NRO

NRO is the executable format for non-ExeFS binaries.

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

Start

Offset	Size	Description
0x0	0x4	Unused. Originally 0x0, with [17.0.0+] this is set to value 0x1.
0x4	0x4	MOD0 offset
0x8	0x4	[1.0.0-16.1.0] Padding. [17.0.0+] nnSdk version offset
0xC	0x4	Padding

Header

Offset	Size	Description
0x0	0x4	Magic "NRO0"
0x4	0x4	Version (always 0)
0x8	4	Size (total NRO file size)
0xC	0x4	Flags (unused)
0x10	0x8 * 3	SegmentHeader[3] {.text, .ro, .data}
0x28	0x4	BssSize
0x2C	0x4	Reserved
0x30	0x20	ModuleId
0x50	0x04	DsoHandleOffset (unused)
0x54	0x04	Reserved (unused)
0x58	0x8 * 3	SegmentHeader[3] {.apiInfo, .dynstr, .dynsym}

SegmentHeader

Offset	Size	Description
0x0	0x4	MemoryOffset
0x4	0x4	Size

ModuleId

Value of "build id" from ELF's GNU .note section. Contains variable sized digest, up to 32bytes.

Assets

This is an optional custom assets section for homebrew, this is located at file offset {NroHeader.size}. See also switch-tools for implementation.

The below offsets are relative to the beginning of the assets section (AssetHeader).

AssetHeader

Offset	Size	Description
0x0	0x4	Magic "ASET"
0x4	0x4	Format version, currently 0.
0x8	0x10	AssetSection icon. Used by the Homebrew Launcher. Like official icons, this is a 256x256 JPEG.
0x18	0x10	AssetSection NACP. Used by the Homebrew Launcher.
0x28	0x10	AssetSection romfs. Can be used by the application.

AssetSection

Offset	Size	Description
0x0	0x8	Offset
0x8	0x8	Size, 0 indicates this section is empty.