[lld] r327151 - [WebAssembly] Handle weak undefined functions with a synthetic stub
Nicholas Wilson via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 9 09:06:38 PST 2018
Author: ncw
Date: Fri Mar 9 09:06:38 2018
New Revision: 327151
URL: http://llvm.org/viewvc/llvm-project?rev=327151&view=rev
Log:
[WebAssembly] Handle weak undefined functions with a synthetic stub
This error case is described in Linking.md. The operand for call requires
generation of a synthetic stub.
Differential Revision: https://reviews.llvm.org/D44028
Added:
lld/trunk/test/wasm/undefined-weak-call.ll
Modified:
lld/trunk/wasm/Driver.cpp
lld/trunk/wasm/InputFiles.cpp
lld/trunk/wasm/MarkLive.cpp
lld/trunk/wasm/Symbols.cpp
lld/trunk/wasm/Symbols.h
Added: lld/trunk/test/wasm/undefined-weak-call.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/wasm/undefined-weak-call.ll?rev=327151&view=auto
==============================================================================
--- lld/trunk/test/wasm/undefined-weak-call.ll (added)
+++ lld/trunk/test/wasm/undefined-weak-call.ll Fri Mar 9 09:06:38 2018
@@ -0,0 +1,117 @@
+; RUN: llc -filetype=obj %s -o %t.o
+; RUN: wasm-ld --check-signatures --no-entry %t.o -o %t.wasm
+; RUN: obj2yaml %t.wasm | FileCheck %s
+
+; Check that calling an undefined weak function generates an appropriate stub
+; that will fail at runtime with "unreachable".
+
+target triple = "wasm32-unknown-unknown-wasm"
+
+declare extern_weak void @weakFunc1()
+declare extern_weak void @weakFunc2() ; same signature
+declare extern_weak void @weakFunc3(i32 %arg) ; different
+declare extern_weak void @weakFunc4() ; should be GC'd as not called
+
+define i32 @callWeakFuncs() {
+ call void @weakFunc1()
+ call void @weakFunc2()
+ call void @weakFunc3(i32 2)
+ %addr1 = ptrtoint void ()* @weakFunc1 to i32
+ %addr4 = ptrtoint void ()* @weakFunc4 to i32
+ %sum = add i32 %addr1, %addr4
+ ret i32 %sum
+}
+
+; CHECK: --- !WASM
+; CHECK-NEXT: FileHeader:
+; CHECK-NEXT: Version: 0x00000001
+; CHECK-NEXT: Sections:
+; CHECK-NEXT: - Type: TYPE
+; CHECK-NEXT: Signatures:
+; CHECK-NEXT: - Index: 0
+; CHECK-NEXT: ReturnType: I32
+; CHECK-NEXT: ParamTypes:
+; CHECK-NEXT: - Index: 1
+; CHECK-NEXT: ReturnType: NORESULT
+; CHECK-NEXT: ParamTypes:
+; CHECK-NEXT: - Index: 2
+; CHECK-NEXT: ReturnType: NORESULT
+; CHECK-NEXT: ParamTypes:
+; CHECK-NEXT: - I32
+; CHECK-NEXT: - Type: FUNCTION
+; CHECK-NEXT: FunctionTypes: [ 0, 1, 1, 1, 2 ]
+; CHECK-NEXT: - Type: TABLE
+; CHECK-NEXT: Tables:
+; CHECK-NEXT: - ElemType: ANYFUNC
+; CHECK-NEXT: Limits:
+; CHECK-NEXT: Flags: [ HAS_MAX ]
+; CHECK-NEXT: Initial: 0x00000001
+; CHECK-NEXT: Maximum: 0x00000001
+; CHECK-NEXT: - Type: MEMORY
+; CHECK-NEXT: Memories:
+; CHECK-NEXT: - Initial: 0x00000002
+; CHECK-NEXT: - Type: GLOBAL
+; CHECK-NEXT: Globals:
+; CHECK-NEXT: - Index: 0
+; CHECK-NEXT: Type: I32
+; CHECK-NEXT: Mutable: true
+; CHECK-NEXT: InitExpr:
+; CHECK-NEXT: Opcode: I32_CONST
+; CHECK-NEXT: Value: 66560
+; CHECK-NEXT: - Index: 1
+; CHECK-NEXT: Type: I32
+; CHECK-NEXT: Mutable: false
+; CHECK-NEXT: InitExpr:
+; CHECK-NEXT: Opcode: I32_CONST
+; CHECK-NEXT: Value: 66560
+; CHECK-NEXT: - Index: 2
+; CHECK-NEXT: Type: I32
+; CHECK-NEXT: Mutable: false
+; CHECK-NEXT: InitExpr:
+; CHECK-NEXT: Opcode: I32_CONST
+; CHECK-NEXT: Value: 1024
+; CHECK-NEXT: - Type: EXPORT
+; CHECK-NEXT: Exports:
+; CHECK-NEXT: - Name: memory
+; CHECK-NEXT: Kind: MEMORY
+; CHECK-NEXT: Index: 0
+; CHECK-NEXT: - Name: __heap_base
+; CHECK-NEXT: Kind: GLOBAL
+; CHECK-NEXT: Index: 1
+; CHECK-NEXT: - Name: __data_end
+; CHECK-NEXT: Kind: GLOBAL
+; CHECK-NEXT: Index: 2
+; CHECK-NEXT: - Name: callWeakFuncs
+; CHECK-NEXT: Kind: FUNCTION
+; CHECK-NEXT: Index: 0
+; CHECK-NEXT: - Type: CODE
+; CHECK-NEXT: Functions:
+; CHECK-NEXT: - Index: 0
+; CHECK-NEXT: Locals:
+; CHECK-NEXT: Body: 10828080800010838080800041021084808080004180808080004180808080006A0B
+; CHECK-NEXT: - Index: 1
+; CHECK-NEXT: Locals:
+; CHECK-NEXT: Body: 0B
+; CHECK-NEXT: - Index: 2
+; CHECK-NEXT: Locals:
+; CHECK-NEXT: Body: 000B
+; CHECK-NEXT: - Index: 3
+; CHECK-NEXT: Locals:
+; CHECK-NEXT: Body: 000B
+; CHECK-NEXT: - Index: 4
+; CHECK-NEXT: Locals:
+; CHECK-NEXT: Body: 000B
+; CHECK-NEXT: - Type: CUSTOM
+; CHECK-NEXT: Name: name
+; CHECK-NEXT: FunctionNames:
+; CHECK-NEXT: - Index: 0
+; CHECK-NEXT: Name: callWeakFuncs
+; CHECK-NEXT: - Index: 1
+; CHECK-NEXT: Name: __wasm_call_ctors
+; CHECK-NEXT: - Index: 2
+; CHECK-NEXT: Name: undefined function weakFunc1
+; CHECK-NEXT: - Index: 3
+; CHECK-NEXT: Name: undefined function weakFunc2
+; CHECK-NEXT: - Index: 4
+; CHECK-NEXT: Name: undefined function weakFunc3
+; CHECK-NEXT: ...
Modified: lld/trunk/wasm/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Driver.cpp?rev=327151&r1=327150&r2=327151&view=diff
==============================================================================
--- lld/trunk/wasm/Driver.cpp (original)
+++ lld/trunk/wasm/Driver.cpp Fri Mar 9 09:06:38 2018
@@ -215,6 +215,44 @@ static StringRef getEntry(opt::InputArgL
return Arg->getValue();
}
+static const uint8_t UnreachableFn[] = {
+ 0x03 /* ULEB length */, 0x00 /* ULEB num locals */,
+ 0x00 /* opcode unreachable */, 0x0b /* opcode end */
+};
+
+// For weak undefined functions, there may be "call" instructions that reference
+// the symbol. In this case, we need to synthesise a dummy/stub function that
+// will abort at runtime, so that relocations can still provided an operand to
+// the call instruction that passes Wasm validation.
+static void handleWeakUndefines() {
+ for (Symbol *Sym : Symtab->getSymbols()) {
+ if (!Sym->isUndefined() || !Sym->isWeak())
+ continue;
+ auto *FuncSym = dyn_cast<FunctionSymbol>(Sym);
+ if (!FuncSym)
+ continue;
+
+ // It is possible for undefined functions not to have a signature (eg. if
+ // added via "--undefined"), but weak undefined ones do have a signature.
+ assert(FuncSym->getFunctionType());
+ const WasmSignature &Sig = *FuncSym->getFunctionType();
+
+ // Add a synthetic dummy for weak undefined functions. These dummies will
+ // be GC'd if not used as the target of any "call" instructions.
+ StringRef StubName =
+ Saver.save("undefined function " + toString(*Sym, false));
+ SyntheticFunction *Func = make<SyntheticFunction>(Sig, StubName);
+ Func->setBody(UnreachableFn);
+ // Ensure it compares equal to the null pointer, and so that table relocs
+ // don't pull in the stub body (only call-operand relocs should do that).
+ Func->setTableIndex(0);
+ Symtab->SyntheticFunctions.emplace_back(Func);
+ // Hide our dummy to prevent export.
+ uint32_t Flags = WASM_SYMBOL_VISIBILITY_HIDDEN;
+ replaceSymbol<DefinedFunction>(Sym, Sym->getName(), Flags, nullptr, Func);
+ }
+}
+
void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
WasmOptTable Parser;
opt::InputArgList Args = Parser.parse(ArgsArr.slice(1));
@@ -326,6 +364,10 @@ void LinkerDriver::link(ArrayRef<const c
for (InputFile *F : Files)
Symtab->addFile(F);
+ // Add synthetic dummies for weak undefined functions.
+ if (!Config->Relocatable)
+ handleWeakUndefines();
+
// Make sure we have resolved all symbols.
if (!Config->Relocatable && !Config->AllowUndefined) {
Symtab->reportRemainingUndefines();
Modified: lld/trunk/wasm/InputFiles.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/InputFiles.cpp?rev=327151&r1=327150&r2=327151&view=diff
==============================================================================
--- lld/trunk/wasm/InputFiles.cpp (original)
+++ lld/trunk/wasm/InputFiles.cpp Fri Mar 9 09:06:38 2018
@@ -65,14 +65,8 @@ uint32_t ObjFile::calcNewIndex(const Was
uint32_t ObjFile::calcNewValue(const WasmRelocation &Reloc) const {
switch (Reloc.Type) {
case R_WEBASSEMBLY_TABLE_INDEX_I32:
- case R_WEBASSEMBLY_TABLE_INDEX_SLEB: {
- // The null case is possible, if you take the address of a weak function
- // that's simply not supplied.
- FunctionSymbol *Sym = getFunctionSymbol(Reloc.Index);
- if (Sym->hasTableIndex())
- return Sym->getTableIndex();
- return 0;
- }
+ case R_WEBASSEMBLY_TABLE_INDEX_SLEB:
+ return getFunctionSymbol(Reloc.Index)->getTableIndex();
case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
case R_WEBASSEMBLY_MEMORY_ADDR_I32:
case R_WEBASSEMBLY_MEMORY_ADDR_LEB:
Modified: lld/trunk/wasm/MarkLive.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/MarkLive.cpp?rev=327151&r1=327150&r2=327151&view=diff
==============================================================================
--- lld/trunk/wasm/MarkLive.cpp (original)
+++ lld/trunk/wasm/MarkLive.cpp Fri Mar 9 09:06:38 2018
@@ -73,8 +73,25 @@ void lld::wasm::markLive() {
InputChunk *C = Q.pop_back_val();
for (const WasmRelocation Reloc : C->getRelocations()) {
- if (Reloc.Type != R_WEBASSEMBLY_TYPE_INDEX_LEB)
- Enqueue(C->File->getSymbol(Reloc.Index));
+ if (Reloc.Type == R_WEBASSEMBLY_TYPE_INDEX_LEB)
+ continue;
+ Symbol *Sym = C->File->getSymbol(Reloc.Index);
+
+ // If the function has been assigned the special index zero in the table,
+ // the relocation doesn't pull in the function body, since the function
+ // won't actually go in the table (the runtime will trap attempts to call
+ // that index, since we don't use it). A function with a table index of
+ // zero is only reachable via "call", not via "call_indirect". The stub
+ // functions used for weak-undefined symbols have this behaviour (compare
+ // equal to null pointer, only reachable via direct call).
+ if (Reloc.Type == R_WEBASSEMBLY_TABLE_INDEX_SLEB ||
+ Reloc.Type == R_WEBASSEMBLY_TABLE_INDEX_I32) {
+ FunctionSymbol *FuncSym = cast<FunctionSymbol>(Sym);
+ if (FuncSym->hasTableIndex() && FuncSym->getTableIndex() == 0)
+ continue;
+ }
+
+ Enqueue(Sym);
}
}
Modified: lld/trunk/wasm/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Symbols.cpp?rev=327151&r1=327150&r2=327151&view=diff
==============================================================================
--- lld/trunk/wasm/Symbols.cpp (original)
+++ lld/trunk/wasm/Symbols.cpp Fri Mar 9 09:06:38 2018
@@ -180,10 +180,10 @@ DefinedGlobal::DefinedGlobal(StringRef N
void LazySymbol::fetch() { cast<ArchiveFile>(File)->addMember(&ArchiveSymbol); }
-std::string lld::toString(const wasm::Symbol &Sym) {
+std::string lld::toString(const wasm::Symbol &Sym, bool QuoteDemangled) {
if (Config->Demangle)
if (Optional<std::string> S = demangleItanium(Sym.getName()))
- return "`" + *S + "'";
+ return QuoteDemangled ? ("`" + *S + "'") : *S;
return Sym.getName();
}
Modified: lld/trunk/wasm/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Symbols.h?rev=327151&r1=327150&r2=327151&view=diff
==============================================================================
--- lld/trunk/wasm/Symbols.h (original)
+++ lld/trunk/wasm/Symbols.h Fri Mar 9 09:06:38 2018
@@ -312,7 +312,7 @@ T *replaceSymbol(Symbol *S, ArgT &&... A
} // namespace wasm
// Returns a symbol name for an error message.
-std::string toString(const wasm::Symbol &Sym);
+std::string toString(const wasm::Symbol &Sym, bool QuoteDemangled = true);
std::string toString(wasm::Symbol::Kind Kind);
std::string toString(WasmSymbolType Type);
More information about the llvm-commits
mailing list