[PATCH] D157027: [lld-macho][nfc]Add bounds check before attempting to dereferencing iterators.

[Vy Nguyen via Phabricator via llvm-commits]

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Runnign some tests with asan built of LLD would throw errors similar to the following:

AddressSanitizer:DEADLYSIGNAL

  #0 0x55d8e6da5df7 in operator() /mnt/ssd/repo/lld/llvm-project/lld/MachO/Arch/ARM64.cpp:612
  #1 0x55d8e6daa514 in operator() /mnt/ssd/repo/lld/llvm-project/lld/MachO/Arch/ARM64.cpp:650


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D157027

Files:
  lld/MachO/Arch/ARM64.cpp


Index: lld/MachO/Arch/ARM64.cpp
===================================================================
--- lld/MachO/Arch/ARM64.cpp
+++ lld/MachO/Arch/ARM64.cpp
@@ -605,11 +605,18 @@
     auto secIt = std::prev(llvm::upper_bound(
         obj.sections, addr,
         [](uint64_t off, const Section *sec) { return off < sec->addr; }));
+    if (secIt < obj.sections.begin() || secIt > obj.sections.end() ||
+        secIt == obj.sections.end())
+      return false;
     const Section *sec = *secIt;
 
     auto subsecIt = std::prev(llvm::upper_bound(
         sec->subsections, addr - sec->addr,
         [](uint64_t off, Subsection subsec) { return off < subsec.offset; }));
+    if (subsecIt < sec->subsections.begin() ||
+        subsecIt > sec->subsections.end() || subsecIt == sec->subsections.end())
+      return false;
+
     const Subsection &subsec = *subsecIt;
     const ConcatInputSection *isec =
         dyn_cast_or_null<ConcatInputSection>(subsec.isec);


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