[lld-macho] Fix symbol relocs handling for LSDAs

[int3]

Summary

Similar to D113702, but for the LSDAs. Clang seems to emit all LSDA
relocs as section relocs, but ld -r can turn those relocs into symbol
ones.

[int3]

update

[oontvoo]

LG Thanks!!!

lld/MachO/UnwindInfoSection.cpp

442–443

Thank you!!! was wondering why our build was crashing at this line today.

assert.h assertion failed at llvm/include/llvm/ADT/PointerUnion.h:159 in T llvm::PointerUnion<lld::macho::Symbol *, lld::macho::InputSection *>::get() const [PTs = <lld::macho::Symbol *, lld::macho::InputSection *>, T = lld::macho::InputSection *]: is<T>() && "Invalid accessor called"

lld/test/MachO/compact-unwind-sym-relocs.s

246–250 ↗

(On Diff #386684)

dont need these?

[oontvoo]

P.S: build failures look real - PTAL

[int3]

fix

lld/MachO/UnwindInfoSection.cpp

while (++foldEnd < cuIndices.end() &&
            canFoldEncoding(cuEntries[*foldEnd].encoding)) {
       // In most cases, we can just compare the values of cuEntries[*].lsda.
       // However, it is possible for -rename_section to cause the LSDA section
       // (__gcc_except_tab) to be finalized after the unwind info section. In
       // that case, we don't yet have unique addresses for the LSDA entries.
       // So we check their relocations instead.
       // FIXME: should we account for an LSDA at an absolute address? ld64 seems
       // to support it, but it seems unlikely to be used in practice.
+      fprintf(stderr, "wtf0\n");
       Reloc *lsda1 =
           findLsdaReloc(symbolsVec[*foldBegin].second->compactUnwind);
       Reloc *lsda2 = findLsdaReloc(symbolsVec[*foldEnd].second->compactUnwind);
       if (lsda1 == nullptr && lsda2 == nullptr)
         continue;
       if (lsda1 == nullptr || lsda2 == nullptr)
         break;
-      if (lsda1->referent.get<InputSection *>() !=
-          lsda2->referent.get<InputSection *>())
+      if (lsda1->referent != lsda2->referent)
         break;
       if (lsda1->addend != lsda2->addend)
         break;
     }
     *foldWrite++ = *foldBegin;
     foldBegin = foldEnd;
   }
   cuIndices.erase(foldWrite, cuIndices.end());
if (i < cuIndices.size() &&
                                  cuIndices.size() - page.entryIndex);
       i = page.entryIndex + page.entryCount;
     } else {
       page.kind = UNWIND_SECOND_LEVEL_COMPRESSED;
     }
   }
 
   for (size_t idx : cuIndices) {
-    const CompactUnwindEntry<Ptr> &cu = cuEntries[idx];
     lsdaIndex[idx] = entriesWithLsda.size();
-    if (cu.lsda != 0)
+    if (findLsdaReloc(symbolsVec[idx].second->compactUnwind))
       entriesWithLsda.push_back(idx);
   }
 
   // compute size of __TEXT,__unwind_info section
   level2PagesOffset = sizeof(unwind_info_section_header) +
                       commonEncodings.size() * sizeof(uint32_t) +
                       personalities.size() * sizeof(uint32_t) +
                       // The extra second-level-page entry is for the sentinel
void UnwindInfoSectionImpl<Ptr>::writeTo(uint8_t *buf) const {
 
   // LSDAs
   auto *lep =
       reinterpret_cast<unwind_info_section_header_lsda_index_entry *>(iep);
   for (size_t idx : entriesWithLsda) {
     const CompactUnwindEntry<Ptr> &cu = cuEntries[idx];
     const Defined *d = symbolsVec[idx].second;
     if (Reloc *r = findLsdaReloc(d->compactUnwind)) {
-      auto *isec = r->referent.get<InputSection *>();
-      lep->lsdaOffset = isec->getVA(r->addend) - in.header->addr;
+      uint64_t va;
+      if (auto *isec = r->referent.dyn_cast<InputSection *>()) {
+        va = isec->getVA(r->addend);
+      } else {
+        auto *sym = r->referent.get<Symbol *>();
+        va = sym->getVA() + r->addend;
+      }
+      lep->lsdaOffset = va - in.header->addr;
     }
     lep->functionOffset = cu.functionAddress - in.header->addr;
     lep++;
   }
 
   // Level-2 pages
   auto *pp = reinterpret_cast<uint32_t *>(lep);
   for (const SecondLevelPage &page : secondLevelPages) {

lld/test/MachO/compact-unwind-r.s

+# REQUIRES: x86
+# RUN: rm -rf %t; mkdir -p %t
+# RUN: yaml2obj %s > %t/test.o
+# RUN: %lld -dylib -lc++ %t/test.o -o %t/test
+# RUN: llvm-objdump --macho --syms --unwind-info %t/test | FileCheck %s
+
+# CHECK:      SYMBOL TABLE:
+# CHECK-DAG:  [[#%x,MAIN:]]        l     F __TEXT,__text _main
+# CHECK-DAG:  [[#%x,EXCEPT0:]]     l     O __TEXT,__gcc_except_tab _exception0
+
+# CHECK:      LSDA descriptors:
+# CHECK-NEXT:   [0]: function offset=0x[[#%.8x,MAIN]], LSDA offset=0x[[#%.8x,EXCEPT0]]
+
+## The YAML was generated from compiling the following code and then running it
+## through `ld -r`, which converts the functionAddress and LSDA relocations from
+## section- to symbol-based ones. This test covers the LSDA symbol relocation;
+## the functionAddress relocation is handled in weak-definition-gc.s.
+##
+## .text
+## .p2align 2
+## _main:
+##   .cfi_startproc
+##   .cfi_personality 155, ___gxx_personality_v0
+##   .cfi_lsda 16, _exception0
+##   .cfi_def_cfa_offset 16
+##   ret
+##   .cfi_endproc
+## 
+## .section __TEXT,__gcc_except_tab
+## _exception0:
+##   .space 0
+## 
+## .subsections_via_symbols
+
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x1000007
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+LoadCommands:
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+    segname:         ''
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+        relocations:
+          - address:         0x13
+            symbolnum:       4
+            pcrel:           true
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+            pcrel:           false
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+        relocations:
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+  - cmd:             LC_SYMTAB
+    cmdsize:         24
+    symoff:          728
+    nsyms:           5
+    stroff:          808
+    strsize:         64
+LinkEditData:
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+    - n_strx:          24
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+    - ' '
+    - ___gxx_personality_v0
+    - _main
+    - _exception0
+    - EH_Frame1
+    - func.eh
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+    - ''
+    - ''
+    - ''
+...