NSO

NSO is the main executable format.

It starts with the "NSO" header and mainly describes .text, .rodata, and .data segments (like a short-form of ELF program headers):

SegmentHeader

Offset	Size	Description
0x0	4	file offset of data
0x4	4	memory offset loaded to
0x8	4	size of data copied to memory offset (i.e. size after decompression)
0xC	4	alignment used on memory size / size of .bss in the case of .data segment

.rodata-relative extent

Offset	Size	Description
0x0	4	offset (relative to .rodata)
0x4	4	size of region

NSO Header

Offset	Size	Description
0x0	4	Magic "NSO0"
0x4	4
0x8	4
0xC	4	Always 0x3f?
0x10	0x10 * 3	SegmentHeader for each segment
0x40	0x20	Value of "build id" from ELF's GNU .note section. Contains variable sized digest, up to 32bytes.
0x60	0x4 * 3	file size of each segment (i.e. LZ4-compressed size)
0x6c	0x24	Padding
0x90	8	.rodata-relative extents of .dynstr
0x98	8	.rodata-relative extents of .dynsym
0xA0	0x20 * 3	SHA256 hashes over the decompressed sections using the above byte-sizes: .text, .rodata, and .data.
0x100		Compressed sections