[PATCH] D59337: [WebAssembly] Error on R_WASM_MEMORY_ADDR relocations against undefined data symbols.

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
Herald added subscribers: llvm-commits, sunfish, aheejin, jgravelle-google, dschuff.
Herald added a project: LLVM.

For these types of relocations an absolute memory address is
required which is not possible for undefined data symbols.  For symbols
that can be undefined at link time (i.e. external data symbols in
shared libraries) a different type of relocation (i.e. via a GOT) will
be needed.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D59337

Files:
  lld/test/wasm/shared.ll
  lld/wasm/Writer.cpp


Index: lld/wasm/Writer.cpp
===================================================================
--- lld/wasm/Writer.cpp
+++ lld/wasm/Writer.cpp
@@ -1041,17 +1041,32 @@
     ObjFile *File = Chunk->File;
     ArrayRef<WasmSignature> Types = File->getWasmObj()->types();
     for (const WasmRelocation &Reloc : Chunk->getRelocations()) {
-      if (Reloc.Type == R_WASM_TABLE_INDEX_I32 ||
-          Reloc.Type == R_WASM_TABLE_INDEX_SLEB) {
+      switch (Reloc.Type) {
+      case R_WASM_TABLE_INDEX_I32:
+      case R_WASM_TABLE_INDEX_SLEB: {
         FunctionSymbol *Sym = File->getFunctionSymbol(Reloc.Index);
         if (Sym->hasTableIndex() || !Sym->hasFunctionIndex())
           continue;
         Sym->setTableIndex(TableIndex++);
         IndirectFunctions.emplace_back(Sym);
-      } else if (Reloc.Type == R_WASM_TYPE_INDEX_LEB) {
+        break;
+      }
+      case R_WASM_TYPE_INDEX_LEB:
         // Mark target type as live
         File->TypeMap[Reloc.Index] = registerType(Types[Reloc.Index]);
         File->TypeIsUsed[Reloc.Index] = true;
+        break;
+      case R_WASM_MEMORY_ADDR_SLEB:
+      case R_WASM_MEMORY_ADDR_I32:
+      case R_WASM_MEMORY_ADDR_LEB: {
+        DataSymbol* DataSym = File->getDataSymbol(Reloc.Index);
+        if (!Config->Relocatable && !isa<DefinedData>(DataSym) && !DataSym->isWeak())
+          error(File->getName() +
+                ": relocation of type R_WASM_MEMORY_* against undefined data "
+                "symbol: " +
+                DataSym->getName());
+        break;
+      }
       }
     }
   };
Index: lld/test/wasm/shared.ll
===================================================================
--- lld/test/wasm/shared.ll
+++ lld/test/wasm/shared.ll
@@ -13,10 +13,12 @@
   ; To ensure we use __stack_pointer
   %ptr = alloca i32
   %0 = load i32, i32* @data, align 4
-  %1 = load i32, i32* @data_external, align 4
-  %2 = load i32 ()*, i32 ()** @indirect_func, align 4
-  call i32 %2()
-  ret i32 %1
+  ; TODO(sbc): Re-enable once the codegen supports generating the correct
+  ; relocation type when referencing external data in shared libraries.
+  ; %1 = load i32, i32* @data_external, align 4
+  %1 = load i32 ()*, i32 ()** @indirect_func, align 4
+  call i32 %1()
+  ret i32 %0
 }
 
 declare void @func_external()
@@ -29,7 +31,7 @@
 ; CHECK:      Sections:
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            dylink
-; CHECK-NEXT:     MemorySize:      8
+; CHECK-NEXT:     MemorySize:      12
 ; CHECK-NEXT:     MemoryAlignment: 2
 ; CHECK-NEXT:     TableSize:       2
 ; CHECK-NEXT:     TableAlignment:  0
@@ -60,11 +62,11 @@
 ; CHECK-NEXT:         Kind:            GLOBAL
 ; CHECK-NEXT:         GlobalType:      I32
 ; CHECK-NEXT:         GlobalMutable:   false
-; CHECK-NEXT:       - Module:          env
-; CHECK-NEXT:         Field:           data_external
-; CHECK-NEXT:         Kind:            GLOBAL
-; CHECK-NEXT:         GlobalType:      I32
-; CHECK-NEXT:         GlobalMutable:   true
+; XCHECK-NEXT:       - Module:          env
+; XCHECK-NEXT:         Field:           data_external
+; XCHECK-NEXT:         Kind:            GLOBAL
+; XCHECK-NEXT:         GlobalType:      I32
+; XCHECK-NEXT:         GlobalMutable:   true
 ; CHECK-NEXT:       - Module:          env
 ; CHECK-NEXT:         Field:           func_external
 ; CHECK-NEXT:         Kind:            FUNCTION
@@ -88,4 +90,4 @@
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          GLOBAL_GET
 ; CHECK-NEXT:           Index:           1
-; CHECK-NEXT:         Content:         '0000000001000000'
+; CHECK-NEXT:         Content:         '020000000000000001000000'


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