Add -fdebuginfo option

[leroycep]

Builds on pull request #22077, adding a convenient way to get symbol based stack traces to the Zig compiler and build system.

• Adds -fdebuginfo= option (to?)
• Removes -fstrip option (from?)
• Removes -gdwarf32 and gdwarf64
• use -g<debug stuff> or --debug <debug stuff> instead of -fdebuginfo to match with clang and gcc?
• check that -fdebuginfo reports useful errors if an option isn't supported for the target platform?
• Rewrite commits to make better individual changes?

See also #18520

This work is licensed on the same terms as the Zig project.

Copyright © 2024 TigerBeetle, Inc.

This code was written under contract for TigerBeetle. As a work made for hire, authorship and copyright goes to TigerBeetle.

Author certificate

LeRoyce Pearson <opensource@geemili.xyz> [TigerBeetle, Inc.]

This work is licensed on the same terms as this project (Zig).

[alexrp]

cc @andrewrk

I'd personally like to see something like:

Suggested change

	\\ -fdebuginfo=[format] Set strip level
	\\ none Don't emit any debug info
	\\ symbols Emit symbol table
	\\ dwarf32 Emit dwarf32 debug info
	\\ dwarf64 Emit dwarf32 debug info
	\\ code_view (Windows) Emit code_view debug info
	\\ -g Emit debug info
	\\ -g0 Don't emit debug info
	\\ -g[format] Override target debug format
	\\ symbols Only use the object format's symbol table
	\\ dwarf32 Use 32-bit DWARF
	\\ dwarf64 Use 64-bit DWARF
	\\ codeview (Windows) Use CodeView

-g would pick whatever format is native to the target, so 32-bit DWARF for most targets and CodeView for Windows. -g<format> should imply -g.

If no option is given, I suggest the defaults should be:

• Full native debug info for Debug and ReleaseSafe.
• Symbol table debug info for ReleaseFast.
• No debug info at all for ReleaseSmall. (This is in line with the decision to omit frame pointers in compiler: Only omit frame pointers by default for ReleaseSmall #22180.)

[leroycep]

I agree with this. In the initial implementation I was a bit too focused on putting everything into DebugFormat. User facing we need a bit more information than that, especially if later on Zig gains support for generating partial debug info.

Another consideration: some debug formats are not mutually exclusive. DWARF is already a superset of symbols, and CTF can live alongside DWARF. So a set of independent values may make more sense than the enum I introduced here.

Perhaps something like:

 -g          Emit debug info
 -g0         Don't emit debug info
 -gsymbols   Emit symbol table
 -gsymbols0  Don't emit symbol table
 -gdwarf     Emit DWARF debug info
 -gdwarf0    Don't emit DWARF debug info
 -gcodeview  Emit Code View debug info
 -gcodeview0 Don't emit Code View debug info

Then the user input side data structure would look like:

const DebugSettings = struct {
    emit_debug_info: ?bool,
    emit_debug_format_symbols: ?bool,
    emit_debug_format_dwarf: ?bool,
    emit_debug_format_codeview: ?bool,
};

With defaults resolution like so:

const DebugConfig = struct {
    emit_symbols: bool,
    emit_dwarf: ?DwarfFormat,
    emit_codeview: bool,
};

fn (debug_settings: DebugSettings) DebugConfig {
    if (debug_settings.emit_debug_info) |should_emit| {
        if (!should_emit) DebugConfig{ .emit_symbols = false, .emit_dwarf = null, .emit_codeview = false };
    }
    const debug_format_is_selected = debug_settings.emit_debug_format_symbols != null or debug_settings.emit_debug_format_dwarf != null or debug_settings.emit_debug_format_codeview != null;

    const emit_symbols = blk: {
        if (debug_settings.emit_debug_format_symbols) |should_emit| break :blk should_emit;
        if (debug_format_is_selected) break :blk false;
        // TODO: check release mode, output format, etc.
        break :blk true;
    };

    const emit_dwarf_format = blk: {
        // TODO: look at -gdwarf32 and -gdwarf64 flags
        if (debug_settings.emit_debug_format_dwarf) |should_emit| break :blk if (should_emit) .dwarf32 else null;
        if (debug_format_is_selected) break :blk null;
        // TODO: check release mode, output format, etc.
        break :blk null;
    };

    const emit_codeview = blk: {
        if (debug_settings.emit_debug_format_symbols) |should_emit| break :blk should_emit;
        if (debug_format_is_selected) break :blk false;
        // TODO: check release mode, output format, etc.
        break :blk false;
    };

    return DebugConfig{ .emit_symbols = emit_symbols, .emit_dwarf = emit_dwarf_format, .emit_codeview = emit_codeview };
}

But maybe I'm over complicating this; I'm not sure if Zig wants to support generating multiple debug formats even if it is technically possible.

[alexrp]

It seems useful to combine BTF/CTF with DWARF; GCC supports this. I'm not convinced that combining DWARF and CodeView is useful, nor that emitting DWARF/CodeView but omitting the symbol table is useful. But maybe I'm missing some use case here?

Assuming I'm not, then I think we can just add -gctf and -gctf-dwarf32/-gctf-dwarf64 options in the future if we add CTF support.