debug/dwarf: fix problem with DWARF 5 and Seek method
When clients use debug/dwarf to examine DWARF 5 binaries, we can run
into problems when the Seek() method is used to skip ahead from a DIE
in one compilation unit to a DIE in another unit. The problem here is
that it is common for DWARF 5 comp units to have attributes (ex:
DW_AT_addr_base) whose value must be applied as an offset when reading
certain forms (ex: DW_FORM_addrx) within that unit. The existing
implementation didn't have a good way to recover these attrs following
the Seek call, and had to essentially punt in this case, resulting in
incorrect attr values.
This patch adds new support for reading and caching the key comp unit
DIE attributes (DW_AT_addr_base, DW_AT_loclists_base, etc) prior to
visiting any of the DIE entries in a unit, storing the cache values of
these attrs the main table of units. This base attribute
reading/caching behavior also happens (where needed) after Seek calls.
Should resolve delve issue 3861.
Supercedes Go pull request 70400.
Updates #26379.
Fixes #57046.
Change-Id: I536a57e2ba4fc55132d91c7f36f67a91ac408dc3
Reviewed-on: https://go-review.googlesource.com/c/go/+/655976
Reviewed-by: Alessandro Arzilli <alessandro.arzilli@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
diff --git a/src/debug/dwarf/entry.go b/src/debug/dwarf/entry.go
index 3e54a1a..ed0f213 100644
--- a/src/debug/dwarf/entry.go
+++ b/src/debug/dwarf/entry.go
@@ -426,16 +426,6 @@
Field: make([]Field, len(a.field)),
}
- // If we are currently parsing the compilation unit,
- // we can't evaluate Addrx or Strx until we've seen the
- // relevant base entry.
- type delayed struct {
- idx int
- off uint64
- fmt format
- }
- var delay []delayed
-
resolveStrx := func(strBase, off uint64) string {
off += strBase
if uint64(int(off)) != off {
@@ -532,18 +522,7 @@
return nil
}
- // We have to adjust by the offset of the
- // compilation unit. This won't work if the
- // program uses Reader.Seek to skip over the
- // unit. Not much we can do about that.
- var addrBase int64
- if cu != nil {
- addrBase, _ = cu.Val(AttrAddrBase).(int64)
- } else if a.tag == TagCompileUnit {
- delay = append(delay, delayed{i, off, formAddrx})
- break
- }
-
+ addrBase := int64(u.addrBase())
var err error
val, err = b.dwarf.debugAddr(b.format, uint64(addrBase), off)
if err != nil {
@@ -683,18 +662,7 @@
off *= 4
}
- // We have to adjust by the offset of the
- // compilation unit. This won't work if the
- // program uses Reader.Seek to skip over the
- // unit. Not much we can do about that.
- var strBase int64
- if cu != nil {
- strBase, _ = cu.Val(AttrStrOffsetsBase).(int64)
- } else if a.tag == TagCompileUnit {
- delay = append(delay, delayed{i, off, formStrx})
- break
- }
-
+ strBase := int64(u.strOffsetsBase())
val = resolveStrx(uint64(strBase), off)
case formStrpSup:
@@ -743,18 +711,7 @@
case formRnglistx:
off := b.uint()
- // We have to adjust by the rnglists_base of
- // the compilation unit. This won't work if
- // the program uses Reader.Seek to skip over
- // the unit. Not much we can do about that.
- var rnglistsBase int64
- if cu != nil {
- rnglistsBase, _ = cu.Val(AttrRnglistsBase).(int64)
- } else if a.tag == TagCompileUnit {
- delay = append(delay, delayed{i, off, formRnglistx})
- break
- }
-
+ rnglistsBase := int64(u.rngListsBase())
val = resolveRnglistx(uint64(rnglistsBase), off)
}
@@ -763,32 +720,6 @@
if b.err != nil {
return nil
}
-
- for _, del := range delay {
- switch del.fmt {
- case formAddrx:
- addrBase, _ := e.Val(AttrAddrBase).(int64)
- val, err := b.dwarf.debugAddr(b.format, uint64(addrBase), del.off)
- if err != nil {
- b.err = err
- return nil
- }
- e.Field[del.idx].Val = val
- case formStrx:
- strBase, _ := e.Val(AttrStrOffsetsBase).(int64)
- e.Field[del.idx].Val = resolveStrx(uint64(strBase), del.off)
- if b.err != nil {
- return nil
- }
- case formRnglistx:
- rnglistsBase, _ := e.Val(AttrRnglistsBase).(int64)
- e.Field[del.idx].Val = resolveRnglistx(uint64(rnglistsBase), del.off)
- if b.err != nil {
- return nil
- }
- }
- }
-
return e
}
@@ -840,6 +771,7 @@
u := &d.unit[0]
r.unit = 0
r.b = makeBuf(r.d, u, "info", u.off, u.data)
+ r.collectDwarf5BaseOffsets(u)
r.cu = nil
return
}
@@ -855,6 +787,7 @@
u := &d.unit[i]
r.unit = i
r.b = makeBuf(r.d, u, "info", off, u.data[off-u.off:])
+ r.collectDwarf5BaseOffsets(u)
}
// maybeNextUnit advances to the next unit if this one is finished.
