[PATCH] D64148: [lld][WebAssembly] Fix __start/__stop symbols when combining input segments

[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.

We should be generating one __start/__stop pair per output segment
not per input segment.  The test wasn't catching this because it was
only linking a single object file.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D64148

Files:
  lld/test/wasm/Inputs/explicit-section.ll
  lld/test/wasm/startstop.ll
  lld/wasm/Writer.cpp


Index: lld/wasm/Writer.cpp
===================================================================
--- lld/wasm/Writer.cpp
+++ lld/wasm/Writer.cpp
@@ -73,7 +73,6 @@
   void addSection(OutputSection *Sec);
 
   void addSections();
-  void addStartStopSymbols(const InputSegment *Seg);
 
   void createCustomSections();
   void createSyntheticSections();
@@ -302,15 +301,15 @@
 // __stop_<secname> symbols. They are at beginning and end of the section,
 // respectively. This is not requested by the ELF standard, but GNU ld and
 // gold provide the feature, and used by many programs.
-void Writer::addStartStopSymbols(const InputSegment *Seg) {
-  StringRef S = Seg->getName();
-  LLVM_DEBUG(dbgs() << "addStartStopSymbols: " << S << "\n");
-  if (!isValidCIdentifier(S))
+static void addStartStopSymbols(const OutputSegment *Seg) {
+  StringRef Name = Seg->Name;
+  LLVM_DEBUG(dbgs() << "addStartStopSymbols: " << Name << "\n");
+  if (!isValidCIdentifier(Name))
     return;
-  uint32_t Start = Seg->OutputSeg->StartVA + Seg->OutputSegmentOffset;
-  uint32_t Stop = Start + Seg->getSize();
-  Symtab->addOptionalDataSymbol(Saver.save("__start_" + S), Start);
-  Symtab->addOptionalDataSymbol(Saver.save("__stop_" + S), Stop);
+  uint32_t Start = Seg->StartVA;
+  uint32_t Stop = Start + Seg->Size;
+  Symtab->addOptionalDataSymbol(Saver.save("__start_" + Name), Start);
+  Symtab->addOptionalDataSymbol(Saver.save("__stop_" + Name), Stop);
 }
 
 void Writer::addSections() {
@@ -766,8 +765,7 @@
     // Create linker synthesized __start_SECNAME/__stop_SECNAME symbols
     // This has to be done after memory layout is performed.
     for (const OutputSegment *Seg : Segments)
-      for (const InputSegment *S : Seg->InputSegments)
-        addStartStopSymbols(S);
+      addStartStopSymbols(Seg);
   }
 
   log("-- scanRelocations");
Index: lld/test/wasm/startstop.ll
===================================================================
--- lld/test/wasm/startstop.ll
+++ lld/test/wasm/startstop.ll
@@ -1,5 +1,6 @@
 ; RUN: llc -filetype=obj -o %t.o %s
-; RUN: wasm-ld --no-gc-sections %t.o -o %t.wasm
+; RUN: llc -filetype=obj %p/Inputs/explicit-section.ll -o %t2.o
+; RUN: wasm-ld --no-gc-sections --export=var1 %t.o %t2.o -o %t.wasm
 ; RUN: obj2yaml %t.wasm | FileCheck %s
 
 target triple = "wasm32-unknown-unknown"
@@ -32,7 +33,7 @@
 ; CHECK-NEXT:         Body:            4180888080000B
 ; CHECK-NEXT:       - Index:           2
 ; CHECK-NEXT:         Locals:          []
-; CHECK-NEXT:         Body:            4188888080000B
+; CHECK-NEXT:         Body:            4190888080000B
 ; CHECK-NEXT:       - Index:           3
 ; CHECK-NEXT:         Locals:          []
 ; CHECK-NEXT:         Body:            0B
@@ -43,7 +44,7 @@
 ; CHECK-NEXT:         Offset:
 ; CHECK-NEXT:           Opcode:          I32_CONST
 ; CHECK-NEXT:           Value:           1024
-; CHECK-NEXT:         Content:         '0300000004000000'
+; CHECK-NEXT:         Content:         03000000040000002A0000002B000000
 ; CHECK-NEXT:   - Type:            CUSTOM
 ; CHECK-NEXT:     Name:            name
 ; CHECK-NEXT:     FunctionNames:
Index: lld/test/wasm/Inputs/explicit-section.ll
===================================================================
--- /dev/null
+++ lld/test/wasm/Inputs/explicit-section.ll
@@ -0,0 +1,4 @@
+target triple = "wasm32-unknown-unknown"
+
+ at var1 = global i32 42, section "mysection", align 4
+ at var2 = global i32 43, section "mysection", align 4


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