[WebAssembly] De-dup indirect function table.
Create the indirect function table based on symbols rather
than just duplicating the input entries. This has the
effect of de-duplicating the table.
This is a followup to the equivalent change made for globals:
https://reviews.llvm.org/D40859
Partially based on a patch by Nicholas Wilson:
https://reviews.llvm.org/D40845
Differential Revision: https://reviews.llvm.org/D40989
llvm-svn: 320428
diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
index 7af5df3..4d9d923 100644
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -103,10 +103,7 @@
uint64_t FileSize = 0;
uint32_t DataSize = 0;
uint32_t NumFunctions = 0;
- uint32_t NumGlobals = 0;
uint32_t NumMemoryPages = 0;
- uint32_t NumTableElems = 0;
- uint32_t NumElements = 0;
uint32_t InitialTableOffset = 0;
std::vector<const WasmSignature *> Types;
@@ -114,6 +111,7 @@
std::vector<const Symbol *> FunctionImports;
std::vector<const Symbol *> GlobalImports;
std::vector<const Symbol *> DefinedGlobals;
+ std::vector<const Symbol *> IndirectFunctions;
// Elements that are used to construct the final output
std::string Header;
@@ -236,14 +234,24 @@
}
void Writer::createTableSection() {
+ // Always output a table section, even if there are no indirect calls.
+ // There are two reasons for this:
+ // 1. For executables it is useful to have an empty table slot at 0
+ // which can be filled with a null function call handler.
+ // 2. If we don't do this, any program that contains a call_indirect but
+ // no address-taken function will fail at validation time since it is
+ // a validation error to include a call_indirect instruction if there
+ // is not table.
+ uint32_t TableSize = InitialTableOffset + IndirectFunctions.size();
+
SyntheticSection *Section = createSyntheticSection(WASM_SEC_TABLE);
raw_ostream &OS = Section->getStream();
writeUleb128(OS, 1, "table count");
writeSleb128(OS, WASM_TYPE_ANYFUNC, "table type");
writeUleb128(OS, WASM_LIMITS_FLAG_HAS_MAX, "table flags");
- writeUleb128(OS, NumTableElems, "table initial size");
- writeUleb128(OS, NumTableElems, "table max size");
+ writeUleb128(OS, TableSize, "table initial size");
+ writeUleb128(OS, TableSize, "table max size");
}
void Writer::createExportSection() {
@@ -309,7 +317,7 @@
void Writer::createStartSection() {}
void Writer::createElemSection() {
- if (!NumElements)
+ if (IndirectFunctions.empty())
return;
SyntheticSection *Section = createSyntheticSection(WASM_SEC_ELEM);
@@ -321,13 +329,14 @@
InitExpr.Opcode = WASM_OPCODE_I32_CONST;
InitExpr.Value.Int32 = InitialTableOffset;
writeInitExpr(OS, InitExpr);
- writeUleb128(OS, NumElements, "elem count");
+ writeUleb128(OS, IndirectFunctions.size(), "elem count");
- for (ObjFile *File : Symtab->ObjectFiles)
- for (const WasmElemSegment &Segment : File->getWasmObj()->elements())
- for (uint64_t FunctionIndex : Segment.Functions)
- writeUleb128(OS, File->relocateFunctionIndex(FunctionIndex),
- "function index");
+ uint32_t TableIndex = InitialTableOffset;
+ for (const Symbol *Sym : IndirectFunctions) {
+ assert(Sym->getTableIndex() == TableIndex);
+ writeUleb128(OS, Sym->getOutputIndex(), "function index");
+ ++TableIndex;
+ }
}
void Writer::createCodeSection() {
@@ -526,8 +535,6 @@
}
void Writer::calculateOffsets() {
- NumTableElems = InitialTableOffset;
-
for (ObjFile *File : Symtab->ObjectFiles) {
const WasmObjectFile *WasmFile = File->getWasmObj();
@@ -537,34 +544,8 @@
NumFunctions += WasmFile->functions().size();
// Memory
- if (WasmFile->memories().size()) {
- if (WasmFile->memories().size() > 1) {
- fatal(File->getName() + ": contains more than one memory");
- }
- }
-
- // Table
- uint32_t TableCount = WasmFile->tables().size();
- if (TableCount) {
- if (TableCount > 1)
- fatal(File->getName() + ": contains more than one table");
- File->TableIndexOffset = NumTableElems;
- NumTableElems += WasmFile->tables()[0].Limits.Initial;
- }
-
- // Elem
- uint32_t SegmentCount = WasmFile->elements().size();
- if (SegmentCount) {
- if (SegmentCount > 1)
- fatal(File->getName() + ": contains more than element segment");
-
- const WasmElemSegment &Segment = WasmFile->elements()[0];
- if (Segment.TableIndex != 0)
- fatal(File->getName() + ": unsupported table index");
- if (Segment.Offset.Value.Int32 != 0)
- fatal(File->getName() + ": unsupported segment offset");
- NumElements += Segment.Functions.size();
- }
+ if (WasmFile->memories().size() > 1)
+ fatal(File->getName() + ": contains more than one memory");
}
}
@@ -611,8 +592,11 @@
if (Config->EmitRelocs)
DefinedGlobals.reserve(Symtab->getSymbols().size());
+ uint32_t TableIndex = InitialTableOffset;
+
for (ObjFile *File : Symtab->ObjectFiles) {
DEBUG(dbgs() << "assignSymbolIndexes: " << File->getName() << "\n");
+
for (Symbol *Sym : File->getSymbols()) {
// Assign indexes for symbols defined with this file.
if (!Sym->isDefined() || File != Sym->getFile())
@@ -626,6 +610,13 @@
Sym->setOutputIndex(GlobalIndex++);
}
}
+
+ for (Symbol *Sym : File->getTableSymbols()) {
+ if (!Sym->hasTableIndex()) {
+ Sym->setTableIndex(TableIndex++);
+ IndirectFunctions.emplace_back(Sym);
+ }
+ }
}
}
@@ -679,12 +670,12 @@
calculateOffsets();
if (errorHandler().Verbose) {
- log("NumFunctions : " + Twine(NumFunctions));
- log("NumGlobals : " + Twine(NumGlobals));
- log("NumImports : " +
+ log("Defined Functions: " + Twine(NumFunctions));
+ log("Defined Globals : " + Twine(DefinedGlobals.size()));
+ log("Function Imports : " + Twine(FunctionImports.size()));
+ log("Global Imports : " + Twine(GlobalImports.size()));
+ log("Total Imports : " +
Twine(FunctionImports.size() + GlobalImports.size()));
- log("FunctionImports : " + Twine(FunctionImports.size()));
- log("GlobalImports : " + Twine(GlobalImports.size()));
for (ObjFile *File : Symtab->ObjectFiles)
File->dumpInfo();
}