@@ -870,6 +803,17 @@
u := &r.d.unit[r.unit]
r.b = makeBuf(r.d, u, "info", u.off, u.data)
r.cu = nil
+ r.collectDwarf5BaseOffsets(u)
+}
+
+func (r *Reader) collectDwarf5BaseOffsets(u *unit) {
+ if u.vers < 5 || u.unit5 != nil {
+ return
+ }
+ u.unit5 = new(unit5)
+ if err := r.d.collectDwarf5BaseOffsets(u); err != nil {
+ r.err = err
+ }
}
// Next reads the next entry from the encoded entry stream.
diff --git a/src/debug/dwarf/entry_test.go b/src/debug/dwarf/entry_test.go
index 1ce1c98..ee0c80a 100644
--- a/src/debug/dwarf/entry_test.go
+++ b/src/debug/dwarf/entry_test.go
@@ -6,6 +6,7 @@
import (
. "debug/dwarf"
+ "debug/elf"
"encoding/binary"
"path/filepath"
"reflect"
@@ -457,3 +458,62 @@
t.Errorf("got non-nil entry0, wanted nil")
}
}
+
+func TestIssue57046(t *testing.T) {
+ f, err := elf.Open("testdata/issue57046-clang.elf5")
+ if err != nil {
+ t.Fatalf("elf.Open returns err: %v", err)
+ }
+ d, err := f.DWARF()
+ if err != nil {
+ t.Fatalf("f.DWARF returns err: %v", err)
+ }
+ // Write down all the subprogram DIEs.
+ spdies := []Offset{}
+ lopcs := []uint64{}
+ r := d.Reader()
+ for {
+ e, err := r.Next()
+ if err != nil {
+ t.Fatalf("r.Next() returns err: %v", err)
+ }
+ if e == nil {
+ break
+ }
+ if e.Tag != TagSubprogram {
+ continue
+ }
+ var name string
+ var lopc uint64
+ if n, ok := e.Val(AttrName).(string); ok {
+ name = n
+ }
+ if lo, ok := e.Val(AttrLowpc).(uint64); ok {
+ lopc = lo
+ }
+ if name == "" || lopc == 0 {
+ continue
+ }
+ spdies = append(spdies, e.Offset)
+ lopcs = append(lopcs, lopc)
+ }
+
+ // Seek to the second entry in spdies (corresponding to mom() in
+ // issue57046_part2.c) and take a look at it.
+ r2 := d.Reader()
+ r2.Seek(spdies[1])
+ e, err := r2.Next()
+ if err != nil {
+ t.Fatalf("r2.Next() returns err: %v", err)
+ }
+ if e == nil {
+ t.Fatalf("r2.Next() returned nil")
+ }
+
+ // Verify that the lopc we see matches what we saw before.
+ got := e.Val(AttrLowpc).(uint64)
+ if got != lopcs[1] {
+ t.Errorf("bad lopc for fn2 following seek: want %x got %x\n",
+ lopcs[1], got)
+ }
+}
diff --git a/src/debug/dwarf/testdata/issue57046-clang.elf5 b/src/debug/dwarf/testdata/issue57046-clang.elf5
new file mode 100755
index 0000000..009af83
--- /dev/null
+++ b/src/debug/dwarf/testdata/issue57046-clang.elf5
Binary files differ
diff --git a/src/debug/dwarf/testdata/issue57046_part1.c b/src/debug/dwarf/testdata/issue57046_part1.c
new file mode 100644
index 0000000..8866ca6
--- /dev/null
+++ b/src/debug/dwarf/testdata/issue57046_part1.c
@@ -0,0 +1,42 @@
+// 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.
