getLineNumberInfo

pub fn getLineNumberInfo(self: *Pdb, gpa: Allocator, module: *Module, address: u64) !std.debug.SourceLocation {
    std.debug.assert(module.populated);
    const subsect_info = module.subsect_info;

    var sect_offset: usize = 0;
    var skip_len: usize = undefined;
    while (sect_offset != subsect_info.len) : (sect_offset += skip_len) {
        const subsect_hdr: *align(1) pdb.DebugSubsectionHeader = @ptrCast(&subsect_info[sect_offset]);
        skip_len = subsect_hdr.length;
        sect_offset += @sizeOf(pdb.DebugSubsectionHeader);

        switch (subsect_hdr.kind) {
            .lines => {
                var line_index = sect_offset;

                const line_hdr: *align(1) pdb.LineFragmentHeader = @ptrCast(&subsect_info[line_index]);
                if (line_hdr.reloc_segment == 0)
                    return error.MissingDebugInfo;
                line_index += @sizeOf(pdb.LineFragmentHeader);
                const frag_vaddr_start = line_hdr.reloc_offset;
                const frag_vaddr_end = frag_vaddr_start + line_hdr.code_size;

                if (address >= frag_vaddr_start and address < frag_vaddr_end) {
                    // There is an unknown number of LineBlockFragmentHeaders (and their accompanying line and column records)
                    // from now on. We will iterate through them, and eventually find a SourceLocation that we're interested in,
                    // breaking out to :subsections. If not, we will make sure to not read anything outside of this subsection.
                    const subsection_end_index = sect_offset + subsect_hdr.length;

                    while (line_index < subsection_end_index) {
                        const block_hdr: *align(1) pdb.LineBlockFragmentHeader = @ptrCast(&subsect_info[line_index]);
                        line_index += @sizeOf(pdb.LineBlockFragmentHeader);
                        const start_line_index = line_index;

                        const has_column = line_hdr.flags.have_columns;

                        // All line entries are stored inside their line block by ascending start address.
                        // Heuristic: we want to find the last line entry
                        // that has a vaddr_start <= address.
                        // This is done with a simple linear search.
                        var line_i: u32 = 0;
                        while (line_i < block_hdr.num_lines) : (line_i += 1) {
                            const line_num_entry: *align(1) pdb.LineNumberEntry = @ptrCast(&subsect_info[line_index]);
                            line_index += @sizeOf(pdb.LineNumberEntry);

                            const vaddr_start = frag_vaddr_start + line_num_entry.offset;
                            if (address < vaddr_start) {
                                break;
                            }
                        }

                        // line_i == 0 would mean that no matching pdb.LineNumberEntry was found.
                        if (line_i > 0) {
                            const file_name = try self.getFileName(gpa, module, block_hdr.name_index);
                            errdefer gpa.free(file_name);

                            const line_entry_idx = line_i - 1;

                            const column = if (has_column) blk: {
                                const start_col_index = start_line_index + @sizeOf(pdb.LineNumberEntry) * block_hdr.num_lines;
                                const col_index = start_col_index + @sizeOf(pdb.ColumnNumberEntry) * line_entry_idx;
                                const col_num_entry: *align(1) pdb.ColumnNumberEntry = @ptrCast(&subsect_info[col_index]);
                                break :blk col_num_entry.start_column;
                            } else 0;

                            const found_line_index = start_line_index + line_entry_idx * @sizeOf(pdb.LineNumberEntry);
                            const line_num_entry: *align(1) pdb.LineNumberEntry = @ptrCast(&subsect_info[found_line_index]);

                            return .{
                                .file_name = file_name,
                                .line = line_num_entry.flags.start,
                                .column = column,
                            };
                        }
                    }

                    // Checking that we are not reading garbage after the (possibly) multiple block fragments.
                    if (line_index != subsection_end_index) {
                        return error.InvalidDebugInfo;
                    }
                }
            },
            else => {},
        }

        if (sect_offset > subsect_info.len)
            return error.InvalidDebugInfo;
    }

    return error.MissingDebugInfo;
}