[PATCH] D66279: [ELF] Make LinkerScript::assignAddresses iterative

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

Investigated a bit how ld.bfd works.

  SECTIONS {
    . = 0x1000;
    a = b + 1; b = c + 1; c = d + 1; d = e + 1; e = f + 1; f = g + 1; g = h + 1; h = .;
  }
  // ld/ld-new -T a.lds a.o -o a
  // undefined symbol `b' referenced in expression
  
  SECTIONS {
    . = 0x1000;
    a = b + 1; b = c + 1; c = d + 1; d = e + 1; e = f + 1; f = g + 1; g = .;
  }
  // st_value(a) is incorrect 6, not 0x1006.
  
  // st_value(a) is correct (0x1005) with one less variable.

In either case, `lang_do_assignments` ran 3 times.

- lang_do_assignments (lang_mark_phase_enum); // in ld/ldlang.c:lang_process
- lang_do_assignments (lang_assigning_phase_enum); // in ld/ldlang.c:lang_relax_sections
- lang_do_assignments (lang_final_phase_enum); // in ld/ldlang.c:lang_process

The initial 3 calls allow it to compute a slightly longer chain, though a new `lang_do_assignments (lang_assigning_phase_enum);` only allows it to compute the case with one more variable. The iterative process we use can emulate its behavior.


Repository:
  rLLD LLVM Linker

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  https://reviews.llvm.org/D66279/new/

https://reviews.llvm.org/D66279