[llvm] r332517 - [WebAssembly] MC: Ensure that FUNCTION_OFFSET relocations are always against function symbols.

[Sam Clegg via llvm-commits]

Author: sbc
Date: Wed May 16 13:09:05 2018
New Revision: 332517

URL: http://llvm.org/viewvc/llvm-project?rev=332517&view=rev
Log:
[WebAssembly] MC: Ensure that FUNCTION_OFFSET relocations are always against function symbols.

The getAtom() method wasn't doing what we needed in all cases. We want
the symbols for the function which defines that section. We can compute
this easily enough and we know that we have at most one function in each
section.

Once this lands I will revert rL331412 which is no longer needed.

Fixes PR37409

Differential Revision: https://reviews.llvm.org/D46970

Modified:
    llvm/trunk/lib/MC/WasmObjectWriter.cpp
    llvm/trunk/test/MC/WebAssembly/debug-info.ll

Modified: llvm/trunk/lib/MC/WasmObjectWriter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/WasmObjectWriter.cpp?rev=332517&r1=332516&r2=332517&view=diff
==============================================================================
--- llvm/trunk/lib/MC/WasmObjectWriter.cpp (original)
+++ llvm/trunk/lib/MC/WasmObjectWriter.cpp Wed May 16 13:09:05 2018
@@ -225,6 +225,9 @@ class WasmObjectWriter : public MCObject
   DenseMap<const MCSectionWasm *, std::vector<WasmRelocationEntry>>
       CustomSectionsRelocations;
 
+  // Map from section to fintining function.
+  DenseMap<const MCSection *, const MCSymbol *> SectionFunctions;
+
   DenseMap<WasmFunctionType, int32_t, WasmFunctionTypeDenseMapInfo>
       FunctionTypeIndices;
   SmallVector<WasmFunctionType, 4> FunctionTypes;
@@ -265,6 +268,7 @@ private:
     FunctionTypes.clear();
     Globals.clear();
     DataSegments.clear();
+    SectionFunctions.clear();
     MCObjectWriter::reset();
     NumFunctionImports = 0;
     NumGlobalImports = 0;
@@ -383,6 +387,18 @@ void WasmObjectWriter::writeHeader(const
 
 void WasmObjectWriter::executePostLayoutBinding(MCAssembler &Asm,
                                                 const MCAsmLayout &Layout) {
+  // Build a map of sections to the function that defines them, for use
+  // in recordRelocation.
+  for (const MCSymbol &S : Asm.symbols()) {
+    const auto &WS = static_cast<const MCSymbolWasm &>(S);
+    if (WS.isDefined() && WS.isFunction() && !WS.isVariable()) {
+      const auto &Sec = static_cast<const MCSectionWasm &>(S.getSection());
+      auto Pair = SectionFunctions.insert(std::make_pair(&Sec, &S));
+      if (!Pair.second)
+        report_fatal_error("section already has a defining function: " +
+                           Sec.getSectionName());
+    }
+  }
 }
 
 void WasmObjectWriter::recordRelocation(MCAssembler &Asm,
@@ -475,7 +491,7 @@ void WasmObjectWriter::recordRelocation(
     const MCSymbol *SectionSymbol = nullptr;
     const MCSection &SecA = SymA->getSection();
     if (SecA.getKind().isText())
-      SectionSymbol = SecA.begin()->getAtom();
+      SectionSymbol = SectionFunctions.find(&SecA)->second;
     else
       SectionSymbol = SecA.getBeginSymbol();
     if (!SectionSymbol)

Modified: llvm/trunk/test/MC/WebAssembly/debug-info.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/WebAssembly/debug-info.ll?rev=332517&r1=332516&r2=332517&view=diff
==============================================================================
--- llvm/trunk/test/MC/WebAssembly/debug-info.ll (original)
+++ llvm/trunk/test/MC/WebAssembly/debug-info.ll Wed May 16 13:09:05 2018
@@ -204,6 +204,13 @@
 ; CHECK-NEXT:  }
 ; CHECK-NEXT:]
 
+; generated from the following C code using: clang --target=wasm32 -g -O0 -S -emit-llvm test.c
+; extern int myextern;
+; void f2(void) { return; }
+;
+; int* foo = &myextern;
+; void (*ptr2)(void) = f2;
+
 target triple = "wasm32-unknown-unknown"
 
 source_filename = "test.c"
@@ -226,7 +233,7 @@ attributes #0 = { noinline nounwind optn
 
 !0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
 !1 = distinct !DIGlobalVariable(name: "foo", scope: !2, file: !3, line: 4, type: !11, isLocal: false, isDefinition: true)
-!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 6.0.0 (trunk 315924) (llvm/trunk 315960)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 7.0.0 (trunk 332303) (llvm/trunk 332406)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
 !3 = !DIFile(filename: "test.c", directory: "/usr/local/google/home/sbc/dev/wasm/simple")
 !4 = !{}
 !5 = !{!0, !6}
@@ -240,6 +247,6 @@ attributes #0 = { noinline nounwind optn
 !13 = !{i32 2, !"Dwarf Version", i32 4}
 !14 = !{i32 2, !"Debug Info Version", i32 3}
 !15 = !{i32 1, !"wchar_size", i32 4}
-!16 = !{!"clang version 6.0.0 (trunk 315924) (llvm/trunk 315960)"}
+!16 = !{!"clang version 7.0.0 (trunk 332303) (llvm/trunk 332406)"}
 !17 = distinct !DISubprogram(name: "f2", scope: !3, file: !3, line: 2, type: !9, isLocal: false, isDefinition: true, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false, unit: !2, retainedNodes: !4)
-!18 = !DILocation(line: 2, column: 16, scope: !17)
+!18 = !DILocation(line: 2, column: 17, scope: !17)