[PATCH] D49446: [WebAssembly] Move .debug_line section address of dead function outside section range

[Yury Delendik via Phabricator via llvm-commits]

yurydelendik added a comment.

In https://reviews.llvm.org/D49446#1167210, @sbc100 wrote:

> I'm still not sure I understand why writing zero here is not a good idea.


It will be probably easy to demonstrate on the example. When running the test case (test/wasm/debug-removed-fn.ll) without the patch, the .debug_line data contains the following info

  0x0000000000000005      1      0      1   0             0  is_stmt
  0x0000000000000008      2      3      1   0             0  is_stmt prologue_end
  0x0000000000000009      2      3      1   0             0  is_stmt end_sequence
  0x0000000000000000      5      0      1   0             0  is_stmt
  0x0000000000000003      6      3      1   0             0  is_stmt prologue_end
  0x0000000000000004      6      3      1   0             0  is_stmt end_sequence

With patch:

  0x0000000000000005      1      0      1   0             0  is_stmt
  0x0000000000000008      2      3      1   0             0  is_stmt prologue_end
  0x0000000000000009      2      3      1   0             0  is_stmt end_sequence
  0x00000000fdead000      5      0      1   0             0  is_stmt
  0x00000000fdead003      6      3      1   0             0  is_stmt prologue_end
  0x00000000fdead004      6      3      1   0             0  is_stmt end_sequence

Notice that the "bar" function debug data "claims" that the function can be found at addresses 0-4 (without the patch). Then same true for .debug_info.

If the both functions are exported, .debug_line looks like:

  0x0000000000000005      1      0      1   0             0  is_stmt
  0x0000000000000008      2      3      1   0             0  is_stmt prologue_end
  0x0000000000000009      2      3      1   0             0  is_stmt end_sequence
  0x000000000000000a      5      0      1   0             0  is_stmt
  0x000000000000000d      6      3      1   0             0  is_stmt prologue_end
  0x000000000000000e      6      3      1   0             0  is_stmt end_sequence

Does this explain the problem?


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D49446