[DWARF] Dump .gdb_index of version 8

[MaskRay]

Summary

gdb index version was bumped from 7 to 8 by commit 796a7ff8234cfaa8ad1ab884c1c8dafe29b18d42.
The format doesn't change.

Accept version 8 so that we can dump .gdb_index built by the 'save gdb-index' command of gdb (Jan 2013 or newer). Manually verified the result is plausible:

mkdir dir; gdb a -batch -q -ex 'save gdb-index dir'; objcopy --add-section .gdb_index=dir/a.gdb-index --set-section-flags .gdb_index=readonly a b
llvm-dwarfdump -gdb-index b

[grimar]

Do you know why the version was changed but the format remained the same?

[MaskRay]

In D64396#1575515, @grimar wrote:

Do you know why the version was changed but the format remained the same?

I think it was just to work around https://sourceware.org/bugzilla/show_bug.cgi?id=15021

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=796a7ff8234cfaa8ad1ab884c1c8dafe29b18d42

Also see my comment at https://reviews.llvm.org/D63537#1575513

[grimar]

Well, since this allows dumping the "newer" format, it looks like a step forward, so I have no objections.

test/DebugInfo/dwarfdump-dump-gdbindex.test

7

Side note: seems we might want to try to improve yaml2obj to support the .gdb_index.

[ikudrin]

test/DebugInfo/dwarfdump-dump-gdbindex.test

6

Personally, I'd prefer to have another binary file for version 8 than patching the existing one. What do you think?

[MaskRay]

test/DebugInfo/dwarfdump-dump-gdbindex.test

6

I think that is not very necessary at the moment. We can do that after the non-empty types CU list issue is fixed or when yaml2obj gets improved to handle .gdb_index

lib/DebugInfo/DWARF/DWARFGdbIndex.cpp

if (HasContent) {
     dumpSymbolTable(OS);
     dumpConstantPool(OS);
   }
 }
 
 bool DWARFGdbIndex::parseImpl(DataExtractor Data) {
   uint32_t Offset = 0;
 
-  // Only version 7 is supported at this moment.
+  // Only versions 7 and 8 are supported at this moment.
   Version = Data.getU32(&Offset);
-  if (Version != 7)
+  if (Version != 7 && Version != 8)
     return false;
 
   CuListOffset = Data.getU32(&Offset);
   TuListOffset = Data.getU32(&Offset);
   AddressAreaOffset = Data.getU32(&Offset);
   SymbolTableOffset = Data.getU32(&Offset);
   ConstantPoolOffset = Data.getU32(&Offset);
 

test/DebugInfo/dwarfdump-dump-gdbindex.test

-RUN: llvm-dwarfdump -gdb-index %p/Inputs/dwarfdump-gdbindex-v7.elf-x86-64 | FileCheck %s
+RUN: llvm-dwarfdump -gdb-index %p/Inputs/dwarfdump-gdbindex-v7.elf-x86-64 | \
+RUN:   FileCheck --check-prefixes=CHECK,CHECK-V7 %s
+
+; Change the version number (first byte of .gdb_index) from 7 to 8.
+RUN: cp %p/Inputs/dwarfdump-gdbindex-v7.elf-x86-64 %t
+RUN: %python -c 'with open("%/t", "r+b") as f: f.seek(0x1748); f.write(b"\x08")'
+RUN: llvm-dwarfdump -gdb-index %t | FileCheck --check-prefixes=CHECK,CHECK-V8 %s
 
 ; test.cpp:
 ; int main() { return 0; }
 ; test2.cpp:
 ; int main2() { return 0; }
 ; Compiled with:
 ; gcc -gsplit-dwarf -c test.cpp test2.cpp
 ; gold --gdb-index test.o test2.o -o dwarfdump-gdbindex-v7.elf-x86-64
 ; gcc version 5.3.1 20160413, GNU gold (GNU Binutils for Ubuntu 2.26) 1.11
 ; Info about gdb-index: https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html
 
 ; CHECK-LABEL: .gdb_index contents:
-; CHECK: Version = 7
+; CHECK-V7: Version = 7
+; CHECK-V8: Version = 8
 
 ; CHECK:      CU list offset = 0x18, has 2 entries:
 ; CHECK-NEXT:   0: Offset = 0x0, Length = 0x34
 ; CHECK-NEXT:   1: Offset = 0x34, Length = 0x34
 
 ; CHECK:      Types CU list offset = 0x38, has 0 entries:
 
 ; CHECK:      Address area offset = 0x38, has 2 entries: