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[WebAssembly] Add --export flag to force a symbol to be exported 

This is useful for emscripten or other tools that want to
selectively exports symbols without necessarily changing the
source code.

Differential Revision: https://reviews.llvm.org/D42003

llvm-svn: 322408
This commit is contained in:
Sam Clegg 2018-01-12 22:10:35 +00:00
parent 6371180cd4
commit 2a06afae16
5 changed files with 54 additions and 4 deletions
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29
lld/test/wasm/export.ll Normal file
View File

@ -0,0 +1,29 @@
; RUN: llc -filetype=obj -mtriple=wasm32-unknown-unknown-wasm %s -o %t.o
; RUN: not lld -flavor wasm --export=missing -o %t.wasm %t.o 2>&1 | FileCheck -check-prefix=CHECK-ERROR %s
; RUN: lld -flavor wasm --export=hidden_function -o %t.wasm %t.o
; RUN: obj2yaml %t.wasm | FileCheck %s
define hidden i32 @hidden_function() local_unnamed_addr {
entry:
ret i32 0
}
define i32 @_start() local_unnamed_addr {
entry:
ret i32 0
}
; CHECK-ERROR: error: symbol exported via --export not found: missing
; CHECK: - Type: EXPORT
; CHECK-NEXT: Exports:
; CHECK-NEXT: - Name: memory
; CHECK-NEXT: Kind: MEMORY
; CHECK-NEXT: Index: 0
; CHECK-NEXT: - Name: _start
; CHECK-NEXT: Kind: FUNCTION
; CHECK-NEXT: Index: 1
; CHECK-NEXT: - Name: hidden_function
; CHECK-NEXT: Kind: FUNCTION
; CHECK-NEXT: Index: 0
; CHECK-NEXT: - Type: CODE

17
lld/wasm/Driver.cpp
View File

@ -296,8 +296,8 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
addSyntheticUndefinedFunction(Config->Entry, &Signature);
// Handle the `--undefined <sym>` options.
for (StringRef S : args::getStrings(Args, OPT_undefined))
addSyntheticUndefinedFunction(S, nullptr);
for (auto* Arg : Args.filtered(OPT_undefined))
addSyntheticUndefinedFunction(Arg->getValue(), nullptr);
Config->CtorSymbol = Symtab->addDefinedFunction(
"__wasm_call_ctors", &Signature, WASM_SYMBOL_VISIBILITY_HIDDEN);
@ -321,8 +321,8 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
// -u/--undefined since these undefined symbols have only names and no
// function signature, which means they cannot be written to the final
// output.
for (StringRef S : args::getStrings(Args, OPT_undefined)) {
Symbol *Sym = Symtab->find(S);
for (auto* Arg : Args.filtered(OPT_undefined)) {
Symbol *Sym = Symtab->find(Arg->getValue());
if (!Sym->isDefined())
error("function forced with --undefined not found: " + Sym->getName());
}
@ -330,6 +330,15 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
if (errorCount())
return;
for (auto *Arg : Args.filtered(OPT_export)) {
Symbol *Sym = Symtab->find(Arg->getValue());
if (!Sym || !Sym->isDefined())
error("symbol exported via --export not found: " +
Twine(Arg->getValue()));
else
Sym->setHidden(false);
}
if (!Config->Entry.empty() && !Symtab->find(Config->Entry)->isDefined())
error("entry point not found: " + Config->Entry);
if (errorCount())

3
lld/wasm/Options.td
View File

@ -74,6 +74,9 @@ def error_limit: J<"error-limit=">,
// The follow flags are unique to wasm
defm export: Eq<"export">,
HelpText<"Force a symbol to be exported">;
def global_base: J<"global-base=">,
HelpText<"Where to start to place global data">;

8
lld/wasm/Symbols.cpp
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@ -97,6 +97,14 @@ bool Symbol::isHidden() const {
return (Flags & WASM_SYMBOL_VISIBILITY_MASK) == WASM_SYMBOL_VISIBILITY_HIDDEN;
}
void Symbol::setHidden(bool IsHidden) {
Flags &= ~WASM_SYMBOL_VISIBILITY_MASK;
if (IsHidden)
Flags |= WASM_SYMBOL_VISIBILITY_HIDDEN;
else
Flags |= WASM_SYMBOL_VISIBILITY_DEFAULT;
}
std::string lld::toString(const wasm::Symbol &Sym) {
if (Config->Demangle)
if (Optional<std::string> S = demangleItanium(Sym.getName()))

1
lld/wasm/Symbols.h
View File

@ -67,6 +67,7 @@ public:
bool hasFunctionType() const { return FunctionType != nullptr; }
const WasmSignature &getFunctionType() const;
void setFunctionType(const WasmSignature *Type);
void setHidden(bool IsHidden);
uint32_t getOutputIndex() const;