[Lldb-commits] [lldb] Enable LLDB to load large dSYM files. (PR #164471)

[Ellis Hoag via lldb-commits]

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@@ -1697,6 +1701,14 @@ void ObjectFileMachO::ProcessSegmentCommand(
     // isn't stored in the abstracted Sections.
     m_mach_sections.push_back(sect64);
 
+    // Make sure we can load dSYM files whose __DWARF sections exceed the 4GB
+    // barrier. llvm::MachO::section_64 have only 32 bit file offsets for the
+    // section contents.
+    const uint64_t section_file_offset = sect64.offset + section_offset_adjust;
+    // If this section overflows a 4GB barrier, then we need to adjust any
+    // subsequent the section offsets.
+    if (is_dsym && ((uint64_t)sect64.offset + sect64.size) >= UINT32_MAX)
+      section_offset_adjust += 0x100000000ull;
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ellishg wrote:

Right, I think this won't work if the section size is > 8GB, which is not the case in your examples (I know the example is contrived, but not impossible). If the offset + size spills over 4GB, then we need to add `0x100000000ull` like we do here. We can see file offset of `__debug_aranges ` is `0x17705c6fb ` rather than `0x7705c6fb `. But imagine if the size of the prior section `__debug_info` was 4GB larger. Then we would need to add `0x200000000ull` to the file offset of the next section `__debug_aranges` to get `0x27705c6fb`.

In the code, we don't just want to add `0x100000000ull`, we want to add `0x100000000ull * N` where N is the number of 4GB boundaries that the section crosses. That is basically the math I was attempting to do with the bit mask.

https://github.com/llvm/llvm-project/pull/164471