nid_patcher turns the _nid_postfix names of a library into NIDs for ELF
and PE. A library built on macOS is a Mach-O dylib, whose exports are in
a dyld export trie and whose imports are in the chained fixups, so it
gets its own patcher.
- The export trie is read, every exported C name (without Mach-O's
leading underscore) is resolved to its NID, and the trie is rebuilt the
way ld64 lays it out: the offsets are uleb128, so the layout is repeated
until it is stable. A trie that no longer fits is appended to
__LINKEDIT, which has to end the file, and a signed image is refused.
- Weak definitions that are not marked _nid_postfix or _nid_no_patch keep
their names: dyld coalesces those across images by name.
- In the chained imports, names bound to a .prx dylib that are guest
facing (a _nid_postfix name or an sce prefix) are patched in place; a
name that would grow, or that shares storage with another import, is an
error. Images that use bind opcodes instead of chained fixups are
refused.
- ExportExclusions reads the exports of a reference Mach-O, so the
exclusion list works for libraries built on macOS as well.
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