[lld][WebAssembly] Handle TLS variables in Symbol::getVA. NFC

[sbc100]

Summary

In the shared memory case we can always assume that TLS addresses
are relative to __tls_base. In the non-shared memory case TLS
variables are absolute, just like normal data addresses.

This simplifies the code in calcNewValue so that TLS relocations
no longer need special handling.

[sbc100]

lld/wasm/InputFiles.cpp

182

This is taken care of now simply my marking the symbols as TLS which happens elsewhere in this file:

// Older object files did not include WASM_SEG_FLAG_TLS and instead                  
// relied on the naming convention.  To maintain compat with such objects    
// we still imply the TLS flag based on the name of the segment.             
if (!seg->isTLS() &&                                                         
    (seg->name.startswith(".tdata") || seg->name.startswith(".tbss"))) {     
  seg->flags |= WASM_SEG_FLAG_TLS;                                           
  seg->implicitTLS = true;                                                   
}

[sbc100]

• comment

[sbc100]

• comment

lld/wasm/InputFiles.cpp

uint64_t ObjFile::calcNewValue(const WasmRelocation &reloc, uint64_t tombstone,
   case R_WASM_MEMORY_ADDR_LEB:
   case R_WASM_MEMORY_ADDR_LEB64:
   case R_WASM_MEMORY_ADDR_SLEB:
   case R_WASM_MEMORY_ADDR_SLEB64:
   case R_WASM_MEMORY_ADDR_REL_SLEB:
   case R_WASM_MEMORY_ADDR_REL_SLEB64:
   case R_WASM_MEMORY_ADDR_I32:
   case R_WASM_MEMORY_ADDR_I64:
+  case R_WASM_MEMORY_ADDR_TLS_SLEB:
+  case R_WASM_MEMORY_ADDR_TLS_SLEB64:
   case R_WASM_MEMORY_ADDR_LOCREL_I32: {
     if (isa<UndefinedData>(sym) || sym->isUndefWeak())
       return 0;
     auto D = cast<DefinedData>(sym);
-    // Treat non-TLS relocation against symbols that live in the TLS segment
-    // like TLS relocations.  This behaviour exists to support older object
-    // files created before we introduced TLS relocations.
-    // TODO(sbc): Remove this legacy behaviour one day.  This will break
-    // backward compat with old object files built with `-fPIC`.
-    if (D->segment && D->segment->outputSeg->isTLS())
-      return D->getOutputSegmentOffset() + reloc.Addend;
-
     uint64_t value = D->getVA() + reloc.Addend;
     if (reloc.Type == R_WASM_MEMORY_ADDR_LOCREL_I32) {
       const auto *segment = cast<InputSegment>(chunk);
       uint64_t p = segment->outputSeg->startVA + segment->outputSegmentOffset +
                    reloc.Offset - segment->getInputSectionOffset();
       value -= p;
     }
     return value;
   }
-  case R_WASM_MEMORY_ADDR_TLS_SLEB:
-  case R_WASM_MEMORY_ADDR_TLS_SLEB64:
-    if (isa<UndefinedData>(sym) || sym->isUndefWeak())
-      return 0;
-    // TLS relocations are relative to the start of the TLS output segment
-    return cast<DefinedData>(sym)->getOutputSegmentOffset() + reloc.Addend;
   case R_WASM_TYPE_INDEX_LEB:
     return typeMap[reloc.Index];
   case R_WASM_FUNCTION_INDEX_LEB:
     return getFunctionSymbol(reloc.Index)->getFunctionIndex();
   case R_WASM_GLOBAL_INDEX_LEB:
   case R_WASM_GLOBAL_INDEX_I32:
     if (auto gs = dyn_cast<GlobalSymbol>(sym))
       return gs->getGlobalIndex();

lld/wasm/Symbols.cpp

: FunctionSymbol(name, DefinedFunctionKind, flags, f,
       function(function) {}
 
 uint32_t DefinedFunction::getExportedFunctionIndex() const {
   return function->getFunctionIndex();
 }
 
 uint64_t DefinedData::getVA() const {
   LLVM_DEBUG(dbgs() << "getVA: " << getName() << "\n");
+  // In the shared memory case, TLS symbols are relative to the start of the TLS
+  // output segment (__tls_base).  When building without shared memory, TLS
+  // symbols absolute, just like non-TLS.
+  if (isTLS() && config->sharedMemory)
+    return getOutputSegmentOffset() + value;
   if (segment)
     return segment->getVA(value);
   return value;
 }
 
 void DefinedData::setVA(uint64_t value_) {
   LLVM_DEBUG(dbgs() << "setVA " << name << " -> " << value_ << "\n");
   assert(!segment);