[WebAssembly] Use __stack_pointer global when writing wasm binary

This ensures that symbolic relocations are generated for stack
pointer manipulations.

These relocations are of type R_WEBASSEMBLY_GLOBAL_INDEX_LEB.
This change also adds support for reading relocations of this
type in WasmObjectFile.cpp.

Since its a globally imported symbol this does mean that
the get_global/set_global instruction won't be valid until
the objects are linked that global used in no longer an
imported global.

Differential Revision: https://reviews.llvm.org/D34172

llvm-svn: 305616

1 files changed, 7 insertions, 11 deletions

diff --git a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
index c56c591def3..3e3b52fca56 100644
--- a/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
+++ b/llvm/lib/Target/WebAssembly/MCTargetDesc/WebAssemblyMCCodeEmitter.cpp
@@ -36,7 +36,6 @@ STATISTIC(MCNumFixups, "Number of MC fixups created.");
 namespace {
 class WebAssemblyMCCodeEmitter final : public MCCodeEmitter {
   const MCInstrInfo &MCII;
-  MCContext &Ctx;
 
   // Implementation generated by tablegen.
   uint64_t getBinaryCodeForInstr(const MCInst &MI,
@@ -48,14 +47,12 @@ class WebAssemblyMCCodeEmitter final : public MCCodeEmitter {
                          const MCSubtargetInfo &STI) const override;
 
 public:
-  WebAssemblyMCCodeEmitter(const MCInstrInfo &mcii, MCContext &ctx)
-      : MCII(mcii), Ctx(ctx) {}
+  WebAssemblyMCCodeEmitter(const MCInstrInfo &mcii) : MCII(mcii) {}
 };
 } // end anonymous namespace
 
-MCCodeEmitter *llvm::createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII,
-                                                    MCContext &Ctx) {
-  return new WebAssemblyMCCodeEmitter(MCII, Ctx);
+MCCodeEmitter *llvm::createWebAssemblyMCCodeEmitter(const MCInstrInfo &MCII) {
+  return new WebAssemblyMCCodeEmitter(MCII);
 }
 
 void WebAssemblyMCCodeEmitter::encodeInstruction(
@@ -89,11 +86,7 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
         } else if (Info.OperandType == WebAssembly::OPERAND_I64IMM) {
           encodeSLEB128(int64_t(MO.getImm()), OS);
         } else if (Info.OperandType == WebAssembly::OPERAND_GLOBAL) {
-          Fixups.push_back(MCFixup::create(
-              OS.tell() - Start, MCConstantExpr::create(MO.getImm(), Ctx),
-              MCFixupKind(WebAssembly::fixup_code_global_index), MI.getLoc()));
-          ++MCNumFixups;
-          encodeULEB128(uint64_t(MO.getImm()), OS);
+          llvm_unreachable("wasm globals should only be accessed symbolicly");
         } else if (Info.OperandType == WebAssembly::OPERAND_SIGNATURE) {
           encodeSLEB128(int64_t(MO.getImm()), OS);
         } else {
@@ -135,6 +128,9 @@ void WebAssemblyMCCodeEmitter::encodeInstruction(
                  Info.OperandType == WebAssembly::OPERAND_TYPEINDEX) {
         FixupKind = MCFixupKind(WebAssembly::fixup_code_uleb128_i32);
         PaddedSize = 5;
+      } else if (Info.OperandType == WebAssembly::OPERAND_GLOBAL) {
+        FixupKind = MCFixupKind(WebAssembly::fixup_code_global_index);
+        PaddedSize = 5;
       } else {
         llvm_unreachable("unexpected symbolic operand kind");
       }