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.debug_line: don't rely on header_length field

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Empirically, debug info consumers do not respect this field, or otherwise
consider it to be an error when it does not point exactly to the end of the header.
Therefore we rely on the NOP jump at the beginning of the Line Number Program for
padding rather than this field.

llvm-dwarfdump says the line number data is fine; gdb and
binutils-readelf crap out.
This commit is contained in:
Andrew Kelley
2020-08-02 19:57:42 -07:00
parent 1a3f250f19
commit 1ce6e201aa
1 changed files with 20 additions and 3 deletions
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23
src-self-hosted/link.zig
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@@ -647,6 +647,8 @@ pub const File = struct {
}
fn allocatedSize(self: *Elf, start: u64) u64 {
if (start == 0)
return 0;
var min_pos: u64 = std.math.maxInt(u64);
if (self.shdr_table_offset) |off| {
if (off > start and off < min_pos) min_pos = off;
@@ -1229,8 +1231,13 @@ pub const File = struct {
0, // segment_selector_size
});
const header_length = dbg_line_prg_off - (di_buf.items.len + ptr_width_bytes);
self.writeDwarfAddrAssumeCapacity(&di_buf, header_length);
// Empirically, debug info consumers do not respect this field, or otherwise
// consider it to be an error when it does not point exactly to the end of the header.
// Therefore we rely on the NOP jump at the beginning of the Line Number Program for
// padding rather than this field.
const before_header_len = di_buf.items.len;
di_buf.items.len += ptr_width_bytes; // We will come back and write this.
const after_header_len = di_buf.items.len;
const opcode_base = DW.LNS_set_isa + 1;
di_buf.appendSliceAssumeCapacity(&[_]u8{
@@ -1280,7 +1287,17 @@ pub const File = struct {
self.writeDwarfAddrAssumeCapacity(&di_buf, root_src_file_strp); // DW.LNCT_path, DW.FORM_strp
di_buf.appendAssumeCapacity(0); // LNCT_directory_index, FORM_data1
// Add a redundant NOP in case the consumer ignores header_length.
const header_len = di_buf.items.len - after_header_len;
switch (self.ptr_width) {
.p32 => {
mem.writeInt(u32, di_buf.items[before_header_len..][0..4], @intCast(u32, header_len), target_endian);
},
.p64 => {
mem.writeInt(u64, di_buf.items[before_header_len..][0..8], header_len, target_endian);
},
}
// We use a NOP jmp because consumers empirically do not respect the header length field.
const after_jmp = di_buf.items.len + 6;
if (after_jmp > dbg_line_prg_off) {
// Move the first N files to the end to make more padding for the header.