Would be nice to have a raw dump of .debug_line similar to readelf --debug-dump=rawline

[llvmbot]

Bugzilla Link	18840
Version	trunk
OS	Linux
Reporter	LLVM Bugzilla Contributor
CC	@dbaron,@dnovillo,@echristo,@MaskRay,@jh7370,@nickdesaulniers

Extended Description

llvm-darfdump can dump debug lines, but it does that for each compile unit and therefore needs to parse .debug_info.

For testing, it would be nice to have something simpler, like "readelf --debug-dump=rawline" or what we currently have in "llvm-readobj
-codeview-linetables". It should probably go in llvm-readobj somewhere.

[nickdesaulniers]

Additionally, not having support for --debug-dump=* in llvm-readelf makes use of llvm-readelf as a drop in replacement for GNU readelf more difficult.

It was suggested on LKML to use that for detecting DWARF version actually used. I recognize that llvm-dwarfdump fills a similar role; it's the difference in command line argument support that makes substituting one for the other more difficult.

[MaskRay]

objcopy -R .debug_info a.o b.o
llvm-dwarfdump -debug-line b.o => output

So llvm-dwarfdump can actually dump .debug_line without .debug_info

As of whether readelf --debug-dump=rawline is useful, I am not sure. I am not sure adding the readelf style strings are useful given that we have llvm-dwarfdump -debug-line -v

[0x00000025] Extended opcode 2: set Address to 0x0
[0x00000030] Advance Line by 10 to 11
[0x00000032] Copy
[0x00000033] Set column to 3
[0x00000035] Set prologue_end to true
[0x00000036] Special opcode 62: advance Address by 4 to 0x4 and Line by 1 to 12
[0x00000037] Advance PC by 7 to 0xb
[0x00000039] Extended opcode 1: End of Sequence

To obtain the version of a .debug_info, parse , version = 0x0004, from llvm-dwarfdump -debug-info output
To obtain the version of a .debug_line, parse version: 4 from -debug-line output.

Another way to extract the version field is to dump the first 6 or 14 bytes.
The section header is usually: unit_length (4 or 12 bytes) + version (uhalf)