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dwarf: refactor routine for precalculating size of dbg line header

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This commit is contained in:
Jakub Konka 2022-12-07 22:29:07 +01:00
parent 6817219e27
commit 62145a1b08
1 changed files with 22 additions and 17 deletions
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39
src/link/Dwarf.zig
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@ -2303,7 +2303,6 @@ pub fn writeDbgLineHeader(self: *Dwarf, module: *Module) !void {
// files, and padding. We have a function to compute the upper bound size, however,
// because it's needed for determining where to put the offset of the first `SrcFn`.
const needed_bytes = self.dbgLineNeededHeaderBytes(paths.dirs, paths.files);
log.debug("dbg_line_prg_off = {x}, needed_bytes = {x}", .{ dbg_line_prg_off, needed_bytes });
var di_buf = try std.ArrayList(u8).initCapacity(self.allocator, needed_bytes);
defer di_buf.deinit();
@ -2390,6 +2389,8 @@ pub fn writeDbgLineHeader(self: *Dwarf, module: *Module) !void {
},
}
assert(needed_bytes == di_buf.items.len);
// We use NOPs because consumers empirically do not respect the header length field.
if (di_buf.items.len > dbg_line_prg_off) {
// Move the first N files to the end to make more padding for the header.
@ -2448,27 +2449,31 @@ fn ptrWidthBytes(self: Dwarf) u8 {
}
fn dbgLineNeededHeaderBytes(self: Dwarf, dirs: []const []const u8, files: []const []const u8) u32 {
_ = self;
const directory_entry_format_count = 1;
const file_name_entry_format_count = 1;
const directory_count = dirs.len + 1;
const file_name_count = files.len;
var size = switch (self.bin_file.tag) { // length field
.macho => @sizeOf(u32),
else => switch (self.ptr_width) {
.p32 => @as(usize, @sizeOf(u32)),
.p64 => @sizeOf(u32) + @sizeOf(u64),
},
};
size += @sizeOf(u16); // version field
size += switch (self.bin_file.tag) { // offset to end-of-header
.macho => @sizeOf(u32),
else => self.ptrWidthBytes(),
};
size += 18; // opcodes
var dir_names_len: usize = 0;
for (dirs) |dir| {
dir_names_len += dir.len + 1;
for (dirs) |dir| { // include dirs
size += dir.len + 1;
}
size += 1; // include dirs sentinel
var file_names_len: usize = 0;
for (files) |file| {
file_names_len += file.len + 1;
for (files) |file| { // file names
size += file.len + 1 + 1 + 1 + 1;
}
size += 1; // file names sentinel
return @intCast(u32, 53 + directory_entry_format_count * 2 + file_name_entry_format_count * 2 +
directory_count * 8 + file_name_count * 8 +
// These are encoded as DW.FORM.string rather than DW.FORM.strp as we would like
// because of a workaround for readelf and gdb failing to understand DWARFv5 correctly.
dir_names_len + file_names_len);
return @intCast(u32, size);
}
/// The reloc offset for the line offset of a function from the previous function's line.