[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#1172887, @dblaikie wrote:

> Ish - but existing debuggers/linkers already tolerate this sort of debug info - so it'd be ideal/better if WAsm did too. Any address derived from zero would be considered invalid/uninteresting. (similarly for the debug_info itself - you'd find similarly confusing data, where functions start at zero and are X bytes long - so technically a bunch of non-zero bytes are covered by that range, but currently it seems existing debuggers/linkers are OK with this contract too).


Currently, the wasm function (dead or alive) never starts from 0. The `Sym->Function->getFunctionCodeOffset()` returns size of the function size field that is placed before function body. If we want debug info to point strict 0, we can change the `DEAD_FUNCTION_OFFSET` to be 0 -- the rest of the patch will stay pretty much the same. I just took one step further and moved that completely on of code range -- with other platforms that's happening automatically since PC is almost never close to 0.

FWIW, the algorithm for the detection of dead function debug entries looks like https://github.com/kripken/emscripten/pull/6884/files#diff-d7e06c82407a72c0476db85b2cf5d3deR157 and requires linker to produce compact LEB values for functions size field length.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D49446