Nintendo Switch Brew

NSO: Difference between revisions

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NSO is the main executable format.
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):
It starts with the "NSO" header and mainly describes .text, .rodata, and .data segments (like a short-form of ELF program headers). If the segments are compressed, they are compressed using LZ4.


= NSO Header =
= NsoHeader =
{| class="wikitable" border="1"
{| class="wikitable" border="1"
|-
|-
Line 12: Line 12:
| 0x0
| 0x0
| 4
| 4
| Magic "NSO0"
| Signature ("NSO0")
|-
|-
| 0x4
| 0x4
| 4
| 4
|  
| Version
|-
|-
| 0x8
| 0x8
| 4
| 4
|  
| Reserved
|-
|-
| 0xC
| 0xC
| 4
| 4
| Flags, bit 0-2: section is compressed, bit 3-5: check section hash when loading
| [[#Flags|Flags]]
|-
|-
| 0x10
| 0x10
| 0x10 * 3
| 0x4
| SegmentHeader[3]
| TextFileOffset
|-
| 0x14
| 0x4
| TextMemoryOffset
|-
| 0x18
| 0x4
| TextSize
|-
| 0x1C
| 0x4
| ModuleNameOffset (calculated by sizeof(header))
|-
| 0x20
| 0x4
| RoFileOffset
|-
| 0x24
| 0x4
| RoMemoryOffset
|-
| 0x28
| 0x4
| RoSize
|-
| 0x2C
| 0x4
| ModuleNameSize
|-
| 0x30
| 0x4
| DataFileOffset
|-
| 0x34
| 0x4
| DataMemoryOffset
|-
| 0x38
| 0x4
| DataSize
|-
| 0x3C
| 0x4
| BssSize
|-
|-
| 0x40
| 0x40
| 0x20
| 0x20
| Value of "build id" from ELF's GNU .note section. Contains variable sized digest, up to 32bytes.
| [[#ModuleId|ModuleId]]
|-
|-
| 0x60
| 0x60
| 0x4 * 3
| 0x4
| CompressedSize[3]
| TextFileSize (.text compressed size)
|-
|-
| 0x6c
| 0x64
| 0x24
| 0x4
| Padding
| RoFileSize (.rodata compressed size)
|-
|-
| 0x90
| 0x68
| 8
| 0x4
| .rodata-relative extents of .dynstr
| DataFileSize (.data compressed size)
|-
|-
| 0x98
| 0x6C
| 8
| 0x1C
| .rodata-relative extents of .dynsym
| Reserved
|-
|-
| 0xA0
| 0x88
| 0x20 * 3
| 0x4
| SHA256 hashes over the decompressed sections using the above byte-sizes: .text, .rodata, and .data.
| EmbeddedOffset (relative to the .rodata section)
|-
|-
| 0x100
| 0x8C
|
| 0x4
| Compressed sections
| EmbeddedSize
|}
 
Most data in Switch binaries are standard ELF structures, however some are custom.
For example, the MOD header is essentially a replacement for a PT_DYNAMIC program header.
 
== SegmentHeader ==
{| class="wikitable" border="1"
|-
|-
! Offset
| 0x90
! Size
| 0x4
! Description
| DynStrOffset (relative to the .rodata section)
|-
|-
| 0x0
| 0x94
| 4
| 0x4
| FileOffset
| DynStrSize
|-
|-
| 0x98
| 0x4
| 0x4
| 4
| DynSymOffset (relative to the .rodata section)
| MemoryOffset
|-
|-
| 0x8
| 0x9C
| 4
| 0x4
| DecompressedSize
| DynSymSize
|-
|-
| 0xC
| 0xA0
| 4
| 0x20
| UnkOffset/UnkSize/BssSize
| TextHash (SHA-256 hash over the decompressed .text section using the above size)
|}
 
== .rodata-relative extent ==
{| class="wikitable" border="1"
|-
|-
! Offset
| 0xC0
! Size
| 0x20
! Description
| RoHash (SHA-256 hash over the decompressed .rodata section using the above size)
|-
|-
| 0x0
| 0xE0
| 4
| 0x20
| RegionRoDataOffset
| DataHash (SHA-256 hash over the decompressed .data section using the above size)
|-
|-
| 0x4
| 0x100
| 4
| Variable
| RegionSize
| Compressed sections
|}
|}


== MOD ==
== Flags ==
All offsets are signed 32bit values relative to the magic field.
The 32bits at image base + 4 must point to the magic field.
The MOD structure is designed such that it can be placed at image base and point to itself.
The 2 fields preceding the magic field get copied around with the structure, even if it is relocated to somewhere besides the image base. If MOD is not located at image base, the value at offset 4 must still point to the MOD magic. In the case of .text being at image base, this implies that the first instruction can only be an unconditional branch over the offset literal.
{| class="wikitable" border="1"
{| class="wikitable" border="1"
|-
|-
! Offset
! Bits
! Size
! Description
! Description
|-
|-
| 0x00
| 0
| 4
| TextCompress (.text section is compressed)
| ZeroPadding
|-
|-
| 0x04
| 1
| 4
| RoCompress (.rodata section is compressed)
| MagicOffset. Always 8 (so it works when MOD is at image_base + 0).
|-
|-
| 0x08
| 2
| 4
| DataCompress (.data section is compressed)
| Magic "MOD0"
|-
|-
| 0x0C
| 3
| 4
| TextHash (.text hash must be checked when loading)
| .dynamic offset
|-
|-
| 0x10
| 4
| 4
| .bss start offset
| RoHash (.rodata hash must be checked when loading)
|-
|-
| 0x14
| 5
| 4
| DataHash (.data hash must be checked when loading)
| .bss end offset
|-
| 0x18
| 4
| .eh_frame_hdr start offset
|-
| 0x1C
| 4
| .eh_frame_hdr end offset
|-
| 0x20
| 4
| offset to runtime-generated module object. typically equal to .bss base.
|}
|}


=Arguments=
== ModuleId ==
Loader maps memory and writes the [[Loader_services#AddProcessToLaunchQueue|arguments]] to {end of rwdata section specified by last SegmentHeader}. Official processes use argdata_addr = {page-aligned _end}. svcQueryMemory is used by official sw to verify that argdata_addr is mapped RW, since this memory is only mapped when arguments are specified via that command. Afterwards, official sw aligns the argdata_addr to 4-bytes. Structure located at argdata_addr:
This is "nn::ro::detail::ModuleId".
 
Value of "build id" from ELF's GNU .note section. Contains variable sized digest, up to 32bytes.
 
= Arguments =
[[Loader_services|Loader]] maps memory and writes the [[Loader_services#SetProgramArgument|arguments]] to {end of rwdata section}. Official processes use argdata_addr = {page-aligned _end}. svcQueryMemory is used by official sw to verify that argdata_addr is mapped RW, since this memory is only mapped when arguments are specified via that command. Afterwards, official sw aligns the argdata_addr to 4-bytes.


The structure located at argdata_addr is as follows:
{| class="wikitable" border="1"
{| class="wikitable" border="1"
|-
|-
Retrieved from "https://switchbrew.org/wiki/NSO"