[lld] [llvm] [lld][MachO] Follow-up to use madvise() for threaded file page-in. (PR #157917)

[Daniel Rodríguez Troitiño via llvm-commits]

drodriguez wrote:

@zygoloid I cannot find an online link, but for example, in my macOS 15.6.1, `man mmap` has the following text:

```
Any extension beyond the end of the mapped object will be zero-filled.
```

And there's no `BUGS` section in there. I think this workaround might not me needed for macOS, and maybe by reading the buffer end byte, the access pattern has changed enough to have performance implications. It might be creating a page fault, if the file size is the right one to fall in a page boundary.

@johnno1962 : I have checked the YAML/JSON parsers for the tbd and they seem to check for the length of the files and not blindly searching for the end of the string. I cannot say those are the only textual files that are processed (linker scripts files and similar might be accepted?). If you have executed the test suite and nothing pops, maybe this is correct, but the situation described in #152595 is not something that can be replicated easily in the tests, so this might be introducing problems.

https://github.com/llvm/llvm-project/pull/157917