PR for llvm/llvm-project#58277

lld/MachO/UnwindInfoSection.cpp

@@ -158,14 +158,15 @@ class UnwindInfoSectionImpl final : public UnwindInfoSection {
 public:
   UnwindInfoSectionImpl() : cuOffsets(target->wordSize) {}
   uint64_t getSize() const override { return unwindInfoSize; }
-  void prepareRelocations() override;
+  void prepare() override;
   void finalize() override;
   void writeTo(uint8_t *buf) const override;
 
 private:
   void prepareRelocations(ConcatInputSection *);
   void relocateCompactUnwind(std::vector<CompactUnwindEntry> &);
   void encodePersonalities();
+  Symbol *canonicalizePersonality(Symbol *);
 
   uint64_t unwindInfoSize = 0;
   std::vector<decltype(symbols)::value_type> symbolsVec;
@@ -218,14 +219,24 @@ void UnwindInfoSection::addSymbol(const Defined *d) {
   }
 }
 
-void UnwindInfoSectionImpl::prepareRelocations() {
+void UnwindInfoSectionImpl::prepare() {
   // This iteration needs to be deterministic, since prepareRelocations may add
   // entries to the GOT. Hence the use of a MapVector for
   // UnwindInfoSection::symbols.
   for (const Defined *d : make_second_range(symbols))
-    if (d->unwindEntry &&
-        d->unwindEntry->getName() == section_names::compactUnwind)
-      prepareRelocations(d->unwindEntry);
+    if (d->unwindEntry) {
+      if (d->unwindEntry->getName() == section_names::compactUnwind) {
+        prepareRelocations(d->unwindEntry);
+      } else {
+        // We don't have to add entries to the GOT here because FDEs have
+        // explicit GOT relocations, so Writer::scanRelocations() will add those
+        // GOT entries. However, we still need to canonicalize the personality
+        // pointers (like prepareRelocations() does for CU entries) in order
+        // to avoid overflowing the 3-personality limit.
+        FDE &fde = cast<ObjFile>(d->getFile())->fdes[d->unwindEntry];
+        fde.personality = canonicalizePersonality(fde.personality);
+      }
+    }
 }
 
 // Compact unwind relocations have different semantics, so we handle them in a
@@ -279,6 +290,7 @@ void UnwindInfoSectionImpl::prepareRelocations(ConcatInputSection *isec) {
           continue;
       }
 
+      // Similar to canonicalizePersonality(), but we also register a GOT entry.
       if (auto *defined = dyn_cast<Defined>(s)) {
         // Check if we have created a synthetic symbol at the same address.
         Symbol *&personality =
@@ -291,6 +303,7 @@ void UnwindInfoSectionImpl::prepareRelocations(ConcatInputSection *isec) {
         }
         continue;
       }
+
       assert(isa<DylibSymbol>(s));
       in.got->addEntry(s);
       continue;
@@ -320,6 +333,18 @@ void UnwindInfoSectionImpl::prepareRelocations(ConcatInputSection *isec) {
   }
 }
 
+Symbol *UnwindInfoSectionImpl::canonicalizePersonality(Symbol *personality) {
+  if (auto *defined = dyn_cast_or_null<Defined>(personality)) {
+    // Check if we have created a synthetic symbol at the same address.
+    Symbol *&synth = personalityTable[{defined->isec, defined->value}];
+    if (synth == nullptr)
+      synth = defined;
+    else if (synth != defined)
+      return synth;
+  }
+  return personality;
+}
+
 // We need to apply the relocations to the pre-link compact unwind section
 // before converting it to post-link form. There should only be absolute
 // relocations here: since we are not emitting the pre-link CU section, there

lld/MachO/UnwindInfoSection.h

@@ -24,7 +24,7 @@ class UnwindInfoSection : public SyntheticSection {
   // section entirely.
   bool isNeeded() const override { return !allEntriesAreOmitted; }
   void addSymbol(const Defined *);
-  virtual void prepareRelocations() = 0;
+  virtual void prepare() = 0;
 
 protected:
   UnwindInfoSection();

lld/MachO/Writer.cpp

@@ -675,7 +675,7 @@ void Writer::scanRelocations() {
     }
   }
 
-  in.unwindInfo->prepareRelocations();
+  in.unwindInfo->prepare();
 }
 
 void Writer::scanSymbols() {

lld/test/MachO/eh-frame-personality-dedup.s

@@ -0,0 +1,43 @@
+# REQUIRES: x86
+# RUN: rm -rf %t; split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin19.0.0 %t/eh-frame.s -o %t/eh-frame.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin19.0.0 %t/cu.s -o %t/cu.o
+# RUN: %lld -dylib %t/cu.o %t/eh-frame.o -o %t/out
+
+## Sanity check: we want our input to contain a section (and not symbol)
+## relocation for the personality reference.
+# RUN: llvm-readobj --relocations %t/cu.o | FileCheck %s --check-prefix=SECT-RELOC
+# SECT-RELOC:      Section __compact_unwind {
+# SECT-RELOC-NEXT:   __text
+# SECT-RELOC-NEXT:   __text
+# SECT-RELOC-NEXT: }
+
+## Verify that the personality referenced via a symbol reloc in eh-frame.s gets
+## dedup'ed with the personality referenced via a section reloc in cu.s.
+# RUN: llvm-objdump --macho --unwind-info %t/out | FileCheck %s
+# CHECK: Personality functions: (count = 1)
+
+#--- eh-frame.s
+_fun:
+  .cfi_startproc
+  .cfi_personality 155, _my_personality
+  ## cfi_escape cannot be encoded in compact unwind
+  .cfi_escape 0
+  ret
+  .cfi_endproc
+
+.subsections_via_symbols
+
+#--- cu.s
+.globl _my_personality
+_fun:
+  .cfi_startproc
+  .cfi_personality 155, _my_personality
+  .cfi_def_cfa_offset 16
+  ret
+  .cfi_endproc
+
+_my_personality:
+  nop
+
+.subsections_via_symbols