+
+// Part 1 of the sources for issue 57046 test case.
+
+// Build instructions:
+//
+// clang-16 -O -g -gdwarf-5 -c issue57046_part1.c
+// clang-16 -O -g -gdwarf-5 -c issue57046_part2.c
+// clang-16 -o issue57046-clang.elf5 issue57046_part1.o issue57046_part2.o
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+extern const char *mom();
+
+int gadgety() {
+ const char *ev = getenv("PATH");
+ int n = strlen(ev);
+ int s1 = (int)ev[0];
+ int s2 = (int)ev[1];
+ int s3 = (int)ev[2];
+ for (int i = 0; i < strlen(ev); i++) {
+ if (s1 == 101) {
+ int t = s1;
+ s1 = s3;
+ s3 = t;
+ }
+ if (ev[i] == 99) {
+ printf("%d\n", i);
+ }
+ }
+ s2 *= 2;
+ return n + s1 + s2;
+}
+
+int main(int argc, char **argv) {
+ printf("Hi %s %d\n", mom(), gadgety());
+ return 0;
+}
diff --git a/src/debug/dwarf/testdata/issue57046_part2.c b/src/debug/dwarf/testdata/issue57046_part2.c
new file mode 100644
index 0000000..2f4e9f0
--- /dev/null
+++ b/src/debug/dwarf/testdata/issue57046_part2.c
@@ -0,0 +1,10 @@
+// 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.
+
+// Part 2 of the sources for issue 57046 test case.
+// See part 1 for build instructions.
+
+const char *mom() {
+ return "mom";
+}
diff --git a/src/debug/dwarf/unit.go b/src/debug/dwarf/unit.go
index 8b810d0..7a384f3 100644
--- a/src/debug/dwarf/unit.go
+++ b/src/debug/dwarf/unit.go
@@ -17,10 +17,18 @@
off Offset // byte offset of data within the aggregate info
data []byte
atable abbrevTable
+ *unit5 // info specific to DWARF 5 units
asize int
vers int
- utype uint8 // DWARF 5 unit type
is64 bool // True for 64-bit DWARF format
+ utype uint8 // DWARF 5 unit type
+}
+
+type unit5 struct {
+ addrBase uint64
+ strOffsetsBase uint64
+ rngListsBase uint64
+ locListsBase uint64
}
// Implement the dataFormat interface.
@@ -37,6 +45,34 @@
return u.asize
}
+func (u *unit) addrBase() uint64 {
+ if u.unit5 != nil {
+ return u.unit5.addrBase
+ }
+ return 0
+}
+
+func (u *unit) strOffsetsBase() uint64 {
+ if u.unit5 != nil {
+ return u.unit5.strOffsetsBase
+ }
+ return 0
+}
+
+func (u *unit) rngListsBase() uint64 {
+ if u.unit5 != nil {
+ return u.unit5.rngListsBase
+ }
+ return 0
+}
+
+func (u *unit) locListsBase() uint64 {
+ if u.unit5 != nil {
+ return u.unit5.locListsBase
+ }
+ return 0
+}
+
func (d *Data) parseUnits() ([]unit, error) {
// Count units.
nunit := 0
@@ -135,3 +171,30 @@
}
return -1
}
+
+func (d *Data) collectDwarf5BaseOffsets(u *unit) error {
+ if u.unit5 == nil {
+ panic("expected unit5 to be set up already")
+ }
+ b := makeBuf(d, u, "info", u.off, u.data)
+ cu := b.entry(nil, u)
+ if cu == nil {
+ // Unknown abbreviation table entry or some other fatal
+ // problem; bail early on the assumption that this will be
+ // detected at some later point.
+ return b.err
+ }
+ if iAddrBase, ok := cu.Val(AttrAddrBase).(int64); ok {
+ u.unit5.addrBase = uint64(iAddrBase)
+ }
+ if iStrOffsetsBase, ok := cu.Val(AttrStrOffsetsBase).(int64); ok {
+ u.unit5.strOffsetsBase = uint64(iStrOffsetsBase)
+ }
+ if iRngListsBase, ok := cu.Val(AttrRnglistsBase).(int64); ok {
+ u.unit5.rngListsBase = uint64(iRngListsBase)
+ }
+ if iLocListsBase, ok := cu.Val(AttrLoclistsBase).(int64); ok {
+ u.unit5.locListsBase = uint64(iLocListsBase)
+ }
+ return nil
+}
