[WebAssembly] Add new relocation type for TLS data symbols

These relocations represent offsets from the __tls_base symbol.

Previously we were just using normal MEMORY_ADDR relocations and relying
on the linker to select a segment-offset rather and absolute value in
Symbol::getVirtualAddress().  Using an explicit relocation type allows
allow us to clearly distinguish absolute from relative relocations based
on the relocation information alone.

One place this is useful is being able to reject absolute relocation in
the PIC case, but still accept TLS relocations.

Differential Revision: https://reviews.llvm.org/D91276

lld/test/wasm/relocation-bad-tls.s

@@ -0,0 +1,24 @@
+# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
+# RUN: not wasm-ld %t.o -o out.wasm 2>&1 | FileCheck %s
+
+.globl _start
+_start:
+  .functype _start () -> ()
+  i32.const foo@TLSREL
+  i32.const bar@TLSREL
+  end_function
+
+.section  .data,"",@
+.globl  foo
+foo:
+  .int32  0
+  .size foo, 4
+
+.section  .bss,"",@
+.globl  bar
+bar:
+  .int32  0
+  .size bar, 4
+
+# CHECK: relocation R_WASM_MEMORY_ADDR_TLS_SLEB cannot be used against `foo` in non-TLS section: .data
+# CHECK: relocation R_WASM_MEMORY_ADDR_TLS_SLEB cannot be used against `bar` in non-TLS section: .bss

lld/test/wasm/tls.s

@@ -7,15 +7,15 @@
 tls1_addr:
   .functype tls1_addr () -> (i32)
   global.get __tls_base
-  i32.const tls1
+  i32.const tls1@TLSREL
   i32.add
   end_function
 
 .globl tls2_addr
 tls2_addr:
   .functype tls2_addr () -> (i32)
   global.get __tls_base
-  i32.const tls2
+  i32.const tls2@TLSREL
   i32.add
   end_function
 

lld/wasm/InputChunks.cpp

@@ -79,6 +79,7 @@ void InputChunk::verifyRelocTargets() const {
     case R_WASM_TABLE_INDEX_REL_SLEB:
     case R_WASM_MEMORY_ADDR_SLEB:
     case R_WASM_MEMORY_ADDR_REL_SLEB:
+    case R_WASM_MEMORY_ADDR_TLS_SLEB:
       existingValue = static_cast<uint64_t>(decodeSLEB128(loc, &bytesRead));
       break;
     case R_WASM_TABLE_INDEX_SLEB64:
@@ -158,6 +159,7 @@ void InputChunk::writeTo(uint8_t *buf) const {
     case R_WASM_TABLE_INDEX_REL_SLEB:
     case R_WASM_MEMORY_ADDR_SLEB:
     case R_WASM_MEMORY_ADDR_REL_SLEB:
+    case R_WASM_MEMORY_ADDR_TLS_SLEB:
       encodeSLEB128(static_cast<int32_t>(value), loc, 5);
       break;
     case R_WASM_TABLE_INDEX_SLEB64:

lld/wasm/InputFiles.cpp

@@ -11,6 +11,7 @@
 #include "InputChunks.h"
 #include "InputEvent.h"
 #include "InputGlobal.h"
+#include "OutputSegment.h"
 #include "SymbolTable.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Memory.h"
@@ -154,7 +155,8 @@ uint64_t ObjFile::calcExpectedValue(const WasmRelocation &reloc) const {
   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_I64:
+  case R_WASM_MEMORY_ADDR_TLS_SLEB: {
     const WasmSymbol &sym = wasmObj->syms()[reloc.Index];
     if (sym.isUndefined())
       return 0;
@@ -227,10 +229,24 @@ uint64_t ObjFile::calcNewValue(const WasmRelocation &reloc) const {
   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_I64: {
+    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 beaviour 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->name == ".tdata")
+      return D->getOutputSegmentOffset() + reloc.Addend;
+    return D->getVirtualAddress() + reloc.Addend;
+  }
+  case R_WASM_MEMORY_ADDR_TLS_SLEB:
     if (isa<UndefinedData>(sym) || sym->isUndefWeak())
       return 0;
-    return cast<DefinedData>(sym)->getVirtualAddress() + reloc.Addend;
+    // 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:

lld/wasm/OutputSections.cpp

@@ -133,13 +133,20 @@ void DataSection::finalizeContents() {
       std::count_if(segments.begin(), segments.end(),
                     [](OutputSegment *segment) { return !segment->isBss; });
 
