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[lld][WebAssembly] Allow exporting of mutable globals

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In particular allow explict exporting of `__stack_pointer` but
exclud this from `--export-all` to avoid requiring the mutable
globals feature whenenve `--export-all` is used.

This uncovered a bug in populateTargetFeatures regarding checking
if the mutable-globals feature is allowed.

See: https://github.com/WebAssembly/binaryen/issues/2934

Differential Revision: https://reviews.llvm.org/D88506
This commit is contained in:
Sam Clegg
2020-07-30 17:44:32 -07:00
parent 93a1fc2e18
commit 3c45a06f26
4 changed files with 101 additions and 7 deletions
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15
lld/wasm/Writer.cpp
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@@ -453,7 +453,7 @@ void Writer::populateTargetFeatures() {
if (!config->checkFeatures)
return;
if (!config->relocatable && used.count("mutable-globals") == 0) {
if (!config->relocatable && allowed.count("mutable-globals") == 0) {
for (const Symbol *sym : out.importSec->importedSymbols) {
if (auto *global = dyn_cast<GlobalSymbol>(sym)) {
if (global->getGlobalType()->Mutable) {
@@ -571,12 +571,13 @@ void Writer::calculateExports() {
}
export_ = {name, WASM_EXTERNAL_FUNCTION, f->getFunctionIndex()};
} else if (auto *g = dyn_cast<DefinedGlobal>(sym)) {
// TODO(sbc): Remove this check once to mutable global proposal is
// implement in all major browsers.
// See: https://github.com/WebAssembly/mutable-global
if (g->getGlobalType()->Mutable) {
// Only __stack_pointer and __tls_base should ever be create as mutable.
assert(g == WasmSym::stackPointer || g == WasmSym::tlsBase);
if (g->getGlobalType()->Mutable && !g->getFile() && !g->forceExport) {
// Avoid exporting mutable globals are linker synthesized (e.g.
// __stack_pointer or __tls_base) unless they are explicitly exported
// from the command line.
// Without this check `--export-all` would cause any program using the
// stack pointer to export a mutable global even if none of the input
// files were built with the `mutable-globals` feature.
continue;
}
export_ = {name, WASM_EXTERNAL_GLOBAL, g->getGlobalIndex()};