[lld] r358090 - [WebAssembly] Assign GOT entries symbols used in data relocations

[Sam Clegg via llvm-commits]

Author: sbc
Date: Wed Apr 10 08:06:17 2019
New Revision: 358090

URL: http://llvm.org/viewvc/llvm-project?rev=358090&view=rev
Log:
[WebAssembly] Assign GOT entries symbols used in data relocations

Differential Revision: https://reviews.llvm.org/D60492

Modified:
    lld/trunk/test/wasm/shared.ll
    lld/trunk/wasm/InputChunks.cpp
    lld/trunk/wasm/Writer.cpp

Modified: lld/trunk/test/wasm/shared.ll
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/wasm/shared.ll?rev=358090&r1=358089&r2=358090&view=diff
==============================================================================
--- lld/trunk/test/wasm/shared.ll (original)
+++ lld/trunk/test/wasm/shared.ll Wed Apr 10 08:06:17 2019
@@ -12,7 +12,7 @@ target triple = "wasm32-unknown-unknown"
 @data_addr = local_unnamed_addr global i32* @data, align 4
 @data_addr_external = local_unnamed_addr global i32* @data_external, align 4
 
-define default i32 @foo() {
+define hidden i32 @foo() {
 entry:
   ; To ensure we use __stack_pointer
   %ptr = alloca i32

Modified: lld/trunk/wasm/InputChunks.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/InputChunks.cpp?rev=358090&r1=358089&r2=358090&view=diff
==============================================================================
--- lld/trunk/wasm/InputChunks.cpp (original)
+++ lld/trunk/wasm/InputChunks.cpp Wed Apr 10 08:06:17 2019
@@ -327,17 +327,18 @@ void InputSegment::generateRelocationCod
       break;
     case R_WASM_MEMORY_ADDR_I32: {
       Symbol *Sym = File->getSymbol(Rel);
-      if (Sym->isUndefined()) {
-        // Undefined addresses are accessed via imported GOT globals
-        writeU8(OS, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
-        writeUleb128(OS, Sym->getGOTIndex(), "global index");
-      } else {
-        // Defined global data is accessed via known offset from __memory_base
+      if (Sym->isLocal() || Sym->isHidden()) {
+        // Hidden/Local data symbols are accessed via known offset from
+        // __memory_base
         writeU8(OS, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
         writeUleb128(OS, WasmSym::MemoryBase->getGlobalIndex(), "memory_base");
         writeU8(OS, WASM_OPCODE_I32_CONST, "CONST");
         writeSleb128(OS, File->calcNewValue(Rel), "new memory offset");
         writeU8(OS, WASM_OPCODE_I32_ADD, "ADD");
+      } else {
+        // Default data symbols are accessed via imported GOT globals
+        writeU8(OS, WASM_OPCODE_GLOBAL_GET, "GLOBAL_GET");
+        writeUleb128(OS, Sym->getGOTIndex(), "global index");
       }
       break;
     }

Modified: lld/trunk/wasm/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/wasm/Writer.cpp?rev=358090&r1=358089&r2=358090&view=diff
==============================================================================
--- lld/trunk/wasm/Writer.cpp (original)
+++ lld/trunk/wasm/Writer.cpp Wed Apr 10 08:06:17 2019
@@ -1162,22 +1162,33 @@ void Writer::processRelocations(InputChu
     }
 
     if (Config->Pic) {
-      // Certain relocation types can't be used when building PIC output, since
-      // they would require absolute symbol addresses at link time.
       switch (Reloc.Type) {
       case R_WASM_TABLE_INDEX_SLEB:
       case R_WASM_MEMORY_ADDR_SLEB:
       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: {
+        // 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;
+      }
       }
     }
   }
-
 }
 
 void Writer::assignIndexes() {