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[WebAssembly] Verify contents of relocation target before writing it

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Verify that the location where a relocation is about the be
applied contains the expected existing value.

This is essentially a sanity check to catch bugs in the compiler
and the linker.

Differential Revision: https://reviews.llvm.org/D44349

llvm-svn: 327325
This commit is contained in:
Sam Clegg
2018-03-12 19:54:26 +00:00
parent b672f7a251
commit dbd33b80b7
3 changed files with 61 additions and 0 deletions
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47
lld/wasm/InputFiles.cpp
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@@ -60,6 +60,37 @@ uint32_t ObjFile::calcNewIndex(const WasmRelocation &Reloc) const {
return Symbols[Reloc.Index]->getOutputSymbolIndex();
}
// Calculate the value we expect to find at the relocation location.
// This is used as a sanity check before applying a relocation to a given
// location. It is useful for catching bugs in the compiler and linker.
uint32_t ObjFile::calcExpectedValue(const WasmRelocation &Reloc) const {
switch (Reloc.Type) {
case R_WEBASSEMBLY_TABLE_INDEX_I32:
case R_WEBASSEMBLY_TABLE_INDEX_SLEB: {
const WasmSymbol& Sym = WasmObj->syms()[Reloc.Index];
return TableEntries[Sym.Info.ElementIndex];
}
case R_WEBASSEMBLY_MEMORY_ADDR_SLEB:
case R_WEBASSEMBLY_MEMORY_ADDR_I32:
case R_WEBASSEMBLY_MEMORY_ADDR_LEB: {
const WasmSymbol& Sym = WasmObj->syms()[Reloc.Index];
if (Sym.isUndefined())
return 0;
const WasmSegment& Segment = WasmObj->dataSegments()[Sym.Info.DataRef.Segment];
return Segment.Data.Offset.Value.Int32 + Sym.Info.DataRef.Offset;
}
case R_WEBASSEMBLY_TYPE_INDEX_LEB:
return Reloc.Index;
case R_WEBASSEMBLY_FUNCTION_INDEX_LEB:
case R_WEBASSEMBLY_GLOBAL_INDEX_LEB: {
const WasmSymbol& Sym = WasmObj->syms()[Reloc.Index];
return Sym.Info.ElementIndex;
}
default:
llvm_unreachable("unknown relocation type");
}
}
// Translate from the relocation's index into the final linked output value.
uint32_t ObjFile::calcNewValue(const WasmRelocation &Reloc) const {
switch (Reloc.Type) {
@@ -97,6 +128,22 @@ void ObjFile::parse() {
Bin.release();
WasmObj.reset(Obj);
// Build up a map of function indices to table indices for use when
// verifying the existing table index relocations
uint32_t TotalFunctions =
WasmObj->getNumImportedFunctions() + WasmObj->functions().size();
TableEntries.resize(TotalFunctions);
for (const WasmElemSegment &Seg : WasmObj->elements()) {
if (Seg.Offset.Opcode != WASM_OPCODE_I32_CONST)
fatal(toString(this) + ": invalid table elements");
uint32_t Offset = Seg.Offset.Value.Int32;
for (uint32_t Index = 0; Index < Seg.Functions.size(); Index++) {
uint32_t FunctionIndex = Seg.Functions[Index];
TableEntries[FunctionIndex] = Offset + Index;
}
}
// Find the code and data sections. Wasm objects can have at most one code
// and one data section.
for (const SectionRef &Sec : WasmObj->sections()) {