[PATCH] D130725: [lld/mac] Add support for $ld$previous symbols with explicit symbol name

[Nico Weber via Phabricator via llvm-commits]

thakis created this revision.
thakis added a reviewer: lld-macho.
Herald added projects: lld-macho, All.
thakis requested review of this revision.

A symbol `$ld$previous$/Another$1.2.3$1$3.0$14.0$_xxx$` means
"pretend symbol `_xxx` is in dylib `/Another` with version `1.2.3`
if the deployment target is between `3.0` and `14.0` and we're
targeting platform `1` (ie macOS)".

This means dylibs can now inject synthetic dylibs into the link, so
DylibFile needs to grow a 3rd constructor.

The only other interesting thing is that such an injected dylib
counts as a use of the original dylib. This patch gets this mostly
right (if _only_ `$ld$previous` symbols are used from a dylib,
we don't add a dep on the dylib itself, matching ld64), but one case
where we don't match ld64 yet is that ld64 even omits the original
dylib when linking it with `-needed-l`. Lld currently still adds a load
command for the original dylib in that case. (That's for a future
patch.)

Fixes #56074.


https://reviews.llvm.org/D130725

Files:
  lld/MachO/InputFiles.cpp
  lld/MachO/InputFiles.h
  lld/MachO/Writer.cpp
  lld/test/MachO/special-symbol-ld-previous.s

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