CR/LF's
diff --git a/src/cmd/gofmt/testdata/exitcode.golden b/src/cmd/gofmt/testdata/exitcode.golden
new file mode 100644
index 00000000000000..06ab7d0f9a35a7
--- /dev/null
+++ b/src/cmd/gofmt/testdata/exitcode.golden
@@ -0,0 +1 @@
+package main
diff --git a/src/cmd/gofmt/testdata/exitcode.input b/src/cmd/gofmt/testdata/exitcode.input
new file mode 100644
index 00000000000000..4f2f092ce508de
--- /dev/null
+++ b/src/cmd/gofmt/testdata/exitcode.input
@@ -0,0 +1 @@
+	package main
diff --git a/src/debug/elf/file.go b/src/debug/elf/file.go
index 50452b5bef45f4..1d56a06c3fb221 100644
--- a/src/debug/elf/file.go
+++ b/src/debug/elf/file.go
@@ -25,6 +25,7 @@ import (
 	"internal/saferio"
 	"internal/zstd"
 	"io"
+	"math"
 	"os"
 	"strings"
 	"unsafe"
@@ -830,17 +831,9 @@ func (f *File) applyRelocationsAMD64(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_X86_64_64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
 		case R_X86_64_32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -872,12 +865,7 @@ func (f *File) applyRelocations386(dst []byte, rels []byte) error {
 		sym := &symbols[symNo-1]
 
 		if t == R_386_32 {
-			if rel.Off+4 >= uint32(len(dst)) {
-				continue
-			}
-			val := f.ByteOrder.Uint32(dst[rel.Off : rel.Off+4])
-			val += uint32(sym.Value)
-			f.ByteOrder.PutUint32(dst[rel.Off:rel.Off+4], val)
+			putUint(f.ByteOrder, dst, uint64(rel.Off), 4, sym.Value, 0, true)
 		}
 	}
 
@@ -910,12 +898,7 @@ func (f *File) applyRelocationsARM(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_ARM_ABS32:
-			if rel.Off+4 >= uint32(len(dst)) {
-				continue
-			}
-			val := f.ByteOrder.Uint32(dst[rel.Off : rel.Off+4])
-			val += uint32(sym.Value)
-			f.ByteOrder.PutUint32(dst[rel.Off:rel.Off+4], val)
+			putUint(f.ByteOrder, dst, uint64(rel.Off), 4, sym.Value, 0, true)
 		}
 	}
 
@@ -955,17 +938,9 @@ func (f *File) applyRelocationsARM64(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_AARCH64_ABS64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
 		case R_AARCH64_ABS32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -1001,11 +976,7 @@ func (f *File) applyRelocationsPPC(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_PPC_ADDR32:
-			if rela.Off+4 >= uint32(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, uint64(rela.Off), 4, sym.Value, 0, false)
 		}
 	}
 
@@ -1041,17 +1012,9 @@ func (f *File) applyRelocationsPPC64(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_PPC64_ADDR64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
 		case R_PPC64_ADDR32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -1084,12 +1047,7 @@ func (f *File) applyRelocationsMIPS(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_MIPS_32:
-			if rel.Off+4 >= uint32(len(dst)) {
-				continue
-			}
-			val := f.ByteOrder.Uint32(dst[rel.Off : rel.Off+4])
-			val += uint32(sym.Value)
-			f.ByteOrder.PutUint32(dst[rel.Off:rel.Off+4], val)
+			putUint(f.ByteOrder, dst, uint64(rel.Off), 4, sym.Value, 0, true)
 		}
 	}
 
@@ -1132,17 +1090,9 @@ func (f *File) applyRelocationsMIPS64(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_MIPS_64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
 		case R_MIPS_32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -1180,17 +1130,9 @@ func (f *File) applyRelocationsLOONG64(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_LARCH_64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
 		case R_LARCH_32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -1226,17 +1168,9 @@ func (f *File) applyRelocationsRISCV64(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_RISCV_64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
 		case R_RISCV_32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -1272,17 +1206,9 @@ func (f *File) applyRelocationss390x(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_390_64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
 		case R_390_32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -1318,17 +1244,10 @@ func (f *File) applyRelocationsSPARC64(dst []byte, rels []byte) error {
 
 		switch t {
 		case R_SPARC_64, R_SPARC_UA64:
-			if rela.Off+8 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val64 := sym.Value + uint64(rela.Addend)
-			f.ByteOrder.PutUint64(dst[rela.Off:rela.Off+8], val64)
+			putUint(f.ByteOrder, dst, rela.Off, 8, sym.Value, rela.Addend, false)
+
 		case R_SPARC_32, R_SPARC_UA32:
-			if rela.Off+4 >= uint64(len(dst)) || rela.Addend < 0 {
-				continue
-			}
-			val32 := uint32(sym.Value) + uint32(rela.Addend)
-			f.ByteOrder.PutUint32(dst[rela.Off:rela.Off+4], val32)
+			putUint(f.ByteOrder, dst, rela.Off, 4, sym.Value, rela.Addend, false)
 		}
 	}
 
@@ -1903,3 +1822,38 @@ type nobitsSectionReader struct{}
 func (*nobitsSectionReader) ReadAt(p []byte, off int64) (n int, err error) {
 	return 0, errors.New("unexpected read from SHT_NOBITS section")
 }
+
+// putUint writes a relocation to slice
+// at offset start of length length (4 or 8 bytes),
+// adding sym+addend to the existing value if readUint is true,
+// or just writing sym+addend if readUint is false.
+// If the write would extend beyond the end of slice, putUint does nothing.
+// If the addend is negative, putUint does nothing.
+// If the addition would overflow, putUint does nothing.
+func putUint(byteOrder binary.ByteOrder, slice []byte, start, length, sym uint64, addend int64, readUint bool) {
+	if start+length > uint64(len(slice)) || math.MaxUint64-start < length {
+		return
+	}
+	if addend < 0 {
+		return
+	}
+
+	s := slice[start : start+length]
+
+	switch length {
+	case 4:
+		ae := uint32(addend)
+		if readUint {
+			ae += byteOrder.Uint32(s)
+		}
+		byteOrder.PutUint32(s, uint32(sym)+ae)
+	case 8:
+		ae := uint64(addend)
+		if readUint {
+			ae += byteOrder.Uint64(s)
+		}
+		byteOrder.PutUint64(s, sym+ae)
+	default:
+		panic("can't happen")
+	}
+}