cmd/link: fix gdb backtrace on architectures using a link register
Also adds TestGdbBacktrace to the runtime package.
Dwarf modifications written by Bryan Chan (@bryanpkc) who is also
at IBM and covered by the same CLA.
Fixes #14628
Change-Id: I106a1f704c3745a31f29cdadb0032e3905829850
Reviewed-on: https://go-review.googlesource.com/20193
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/src/cmd/link/internal/ld/dwarf.go b/src/cmd/link/internal/ld/dwarf.go
index 0202df6..bf1a7e7 100644
--- a/src/cmd/link/internal/ld/dwarf.go
+++ b/src/cmd/link/internal/ld/dwarf.go
@@ -1619,14 +1619,13 @@
* Emit .debug_frame
*/
const (
- CIERESERVE = 16
- DATAALIGNMENTFACTOR = -4
+ dataAlignmentFactor = -4
)
// appendPCDeltaCFA appends per-PC CFA deltas to b and returns the final slice.
func appendPCDeltaCFA(b []byte, deltapc, cfa int64) []byte {
b = append(b, DW_CFA_def_cfa_offset_sf)
- b = appendSleb128(b, cfa/DATAALIGNMENTFACTOR)
+ b = appendSleb128(b, cfa/dataAlignmentFactor)
switch {
case deltapc < 0x40:
@@ -1654,36 +1653,42 @@
prev.Next = fs
// Emit the CIE, Section 6.4.1
- Adduint32(Ctxt, fs, CIERESERVE) // initial length, must be multiple of thearch.ptrsize
+ cieReserve := uint32(16)
+ if haslinkregister() {
+ cieReserve = 32
+ }
+ Adduint32(Ctxt, fs, cieReserve) // initial length, must be multiple of pointer size
Adduint32(Ctxt, fs, 0xffffffff) // cid.
Adduint8(Ctxt, fs, 3) // dwarf version (appendix F)
Adduint8(Ctxt, fs, 0) // augmentation ""
uleb128put(fs, 1) // code_alignment_factor
- sleb128put(fs, DATAALIGNMENTFACTOR) // guess
+ sleb128put(fs, dataAlignmentFactor) // all CFI offset calculations include multiplication with this factor
uleb128put(fs, int64(Thearch.Dwarfreglr)) // return_address_register
- Adduint8(Ctxt, fs, DW_CFA_def_cfa)
-
- uleb128put(fs, int64(Thearch.Dwarfregsp)) // register SP (**ABI-dependent, defined in l.h)
+ Adduint8(Ctxt, fs, DW_CFA_def_cfa) // Set the current frame address..
+ uleb128put(fs, int64(Thearch.Dwarfregsp)) // ...to use the value in the platform's SP register (defined in l.go)...
if haslinkregister() {
- uleb128put(fs, int64(0)) // offset
- } else {
- uleb128put(fs, int64(SysArch.PtrSize)) // offset
- }
+ uleb128put(fs, int64(0)) // ...plus a 0 offset.
- Adduint8(Ctxt, fs, DW_CFA_offset_extended)
- uleb128put(fs, int64(Thearch.Dwarfreglr)) // return address
- if haslinkregister() {
- uleb128put(fs, int64(0)/DATAALIGNMENTFACTOR) // at cfa - 0
+ Adduint8(Ctxt, fs, DW_CFA_same_value) // The platform's link register is unchanged during the prologue.
+ uleb128put(fs, int64(Thearch.Dwarfreglr))
+
+ Adduint8(Ctxt, fs, DW_CFA_val_offset) // The previous value...
+ uleb128put(fs, int64(Thearch.Dwarfregsp)) // ...of the platform's SP register...
+ uleb128put(fs, int64(0)) // ...is CFA+0.
} else {
- uleb128put(fs, int64(-SysArch.PtrSize)/DATAALIGNMENTFACTOR) // at cfa - x*4
+ uleb128put(fs, int64(SysArch.PtrSize)) // ...plus the word size (because the call instruction implicitly adds one word to the frame).
+
+ Adduint8(Ctxt, fs, DW_CFA_offset_extended) // The previous value...
+ uleb128put(fs, int64(Thearch.Dwarfreglr)) // ...of the return address...
+ uleb128put(fs, int64(-SysArch.PtrSize)/dataAlignmentFactor) // ...is saved at [CFA - (PtrSize/4)].
}
// 4 is to exclude the length field.
- pad := CIERESERVE + 4 - fs.Size
+ pad := int64(cieReserve) + 4 - fs.Size
if pad < 0 {
- Exitf("dwarf: CIERESERVE too small by %d bytes.", -pad)
+ Exitf("dwarf: cieReserve too small by %d bytes.", -pad)
}
Addbytes(Ctxt, fs, zeros[:pad])
@@ -1712,6 +1717,21 @@
}
if haslinkregister() {
+ // TODO(bryanpkc): This is imprecise. In general, the instruction
+ // that stores the return address to the stack frame is not the
+ // same one that allocates the frame.
+ if pcsp.value > 0 {
+ // The return address is preserved at (CFA-frame_size)
+ // after a stack frame has been allocated.
+ deltaBuf = append(deltaBuf, DW_CFA_offset_extended_sf)
+ deltaBuf = appendUleb128(deltaBuf, uint64(Thearch.Dwarfreglr))
+ deltaBuf = appendSleb128(deltaBuf, -int64(pcsp.value)/dataAlignmentFactor)
+ } else {
+ // The return address is restored into the link register
+ // when a stack frame has been de-allocated.
