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

[oontvoo]

Summary

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

[oontvoo]

rebase

[MaskRay]

lld/MachO/Arch/ARM64.cpp

608

secIt >= obj.sections.end() should be impossible.

It's better to check whether the upper_bound result is out-of-bounds before invoking std::prev.

[oontvoo]

updated diff

lld/MachO/Arch/ARM64.cpp

608

turnt out we can simply check whether sections or subsections are empty to avoid getting an out-of-bound iter.

[oontvoo]

@MaskRay Hi, friendly ping? Thanks!

[MaskRay]

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

Running. Can you name the exact test names?

[oontvoo]

In D157027#4578002, @MaskRay wrote:

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

Running. Can you name the exact test names?

It's an internal test case - dropped you a link to it in chat.

P.S: can try making a smaller repro to attach to this.

lld/MachO/Arch/ARM64.cpp

void ARM64::applyOptimizationHints(uint8_t *outBuf, const ObjFile &obj) const {
   auto findSection = [&](uint64_t addr) {
     if (section && addr >= sectionAddr &&
         addr < sectionAddr + section->getSize())
       return true;
 
     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);
     if (!isec || isec->shouldOmitFromOutput())
       return false;
 
     section = isec;
     sectionAddr = subsec.offset + sec->addr;