+#ifndef NDEBUG
+  unsigned activeCount = std::count_if(
+      segments.begin(), segments.end(), [](OutputSegment *segment) {
+        return (segment->initFlags & WASM_SEGMENT_IS_PASSIVE) == 0;
+      });
+#endif
+
+  assert((!config->isPic || activeCount <= 1) &&
+         "Currenly only a single data segment is supported in PIC mode");
+
   writeUleb128(os, segmentCount, "data segment count");
   os.flush();
   bodySize = dataSectionHeader.size();
 
-  assert((!config->isPic || segments.size() <= 1) &&
-         "Currenly only a single data segment is supported in PIC mode");
-
   for (OutputSegment *segment : segments) {
     if (segment->isBss)
       continue;

lld/wasm/Relocations.cpp

@@ -9,6 +9,7 @@
 #include "Relocations.h"
 
 #include "InputChunks.h"
+#include "OutputSegment.h"
 #include "SyntheticSections.h"
 
 using namespace llvm;
@@ -88,6 +89,16 @@ void scanRelocations(InputChunk *chunk) {
       if (!isa<GlobalSymbol>(sym))
         addGOTEntry(sym);
       break;
+    case R_WASM_MEMORY_ADDR_TLS_SLEB:
+      if (auto *D = dyn_cast<DefinedData>(sym)) {
+        if (D->segment->outputSeg->name != ".tdata") {
+          error(toString(file) + ": relocation " +
+                relocTypeToString(reloc.Type) + " cannot be used against `" +
+                toString(*sym) +
+                "` in non-TLS section: " + D->segment->outputSeg->name);
+        }
+      }
+      break;
     }
 
     if (config->isPic) {

lld/wasm/Symbols.cpp

@@ -257,14 +257,8 @@ DefinedFunction::DefinedFunction(StringRef name, uint32_t flags, InputFile *f,
 
 uint64_t DefinedData::getVirtualAddress() const {
   LLVM_DEBUG(dbgs() << "getVirtualAddress: " << getName() << "\n");
-  if (segment) {
-    // For thread local data, the symbol location is relative to the start of
-    // the .tdata section, since they are used as offsets from __tls_base.
-    // Hence, we do not add in segment->outputSeg->startVA.
-    if (segment->outputSeg->name == ".tdata")
-      return segment->outputSegmentOffset + offset;
+  if (segment)
     return segment->outputSeg->startVA + segment->outputSegmentOffset + offset;
-  }
   return offset;
 }
 

lld/wasm/Writer.cpp

@@ -749,15 +749,15 @@ void Writer::assignIndexes() {
 }
 
 static StringRef getOutputDataSegmentName(StringRef name) {
-  // With PIC code we currently only support a single data segment since
-  // we only have a single __memory_base to use as our base address.
-  if (config->isPic)
-    return ".data";
   // We only support one thread-local segment, so we must merge the segments
   // despite --no-merge-data-segments.
   // We also need to merge .tbss into .tdata so they share the same offsets.
   if (name.startswith(".tdata") || name.startswith(".tbss"))
     return ".tdata";
+  // With PIC code we currently only support a single data segment since
+  // we only have a single __memory_base to use as our base address.
+  if (config->isPic)
+    return ".data";
   if (!config->mergeDataSegments)
     return name;
   if (name.startswith(".text."))
@@ -1199,10 +1199,10 @@ void Writer::run() {
 
   if (!config->relocatable) {
     // Create linker synthesized functions
-    if (config->sharedMemory)
-      createInitMemoryFunction();
     if (config->isPic)
       createApplyRelocationsFunction();
+    else if (config->sharedMemory)
+      createInitMemoryFunction();
     createCallCtorsFunction();
 
     // Create export wrappers for commands if needed.

llvm/include/llvm/BinaryFormat/WasmRelocs.def

@@ -23,3 +23,4 @@ WASM_RELOC(R_WASM_MEMORY_ADDR_REL_SLEB64, 17)
 WASM_RELOC(R_WASM_TABLE_INDEX_SLEB64,     18)
 WASM_RELOC(R_WASM_TABLE_INDEX_I64,        19)
 WASM_RELOC(R_WASM_TABLE_NUMBER_LEB,       20)
+WASM_RELOC(R_WASM_MEMORY_ADDR_TLS_SLEB,   21)

llvm/include/llvm/MC/MCExpr.h

@@ -321,8 +321,9 @@ class MCSymbolRefExpr : public MCExpr {
     VK_Hexagon_IE_GOT,
 
     VK_WASM_TYPEINDEX, // Reference to a symbol's type (signature)
-    VK_WASM_MBREL,     // Memory address relative to memory base
-    VK_WASM_TBREL,     // Table index relative to table bare
+    VK_WASM_TLSREL,    // Memory address relative to __tls_base
+    VK_WASM_MBREL,     // Memory address relative to __memory_base
+    VK_WASM_TBREL,     // Table index relative to __table_base
 
     VK_AMDGPU_GOTPCREL32_LO, // symbol@gotpcrel32@lo
     VK_AMDGPU_GOTPCREL32_HI, // symbol@gotpcrel32@hi

llvm/lib/BinaryFormat/Wasm.cpp

@@ -48,6 +48,7 @@ bool llvm::wasm::relocTypeHasAddend(uint32_t Type) {
   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_FUNCTION_OFFSET_I32:
   case R_WASM_SECTION_OFFSET_I32:
     return true;

llvm/lib/MC/MCExpr.cpp

@@ -350,6 +350,7 @@ StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
   case VK_Hexagon_IE_GOT: return "IEGOT";
   case VK_WASM_TYPEINDEX: return "TYPEINDEX";
   case VK_WASM_MBREL: return "MBREL";
+  case VK_WASM_TLSREL: return "TLSREL";
   case VK_WASM_TBREL: return "TBREL";
   case VK_AMDGPU_GOTPCREL32_LO: return "gotpcrel32@lo";
   case VK_AMDGPU_GOTPCREL32_HI: return "gotpcrel32@hi";
@@ -490,6 +491,7 @@ MCSymbolRefExpr::getVariantKindForName(StringRef Name) {
     .Case("typeindex", VK_WASM_TYPEINDEX)
     .Case("tbrel", VK_WASM_TBREL)
     .Case("mbrel", VK_WASM_MBREL)
+    .Case("tlsrel", VK_WASM_TLSREL)
     .Case("gotpcrel32@lo", VK_AMDGPU_GOTPCREL32_LO)
     .Case("gotpcrel32@hi", VK_AMDGPU_GOTPCREL32_HI)
     .Case("rel32@lo", VK_AMDGPU_REL32_LO)

llvm/lib/MC/WasmObjectWriter.cpp

@@ -576,7 +576,8 @@ WasmObjectWriter::getProvisionalValue(const WasmRelocationEntry &RelEntry,
   case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
   case wasm::R_WASM_MEMORY_ADDR_REL_SLEB64:
   case wasm::R_WASM_MEMORY_ADDR_I32:
-  case wasm::R_WASM_MEMORY_ADDR_I64: {
+  case wasm::R_WASM_MEMORY_ADDR_I64:
+  case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB: {
     // Provisional value is address of the global plus the offset
     const MCSymbolWasm *Base =
         cast<MCSymbolWasm>(Layout.getBaseSymbol(*RelEntry.Symbol));
@@ -685,6 +686,7 @@ void WasmObjectWriter::applyRelocations(
     case wasm::R_WASM_TABLE_INDEX_REL_SLEB:
     case wasm::R_WASM_MEMORY_ADDR_SLEB:
     case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
+    case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB:
       writePatchableSLEB<5>(Stream, Value, Offset);
       break;
     case wasm::R_WASM_TABLE_INDEX_SLEB64:

llvm/lib/Object/WasmObjectFile.cpp

@@ -855,6 +855,7 @@ Error WasmObjectFile::parseRelocSection(StringRef Name, ReadContext &Ctx) {
     case wasm::R_WASM_MEMORY_ADDR_SLEB:
     case wasm::R_WASM_MEMORY_ADDR_I32:
     case wasm::R_WASM_MEMORY_ADDR_REL_SLEB:
+    case wasm::R_WASM_MEMORY_ADDR_TLS_SLEB:
       if (!isValidDataSymbol(Reloc.Index))
         return make_error<GenericBinaryError>("Bad relocation data index",
                                               object_error::parse_failed);

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCTargetDesc.h

@@ -100,6 +100,11 @@ enum TOF {
   // Only applicable to data symbols.
   MO_MEMORY_BASE_REL,
 
+  // On a symbol operand this indicates that the immediate is the symbol
+  // address relative the __tls_base wasm global.
+  // Only applicable to data symbols.
+  MO_TLS_BASE_REL,
+
   // On a symbol operand this indicates that the immediate is the symbol
   // address relative the __table_base wasm global.
   // Only applicable to function symbols.

llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyWasmObjectWriter.cpp

@@ -76,6 +76,8 @@ unsigned WebAssemblyWasmObjectWriter::getRelocType(const MCValue &Target,
     case MCSymbolRefExpr::VK_WASM_TBREL:
       assert(SymA.isFunction());
       return wasm::R_WASM_TABLE_INDEX_REL_SLEB;
+    case MCSymbolRefExpr::VK_WASM_TLSREL:
+      return wasm::R_WASM_MEMORY_ADDR_TLS_SLEB;
     case MCSymbolRefExpr::VK_WASM_MBREL:
       assert(SymA.isData());
       return is64Bit() ? wasm::R_WASM_MEMORY_ADDR_REL_SLEB64

llvm/lib/Target/WebAssembly/WebAssemblyISelDAGToDAG.cpp

@@ -149,7 +149,8 @@ void WebAssemblyDAGToDAGISel::Select(SDNode *Node) {
 
     SDValue TLSBaseSym = CurDAG->getTargetExternalSymbol("__tls_base", PtrVT);
     SDValue TLSOffsetSym = CurDAG->getTargetGlobalAddress(
-        GA->getGlobal(), DL, PtrVT, GA->getOffset(), 0);
+        GA->getGlobal(), DL, PtrVT, GA->getOffset(),
+        WebAssemblyII::MO_TLS_BASE_REL);
 
     MachineSDNode *TLSBase =
         CurDAG->getMachineNode(GlobalGetIns, DL, PtrVT, TLSBaseSym);

llvm/lib/Target/WebAssembly/WebAssemblyISelLowering.h

@@ -106,6 +106,7 @@ class WebAssemblyTargetLowering final : public TargetLowering {
   SDValue LowerRETURNADDR(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerFRAMEADDR(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerGlobalAddress(SDValue Op, SelectionDAG &DAG) const;
+  SDValue LowerGlobalTLSAddress(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerExternalSymbol(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerBR_JT(SDValue Op, SelectionDAG &DAG) const;
   SDValue LowerJumpTable(SDValue Op, SelectionDAG &DAG) const;

llvm/lib/Target/WebAssembly/WebAssemblyMCInstLower.cpp

@@ -139,6 +139,9 @@ MCOperand WebAssemblyMCInstLower::lowerSymbolOperand(const MachineOperand &MO,
     case WebAssemblyII::MO_MEMORY_BASE_REL:
       Kind = MCSymbolRefExpr::VK_WASM_MBREL;
       break;
+    case WebAssemblyII::MO_TLS_BASE_REL:
+      Kind = MCSymbolRefExpr::VK_WASM_TLSREL;
+      break;
     case WebAssemblyII::MO_TABLE_BASE_REL:
       Kind = MCSymbolRefExpr::VK_WASM_TBREL;
       break;

llvm/lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

@@ -277,10 +277,9 @@ class CoalesceFeaturesAndStripAtomics final : public ModulePass {
   bool stripThreadLocals(Module &M) {
     bool Stripped = false;
     for (auto &GV : M.globals()) {
-      if (GV.getThreadLocalMode() !=
-          GlobalValue::ThreadLocalMode::NotThreadLocal) {
+      if (GV.isThreadLocal()) {
         Stripped = true;
-        GV.setThreadLocalMode(GlobalValue::ThreadLocalMode::NotThreadLocal);
+        GV.setThreadLocal(false);
       }
     }
     return Stripped;

llvm/test/CodeGen/WebAssembly/tls-general-dynamic.ll

@@ -12,7 +12,7 @@ target triple = "wasm32-unknown-unknown"
 ; CHECK-NEXT: .functype  address_of_tls () -> (i32)
 define i32 @address_of_tls() {
   ; TLS-DAG: global.get __tls_base
-  ; TLS-DAG: i32.const tls
+  ; TLS-DAG: i32.const tls@TLSREL
   ; TLS-NEXT: i32.add
   ; TLS-NEXT: return
 
@@ -25,7 +25,7 @@ define i32 @address_of_tls() {
 ; CHECK-NEXT: .functype ptr_to_tls () -> (i32)
 define i32* @ptr_to_tls() {
   ; TLS-DAG: global.get __tls_base
-  ; TLS-DAG: i32.const tls
+  ; TLS-DAG: i32.const tls@TLSREL
   ; TLS-NEXT: i32.add
   ; TLS-NEXT: return
 
@@ -38,7 +38,7 @@ define i32* @ptr_to_tls() {
 ; CHECK-NEXT: .functype tls_load () -> (i32)
 define i32 @tls_load() {
   ; TLS-DAG: global.get __tls_base
-  ; TLS-DAG: i32.const tls
+  ; TLS-DAG: i32.const tls@TLSREL
   ; TLS-NEXT: i32.add
   ; TLS-NEXT: i32.load 0
   ; TLS-NEXT: return
@@ -54,7 +54,7 @@ define i32 @tls_load() {
 ; CHECK-NEXT: .functype tls_store (i32) -> ()
 define void @tls_store(i32 %x) {
   ; TLS-DAG: global.get __tls_base
-  ; TLS-DAG: i32.const tls
+  ; TLS-DAG: i32.const tls@TLSREL
   ; TLS-NEXT: i32.add
   ; TLS-NEXT: i32.store 0
   ; TLS-NEXT: return