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[WebAssembly] Don't generate unused table entries. 

When generating PIC output only relocations of type
R_WASM_TABLE_INDEX_REL_SLEB should generate table entries.

R_WASM_TABLE_INDEX_I32 get resolved at runtime via the auto-generated
__wasm_apply_relocs functions.

R_WASM_TABLE_INDEX_SLEB are not allowed in PIC code.

Differential Revision: https://reviews.llvm.org/D61539

llvm-svn: 360165
This commit is contained in:
Sam Clegg 2019-05-07 15:46:30 +00:00
parent 3044ac058b
commit b33fdb7768
4 changed files with 28 additions and 26 deletions
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2
lld/test/wasm/pie.ll
View File

@ -38,7 +38,7 @@ define void @_start() {
; CHECK-NEXT: Table:
; CHECK-NEXT: ElemType: FUNCREF
; CHECK-NEXT: Limits:
; CHECK-NEXT: Initial: 0x00000001
; CHECK-NEXT: Initial: 0x00000000
; CHECK-NEXT: - Module: env
; CHECK-NEXT: Field: __memory_base
; CHECK-NEXT: Kind: GLOBAL

10
lld/test/wasm/shared.ll
View File

@ -54,7 +54,7 @@ declare void @func_external()
; CHECK-NEXT: Name: dylink
; CHECK-NEXT: MemorySize: 24
; CHECK-NEXT: MemoryAlignment: 2
; CHECK-NEXT: TableSize: 3
; CHECK-NEXT: TableSize: 1
; CHECK-NEXT: TableAlignment: 0
; CHECK-NEXT: Needed: []
; CHECK-NEXT: - Type: TYPE
@ -74,7 +74,7 @@ declare void @func_external()
; CHECK-NEXT: Table:
; CHECK-NEXT: ElemType: FUNCREF
; CHECK-NEXT: Limits:
; CHECK-NEXT: Initial: 0x00000003
; CHECK-NEXT: Initial: 0x00000001
; CHECK-NEXT: - Module: env
; CHECK-NEXT: Field: __stack_pointer
; CHECK-NEXT: Kind: GLOBAL
@ -124,7 +124,7 @@ declare void @func_external()
; CHECK-NEXT: - Offset:
; CHECK-NEXT: Opcode: GLOBAL_GET
; CHECK-NEXT: Index: 2
; CHECK-NEXT: Functions: [ 5, 3, 0 ]
; CHECK-NEXT: Functions: [ 5 ]
; check the generated code in __wasm_call_ctors and __wasm_apply_relocs functions
; TODO(sbc): Disassemble and verify instructions.
@ -136,7 +136,7 @@ declare void @func_external()
; CHECK-NEXT: Body: 10020B
; CHECK-NEXT: - Index: 2
; CHECK-NEXT: Locals: []
; CHECK-NEXT: Body: 230141046A230241016A360200230141086A23043602002301410C6A230141006A360200230141106A2303360200230141146A230541046A3602000B
; CHECK-NEXT: Body: 230141046A230241006A360200230141086A23043602002301410C6A230141006A360200230141106A2303360200230141146A230541046A3602000B
; check the data segment initialized with __memory_base global as offset
@ -147,4 +147,4 @@ declare void @func_external()
; CHECK-NEXT: Offset:
; CHECK-NEXT: Opcode: GLOBAL_GET
; CHECK-NEXT: Index: 1
; CHECK-NEXT: Content: '020000000100000002000000000000000000000000000000'
; CHECK-NEXT: Content: '020000000000000000000000000000000000000000000000'

2
lld/wasm/InputFiles.cpp
View File

@ -171,6 +171,8 @@ uint32_t ObjFile::calcNewValue(const WasmRelocation &Reloc) const {
case R_WASM_TABLE_INDEX_I32:
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_TABLE_INDEX_REL_SLEB:
if (Config->Pic && !getFunctionSymbol(Reloc.Index)->hasTableIndex())
return 0;
return getFunctionSymbol(Reloc.Index)->getTableIndex();
case R_WASM_MEMORY_ADDR_SLEB:
case R_WASM_MEMORY_ADDR_I32:

