Apple devtools use this to locate the dSYM files for a given
binary.
The UUID is computed based on an MD5 hash of the binary's contents. In order to
hash the contents, we must first write them, but LC_UUID itself must be part of
the written contents in order for all the offsets to be calculated correctly.
We resolve this circular paradox by first writing an LC_UUID with an all-zero
UUID, then updating the UUID with its real value later.
I'm not sure there's a good way to test that the value of the UUID is
"as expected", so I've just checked that it's present.
Reviewed By: #lld-macho, compnerd, smeenai
Differential Revision: https://reviews.llvm.org/D89418
ld64 is cool with leading `0x` for hex command-line args, and we should be also.
Reviewed By: #lld-macho, int3
Differential Revision: https://reviews.llvm.org/D88065
Tools like `install_name_tool` and `codesign` may modify the Mach-O
header and increase its size. The linker has to provide padding to make this
possible. This diff does that, plus sets its default value to 32 bytes (which
is what ld64 does).
Unlike ld64, however, we lay out our sections *exactly* `-headerpad` bytes from
the header, whereas ld64 just treats the padding requirement as a lower bound.
ld64 actually starts laying out the non-header sections in the __TEXT segment
from the end of the (page-aligned) segment rather than the front, so its
binaries typically have more than `-headerpad` bytes of actual padding.
We should consider implementing the same alignment behavior.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D84714
Jez Ng