Question 1

How do I parse a Mach-O file header in C?

Accepted Answer

Use the mach_header or mach_header_64 structs defined in the reference, reading from the file offset. Check the magic field for endianness and filetype for the format, as detailed in the header structure section.

Question 2

What's the difference between Mach-O and ELF file formats?

Accepted Answer

Mach-O is used by macOS/iOS with segments like __TEXT and __DATA, while ELF is common on Linux/Unix with different section and program header layouts. Mach-O supports features like two-level namespaces, as explained in the dynamic linking details.

Question 3

How does dynamic linking work in Mach-O files?

Accepted Answer

It uses load commands such as LC_LOAD_DYLIB to list dependent libraries and sections like __la_symbol_ptr for lazy binding. The dynamic linker processes these at runtime, as covered in the segment and load command documentation.

Question 4

What tools can I use to inspect Mach-O files on macOS?

Accepted Answer

Command-line tools like otool and objdump are standard; the reference helps interpret their output by explaining structures like sections and symbols, but it doesn't provide tool usage instructions.

Question 5

How to create a simple Mach-O executable from assembly code?

Accepted Answer

Assemble the code into an object file using as, then link with ld to produce a Mach-O executable, ensuring the header and segment commands align with the spec, though the reference lacks step-by-step guides.

Question 6

What are the common sections in the __DATA segment?

Accepted Answer

Includes __data for initialized mutable variables, __bss for uninitialized statics, and __la_symbol_ptr for lazy symbol pointers, as listed in Table 2 of the README with explanations of each.

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