40
lld/wasm/Writer.cpp
View File

@ -1148,35 +1148,40 @@ void Writer::processRelocations(InputChunk *Chunk) {
ObjFile *File = Chunk->File;
ArrayRef<WasmSignature> Types = File->getWasmObj()->types();
for (const WasmRelocation &Reloc : Chunk->getRelocations()) {
if (Reloc.Type == R_WASM_TYPE_INDEX_LEB) {
// Mark target type as live
File->TypeMap[Reloc.Index] = registerType(Types[Reloc.Index]);
File->TypeIsUsed[Reloc.Index] = true;
continue;
}
// Other relocation types all have a corresponding symbol
auto *Sym = File->getSymbols()[Reloc.Index];
switch (Reloc.Type) {
case R_WASM_TABLE_INDEX_I32:
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_TABLE_INDEX_REL_SLEB: {
FunctionSymbol *Sym = File->getFunctionSymbol(Reloc.Index);
if (Sym->hasTableIndex() || !Sym->hasFunctionIndex())
continue;
Sym->setTableIndex(TableBase + IndirectFunctions.size());
IndirectFunctions.emplace_back(Sym);
if (Config->Pic && Reloc.Type != R_WASM_TABLE_INDEX_REL_SLEB)
break;
auto *F = cast<FunctionSymbol>(Sym);
if (F->hasTableIndex() || !F->hasFunctionIndex())
break;
F->setTableIndex(TableBase + IndirectFunctions.size());
IndirectFunctions.emplace_back(F);
break;
}
case R_WASM_TYPE_INDEX_LEB:
// Mark target type as live
File->TypeMap[Reloc.Index] = registerType(Types[Reloc.Index]);
File->TypeIsUsed[Reloc.Index] = true;
break;
case R_WASM_GLOBAL_INDEX_LEB: {
auto* Sym = File->getSymbols()[Reloc.Index];
case R_WASM_GLOBAL_INDEX_LEB:
if (!isa<GlobalSymbol>(Sym) && !Sym->isInGOT()) {
Sym->setGOTIndex(NumImportedGlobals++);
GOTSymbols.push_back(Sym);
}
break;
}
case R_WASM_MEMORY_ADDR_SLEB:
case R_WASM_MEMORY_ADDR_LEB:
case R_WASM_MEMORY_ADDR_REL_SLEB: {
case R_WASM_MEMORY_ADDR_REL_SLEB:
if (!Config->Relocatable) {
auto* Sym = File->getSymbols()[Reloc.Index];
if (Sym->isUndefined() && !Sym->isWeak()) {
error(toString(File) + ": cannot resolve relocation of type " +
relocTypeToString(Reloc.Type) +
@ -1185,34 +1190,29 @@ void Writer::processRelocations(InputChunk *Chunk) {
}
break;
}
}
if (Config->Pic) {
switch (Reloc.Type) {
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_MEMORY_ADDR_SLEB:
case R_WASM_MEMORY_ADDR_LEB: {
case R_WASM_MEMORY_ADDR_LEB:
// Certain relocation types can't be used when building PIC output, since
// they would require absolute symbol addresses at link time.
Symbol *Sym = File->getSymbols()[Reloc.Index];
error(toString(File) + ": relocation " +
relocTypeToString(Reloc.Type) + " cannot be used againt symbol " +
toString(*Sym) + "; recompile with -fPIC");
break;
}
case R_WASM_TABLE_INDEX_I32:
case R_WASM_MEMORY_ADDR_I32: {
case R_WASM_MEMORY_ADDR_I32:
// These relocation types are only present in the data section and
// will be converted into code by `generateRelocationCode`. This code
// requires the symbols to have GOT entires.
auto* Sym = File->getSymbols()[Reloc.Index];
if (!Sym->isHidden() && !Sym->isLocal() && !Sym->isInGOT()) {
Sym->setGOTIndex(NumImportedGlobals++);
GOTSymbols.push_back(Sym);
}
break;
}
}
}
}
}