[PATCH] D126950: [lld][WebAssembly] Retain data segments referenced via __start/__stop

[Sam Clegg via Phabricator via llvm-commits]

sbc100 added inline comments.


================
Comment at: lld/wasm/MarkLive.cpp:121
+      if (symtab->find(("__start_" + name).str()) ||
+          symtab->find(("__stop_" + name).str())) {
+        enqueueWholeChunk(segment);
----------------
kateinoigakukun wrote:
> sbc100 wrote:
> > So, does this mean that if I reference the symbol `__start_data`, then all the normal data segment in my whole program will be included (non will be GC'd)?
> > 
> > Is this how ELF works?  It seems like a shame to loose the ability to GC data segments just because i want to know where my data starts and/or stops.  I suppose we have other symbols such as `_edata` which can be used to get the start/end of the static data region without disabling GC?
> > So, does this mean that if I reference the symbol __start_data, then all the normal data segment in my whole program will be included (non will be GC'd)?
> 
> Yes, I agree that's unfortunate situation...
> 
> > Is this how ELF works? 
> 
> To be precise, according to https://lld.llvm.org/ELF/start-stop-gc, whether `__start`/`__stop` symbols retain all input data segments is controlled by `-z start-stop-gc` / `-z nostart-stop-gc`.
> 
> The latest ELF lld defaults to `-z start-stop-gc`, but GNU ld defaults to `-z nostart-stop-gc` to be conservative.
> 
> So, how about adding the option in wasm-ld also? If it's reasonable, which behavior should be defaulted?
Yes, adding start-stop-gc as part of this change makes sense to me.

So simplify this you could split out of the moving of the getOutputDataSegmentName function amd land that first?  It seems like a good refactoring anyway.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D126950/new/

https://reviews.llvm.org/D126950