[PATCH] D148747: [WebAssebmly][MC] Ingore undefined init functions when writing object file

[Sam Clegg via Phabricator via llvm-commits]

sbc100 created this revision.
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This is really a workaround for #62243.  Ideally we would ensure that
llvm never emits object files that contain undefined init function, but
I have yet to find a small enough repro case to fully understand how the
such a things is possible.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D148747

Files:
  lld/wasm/LTO.cpp
  lld/wasm/Writer.cpp
  llvm/lib/MC/WasmObjectWriter.cpp
  llvm/test/MC/WebAssembly/basic-assembly.s


Index: llvm/test/MC/WebAssembly/basic-assembly.s
===================================================================
--- llvm/test/MC/WebAssembly/basic-assembly.s
+++ llvm/test/MC/WebAssembly/basic-assembly.s
@@ -1,10 +1,12 @@
 # RUN: llvm-mc -triple=wasm32-unknown-unknown -mattr=+tail-call,+reference-types,atomics,+simd128,+nontrapping-fptoint,+exception-handling < %s | FileCheck %s
 # Check that it converts to .o without errors, but don't check any output:
 # RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -mattr=+tail-call,+reference-types,+atomics,+simd128,+nontrapping-fptoint,+exception-handling -o %t.o < %s
+# RUN: obj2yaml %t.o | FileCheck %s --check-prefix=OBJ
 
 .functype   something1 () -> ()
 .functype   something2 (i64) -> (i32, f64)
 .functype   something3 () -> (i32)
+.functype   undefined_func () -> (i32)
 .globaltype __stack_pointer, i32
 
 empty_func:
@@ -143,6 +145,7 @@
     .section    .init_array.42,"",@
     .p2align    2
     .int32      test0
+    .int32      undefined_func
 
     .ident      "clang version 9.0.0 (trunk 364502) (llvm/trunk 364571)"
 
@@ -282,9 +285,15 @@
 # CHECK:           .section    .init_array.42,"",@
 # CHECK-NEXT:      .p2align    2
 # CHECK-NEXT:      .int32      test0
+# CHECK-NEXT:      .int32      undefined_func
 
 # CHECK:           .tabletype empty_eref_table, externref
 # CHECK-NEXT: empty_eref_table:
 
 # CHECK:           .tabletype empty_fref_table, funcref
 # CHECK-NEXT: empty_fref_table:
+
+# OBJ:         InitFunctions:
+# OBJ-NEXT:      - Priority:        42
+# OBJ-NEXT:        Symbol:          1
+# OBJ-NEXT: ...
Index: llvm/lib/MC/WasmObjectWriter.cpp
===================================================================
--- llvm/lib/MC/WasmObjectWriter.cpp
+++ llvm/lib/MC/WasmObjectWriter.cpp
@@ -1907,8 +1907,14 @@
         report_fatal_error("symbols in .init_array should exist in symtab");
       if (!TargetSym.isFunction())
         report_fatal_error("symbols in .init_array should be for functions");
-      InitFuncs.push_back(
-          std::make_pair(Priority, TargetSym.getIndex()));
+      // For now, ignore init functions that are not defined within the module.
+      // Ideally undefined init functions should not occur, but they do seem
+      // to be showing up in some hard to reproduce cases involving LTO.
+      // FIXME: Remove this once we find the root cause of
+      // https://github.com/llvm/llvm-project/issues/62243
+      if (TargetSym.isDefined()) {
+        InitFuncs.push_back(std::make_pair(Priority, TargetSym.getIndex()));
+      }
     }
   }
 
Index: lld/wasm/Writer.cpp
===================================================================
--- lld/wasm/Writer.cpp
+++ lld/wasm/Writer.cpp
@@ -1636,6 +1636,9 @@
     const WasmLinkingData &l = file->getWasmObj()->linkingData();
     for (const WasmInitFunc &f : l.InitFunctions) {
       FunctionSymbol *sym = file->getFunctionSymbol(f.Symbol);
+      LLVM_DEBUG(llvm::dbgs() << "calculateInitFunctions: " << file->getName()
+                              << ": " << toString(*sym) << "\n");
+      assert(sym->isDefined());
       // comdat exclusions can cause init functions be discarded.
       if (sym->isDiscarded() || !sym->isLive())
         continue;
Index: lld/wasm/LTO.cpp
===================================================================
--- lld/wasm/LTO.cpp
+++ lld/wasm/LTO.cpp
@@ -35,6 +35,8 @@
 #include <system_error>
 #include <vector>
 
+#define DEBUG_TYPE "lld"
+
 using namespace llvm;
 
 namespace lld::wasm {
@@ -105,6 +107,10 @@
     r.VisibleToRegularObj = config->relocatable || sym->isUsedInRegularObj ||
                             sym->isNoStrip() ||
                             (r.Prevailing && sym->isExported());
+    LLVM_DEBUG(llvm::dbgs()
+               << "LTO: VisibleToRegularObj: " << r.VisibleToRegularObj
+               << " Prevailing: " << r.Prevailing << " " << sym->getName()
+               << " (" << toString(*sym) << ")\n");
     if (r.Prevailing)
       undefine(sym);
 


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