[all-commits] [llvm/llvm-project] d64efe: [lld-macho] Remove symbols to `__mod_init_func` wi...

[Daniel Bertalan via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: d64efe42eb98af76ba4ba26f48d079713f513af9
      https://github.com/llvm/llvm-project/commit/d64efe42eb98af76ba4ba26f48d079713f513af9
  Author: Daniel Bertalan <dani at danielbertalan.dev>
  Date:   2024-07-06 (Sat, 06 Jul 2024)

  Changed paths:
    M lld/MachO/Driver.cpp
    M lld/MachO/Writer.cpp
    M lld/test/MachO/init-offsets.s
    A lld/test/MachO/invalid/init-offsets.s

  Log Message:
  -----------
  [lld-macho] Remove symbols to `__mod_init_func` with `-init_offsets` (#97156)

When `-fixup_chains`/`-init_offsets` is used, a different section,
`__init_offsets` is synthesized from `__mod_init_func`. If there are any
symbols defined inside `__mod_init_func`, they are added to the symbol
table unconditionally while processing the input files. Later, when
querying these symbols' addresses (when constructing the symtab or
exports trie), we crash with a null deref, as there is no output section
assigned to them.

Just making the symbols point to `__init_offsets` is a bad idea, as the
new section stores 32-bit integers instead of 64-bit pointers; accessing
the symbols would not do what the programmer intended. We should
entirely omit them from the output. This is what ld64 and ld-prime do.

This patch uses the same mechanism as dead-stripping to mark these
symbols as not needed in the output. There might be nicer fixes than the
workaround, this is discussed in #97155.

Fixes https://github.com/llvm/llvm-project/pull/79894#issuecomment-1944092892
Fixes #94716



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