[PATCH] D42237: [WebAssembly] Symbol changes #4b: export stack-pointer, LLD only
Nicholas Wilson via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Thu Jan 18 02:42:10 PST 2018
ncw created this revision.
ncw added reviewers: sbc100, sunfish.
Herald added subscribers: llvm-commits, aheejin, jgravelle-google, dschuff, jfb.
Split out of https://reviews.llvm.org/D41955.
This solves the problem that `--emit-relocs` needs the stack-pointer to be exported, in order to write out any relocations that reference the `__stack_pointer` symbol by its symbol index.
Rationale: `--emit-relocs` is only ever going to be used by downstream tools (such as Emscripten's binaryen tools). In particular, we don't expect that the output from `--emit-relocs` will be sent to browsers without further post-processing. Although browsers don't allow mutable globals to be imported/exported (yet), tools like binaryen do accept it.
Repository:
rLLD LLVM Linker
https://reviews.llvm.org/D42237
Files:
test/wasm/stack-pointer.ll
wasm/Writer.cpp
Index: wasm/Writer.cpp
===================================================================
--- wasm/Writer.cpp
+++ wasm/Writer.cpp
@@ -658,8 +658,10 @@
for (const Symbol *Sym : DefinedGlobals) {
// Can't export the SP right now because it's mutable and mutable globals
- // cannot be exported.
- if (Sym == Config->StackPointerSymbol)
+ // cannot be exported. However, for output that's intended for processing
+ // by downstream tools, we can rely on the "mutable global" proposal
+ // being present.
+ if (Sym == Config->StackPointerSymbol && !Config->EmitRelocs)
continue;
ExportedSymbols.emplace_back(WasmExportEntry{Sym, BudgeName(Sym)});
}
Index: test/wasm/stack-pointer.ll
===================================================================
--- test/wasm/stack-pointer.ll
+++ test/wasm/stack-pointer.ll
@@ -58,6 +58,9 @@
; CHECK-NEXT: - Name: __wasm_call_ctors
; CHECK-NEXT: Kind: FUNCTION
; CHECK-NEXT: Index: 1
+; CHECK-NEXT: - Name: __stack_pointer
+; CHECK-NEXT: Kind: GLOBAL
+; CHECK-NEXT: Index: 0
; CHECK-NEXT: - Name: __heap_base
; CHECK-NEXT: Kind: GLOBAL
; CHECK-NEXT: Index: 1
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