debug/elf: don't apply DWARF relocations for ET_EXEC binaries

Some ET_EXEC binaries might have relocations for non-loadable sections
like .debug_info. These relocations must not be applied, because:
* They may be incorrect
* The correct relocations were already applied at link time

Binaries in Linux Kernel debug packages like Fedora/Centos kernel-debuginfo
are such examples. Relocations for .debug_* sections are included in the
final binaries because they are compiled with --emit-relocs, but the resulting
relocations are incorrect and shouldn't be used when reading DWARF sections.

Fixes #46673

Change-Id: I2b4214f1584bfc243446d0eaee41512657325b95
GitHub-Last-Rev: 8350fad
GitHub-Pull-Request: #46698
Reviewed-on: https://go-review.googlesource.com/c/go/+/327009
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>

src/debug/elf/file.go

@@ -1164,6 +1164,13 @@ func (f *File) DWARF() (*dwarf.Data, error) {
  b = dbuf
  }
 
+ if f.Type == ET_EXEC {
+ // Do not apply relocations to DWARF sections for ET_EXEC binaries.
+ // Relocations should already be applied, and .rela sections may
+ // contain incorrect data.
+ return b, nil
+ }
+
  for _, r := range f.Sections {
  if r.Type != SHT_RELA && r.Type != SHT_REL {
  continue