Use DWARF debug format option

[chrisbodhi]

Addresses #19478

[chrisbodhi]

This works as expected with

$ zig build-obj -gdwarf32 -O Debug -target x86_64-linux example.zig

$ /opt/homebrew/opt/binutils/bin/objdump --dwarf=info example.o | head -20

example.o:     file format elf64-x86-64

Contents of the .debug_info section:

  Compilation Unit @ offset 0:
   Length:        0x25f5a (32-bit)
   Version:       4
   Abbrev Offset: 0
   Pointer Size:  8
...

and

$ zig build-obj -gdwarf64 -O Debug -target x86_64-linux example.zig

$ /opt/homebrew/opt/binutils/bin/objdump --dwarf=info example.o | head -20

example.o:     file format elf64-x86-64

Contents of the .debug_info section:

  Compilation Unit @ offset 0:
   Length:        0x31232 (64-bit)
   Version:       4
   Abbrev Offset: 0
   Pointer Size:  8
...

But, reviewing my code, I'm unsure of what the behavior would be if debug_format were empty. I can see that a 32-bit size is used when no flag is added:

$ zig build-obj -O Debug -target x86_64-linux example.zig

$ /opt/homebrew/opt/binutils/bin/objdump --dwarf=info example.o | head -20

example.o:     file format elf64-x86-64

Contents of the .debug_info section:

  Compilation Unit @ offset 0:
   Length:        0x25f5a (32-bit)
   Version:       4
   Abbrev Offset: 0
   Pointer Size:  8
...

Is this wanted?

[geezmolycos]

I can see in past versions 32-bit format was used, and the -dwarf64 option was added to resolve a specific problem (#7962), so default to 32-bit should be good for most situations.

[geezmolycos]

Also, as a further suggestion, it might be straightforward to also support DWARF generation for windows target (COFF object) with these options. As mentioned in CodeLLDB's wiki page, LLDB's support for CodeView is incomplete, and GDB currently has no support for Codeview.

Allowing DWARF generation for windows could make it easier to integrate with mingw toolchain (which uses GDB or LLDB) and to debug zig program in Wine environment

[chrisbodhi]

@geezmolycos I made a pass at adding DWARF support for COFF objects as you suggested, but with my limited time, wasn't able to come up with a good emulation solution for verifying my changes. I'd prefer to add a new issue for adding DWARF support for COFF objects, and get this code reviewed as is. How does that all sound to you?

[geezmolycos]

Okay, the current solution should be fine for the original problem. I know that the COFF thing might need more reviewing and testing. I will look into that and post another issue to find help or try to work with that myself. Anyways, thanks for your contribution

[chrisbodhi]

Thanks for all of your guidance, @geezmolycos, and for writing a detailed & helpful issue -- that made it much easier to contribute. :D

[chrisbodhi]

@kubkon 👋 Pinging for a review, since you've previously reviewed a different, related PR.

[chrisbodhi]

@andrewrk 👋 Pinging for a review