alt Hacker News> Whereas, with ELF – if you want to add a new feature, do you add it as a new program table entry type (PT_), or a new note type (NT_), or a separate note section (SHT_NOTE)?
It won't be a note section since ELF binaries don't need to have any sections. You can remove all section headers from an existing ELF binary and it'll still work (sstrip [https://github.com/aunali1/super-strip - not sure the one in ELFkickers is the same thing] does this).
Program headers define how & where to load things, notes are for small metadata.
Is your point that section headers do generally exist in ELF files, even though they're not necessary? I do agree that this "double indexing" between PHs and SHs is pretty weird and a bit odd.
Well, you'll have a SHT_NOTE section and then PT_NOTE pointing to its contents, right? So that way the notes are accessible both via section headers and program headers.
Mach-O does similarly have a distinction between sections as a link-time view, and segments as an execution-time view – a Mach-O contains one or more segments (LC_SEGMENT for 32-bit, LC_SEGMENT_64 for 64-bit), each of which contains a segment header followed by zero or more section headers, so the sections are subdivisions of the segment. Mach-O has names for both segments and sections; ELF only has names for sections.
Let me put it this way – if you wanted to add embedded digital signatures to ELF, so the kernel could verify them at runtime, similar to Mach-O LC_CODE_SIGNATURE – what is the extension point you'd use? The Linux kernel supports digital signatures for ELF executables in conjunction with IMA, but instead of storing the signature in the executable like Mach-O does, it stores it in a filesystem xattr.