[PATCH] D64280: [lld][WebAssembly] Report undefined data relocations earlier

[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.

See https://github.com/emscripten-core/emscripten/issues/8930.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D64280

Files:
  lld/wasm/InputFiles.cpp
  lld/wasm/Relocations.cpp


Index: lld/wasm/Relocations.cpp
===================================================================
--- lld/wasm/Relocations.cpp
+++ lld/wasm/Relocations.cpp
@@ -50,16 +50,16 @@
       if (!isa<GlobalSymbol>(Sym))
         Out.ImportSec->addGOTEntry(Sym);
       break;
-    case R_WASM_MEMORY_ADDR_SLEB:
-    case R_WASM_MEMORY_ADDR_LEB:
-    case R_WASM_MEMORY_ADDR_REL_SLEB:
-      if (!Config->Relocatable && Sym->isUndefined() && !Sym->isWeak()) {
+    }
+
+    // Handle undefined data symbols.
+    // For non-weak symbols this is normally an error except in the PIC case
+    // where we can generate runtime relocations for R_WASM_MEMORY_ADDR_I32.
+    if (isa<UndefinedData>(Sym) && !Config->Relocatable && !Sym->isWeak())
+      if (!(Config->Pic && Reloc.Type == R_WASM_MEMORY_ADDR_I32))
         error(toString(File) + ": cannot resolve relocation of type " +
               relocTypeToString(Reloc.Type) +
               " against undefined (non-weak) data symbol: " + toString(*Sym));
-      }
-      break;
-    }
 
     if (Config->Pic) {
       switch (Reloc.Type) {
Index: lld/wasm/InputFiles.cpp
===================================================================
--- lld/wasm/InputFiles.cpp
+++ lld/wasm/InputFiles.cpp
@@ -161,21 +161,11 @@
     if ((isa<FunctionSymbol>(Sym) || isa<DataSymbol>(Sym)) && !Sym->isLive())
       return 0;
 
-    // Special handling for undefined data symbols.  Most relocations against
-    // such symbols cannot be resolved.
-    if (isa<DataSymbol>(Sym) && Sym->isUndefined()) {
-      if (Sym->isWeak() || Config->Relocatable)
-        return 0;
-      // R_WASM_MEMORY_ADDR_I32 relocations in PIC code are turned into runtime
-      // fixups in __wasm_apply_relocs
-      if (Config->Pic && Reloc.Type == R_WASM_MEMORY_ADDR_I32)
-        return 0;
-      if (Reloc.Type != R_WASM_GLOBAL_INDEX_LEB) {
-        llvm_unreachable(
-          ("invalid relocation against undefined data symbol: " + toString(*Sym))
-              .c_str());
-      }
-    }
+    // Special handling for undefined data symbols.  For weak symbols or for
+    // data relocations in PIC mode writing zero is the correct behaviour.  For
+    // other cases, an error will have been reported during scanRelocations.
+    if (isa<DataSymbol>(Sym) && Sym->isUndefined())
+      return 0;
   }
 
   switch (Reloc.Type) {


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