+ deltaBuf = append(deltaBuf, DW_CFA_same_value)
+ deltaBuf = appendUleb128(deltaBuf, uint64(Thearch.Dwarfreglr))
+ }
deltaBuf = appendPCDeltaCFA(deltaBuf, int64(nextpc)-int64(pcsp.pc), int64(pcsp.value))
} else {
deltaBuf = appendPCDeltaCFA(deltaBuf, int64(nextpc)-int64(pcsp.pc), int64(SysArch.PtrSize)+int64(pcsp.value))
diff --git a/src/runtime/runtime-gdb_test.go b/src/runtime/runtime-gdb_test.go
index 7cfcefc..4f82646 100644
--- a/src/runtime/runtime-gdb_test.go
+++ b/src/runtime/runtime-gdb_test.go
@@ -3,6 +3,7 @@
import (
"bytes"
"fmt"
+ "internal/testenv"
"io/ioutil"
"os"
"os/exec"
@@ -13,19 +14,22 @@
"testing"
)
-func checkGdbPython(t *testing.T) {
- cmd := exec.Command("gdb", "-nx", "-q", "--batch", "-iex", "python import sys; print('go gdb python support')")
- out, err := cmd.CombinedOutput()
-
- if err != nil {
- t.Skipf("skipping due to issue running gdb: %v", err)
+func checkGdbEnvironment(t *testing.T) {
+ testenv.MustHaveGoBuild(t)
+ if runtime.GOOS == "darwin" {
+ t.Skip("gdb does not work on darwin")
}
- if string(out) != "go gdb python support\n" {
- t.Skipf("skipping due to lack of python gdb support: %s", out)
+ if final := os.Getenv("GOROOT_FINAL"); final != "" && runtime.GOROOT() != final {
+ t.Skip("gdb test can fail with GOROOT_FINAL pending")
}
+}
+func checkGdbVersion(t *testing.T) {
// Issue 11214 reports various failures with older versions of gdb.
- out, err = exec.Command("gdb", "--version").CombinedOutput()
+ out, err := exec.Command("gdb", "--version").CombinedOutput()
+ if err != nil {
+ t.Skipf("skipping: error executing gdb: %v", err)
+ }
re := regexp.MustCompile(`([0-9]+)\.([0-9]+)`)
matches := re.FindSubmatch(out)
if len(matches) < 3 {
@@ -42,6 +46,18 @@
t.Logf("gdb version %d.%d", major, minor)
}
+func checkGdbPython(t *testing.T) {
+ cmd := exec.Command("gdb", "-nx", "-q", "--batch", "-iex", "python import sys; print('go gdb python support')")
+ out, err := cmd.CombinedOutput()
+
+ if err != nil {
+ t.Skipf("skipping due to issue running gdb: %v", err)
+ }
+ if string(out) != "go gdb python support\n" {
+ t.Skipf("skipping due to lack of python gdb support: %s", out)
+ }
+}
+
const helloSource = `
package main
import "fmt"
@@ -57,13 +73,8 @@
`
func TestGdbPython(t *testing.T) {
- if runtime.GOOS == "darwin" {
- t.Skip("gdb does not work on darwin")
- }
- if final := os.Getenv("GOROOT_FINAL"); final != "" && runtime.GOROOT() != final {
- t.Skip("gdb test can fail with GOROOT_FINAL pending")
- }
-
+ checkGdbEnvironment(t)
+ checkGdbVersion(t)
checkGdbPython(t)
dir, err := ioutil.TempDir("", "go-build")
@@ -162,3 +173,82 @@
t.Logf("gdb cannot backtrace for GOARCH=%s, skipped goroutine backtrace test", runtime.GOARCH)
}
}
+
+const backtraceSource = `
+package main
+
+//go:noinline
+func aaa() bool { return bbb() }
+
+//go:noinline
+func bbb() bool { return ccc() }
+
+//go:noinline
+func ccc() bool { return ddd() }
+
+//go:noinline
+func ddd() bool { return f() }
+
+//go:noinline
+func eee() bool { return true }
+
+var f = eee
+
+func main() {
+ _ = aaa()
+}
+`
+
+// TestGdbBacktrace tests that gdb can unwind the stack correctly
+// using only the DWARF debug info.
+func TestGdbBacktrace(t *testing.T) {
+ checkGdbEnvironment(t)
+ checkGdbVersion(t)
+
+ dir, err := ioutil.TempDir("", "go-build")
+ if err != nil {
+ t.Fatalf("failed to create temp directory: %v", err)
+ }
+ defer os.RemoveAll(dir)
+
+ // Build the source code.
+ src := filepath.Join(dir, "main.go")
+ err = ioutil.WriteFile(src, []byte(backtraceSource), 0644)
+ if err != nil {
+ t.Fatalf("failed to create file: %v", err)
+ }
+ cmd := exec.Command("go", "build", "-o", "a.exe")
+ cmd.Dir = dir
+ out, err := testEnv(cmd).CombinedOutput()
+ if err != nil {
+ t.Fatalf("building source %v\n%s", err, out)
+ }
+
+ // Execute gdb commands.
+ args := []string{"-nx", "-batch",
+ "-ex", "break main.eee",
+ "-ex", "run",
+ "-ex", "backtrace",
+ "-ex", "continue",
+ filepath.Join(dir, "a.exe"),
+ }
+ got, _ := exec.Command("gdb", args...).CombinedOutput()
+
+ // Check that the backtrace matches the source code.
+ bt := []string{
+ "eee",
+ "ddd",
+ "ccc",
+ "bbb",
+ "aaa",
+ "main",
+ }
+ for i, name := range bt {
+ s := fmt.Sprintf("#%v.*main\\.%v", i, name)
+ re := regexp.MustCompile(s)
+ if found := re.Find(got) != nil; !found {
+ t.Errorf("could not find '%v' in backtrace", s)
+ t.Fatalf("gdb output:\n%v", string(got))
+ }
+ }
+}
