Nintendo Switch Brew

NSO: Difference between revisions

← Older edit
No edit summary
No edit summary
 
(19 intermediate revisions by 7 users not shown)
Line 1: Line 1:
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.


=== .rodata-relative extent ===
= NsoHeader =
{| class="wikitable" border="1"
{| class="wikitable" border="1"
|-
|-
Line 12: Line 12:
| 0x0
| 0x0
| 4
| 4
| offset (relative to .rodata)
| Signature ("NSO0")
|-
| 0x4
| 4
| size of region
|}
 
=== NSO Header ===
{| class="wikitable" border="1"
|-
! Offset
! Size
! Description
|-
| 0x0
| 4
| Magic "NSO0"
|-
|-
| 0x4
| 0x4
Line 36: Line 20:
| 0x8
| 0x8
| 4
| 4
| Reserved1
| Reserved
|-
|-
| 0xC
| 0xC
| 4
| 4
| Flags: TextCompress = 1, RoCompress = 2, DataCompress = 4, TextHash = 8, RoHash = 0x10, DataHash = 0x20
| [[#Flags|Flags]]
|-
|-
| 0x10
| 0x10
| 4
| 0x4
| TextFileOffset
| TextFileOffset
|-
|-
| 0x14
| 0x14
| 4
| 0x4
| TextMemoryOffset
| TextMemoryOffset
|-
|-
| 0x18
| 0x18
| 4
| 0x4
| TextSize
| TextSize
|-
|-
| 0x1C
| 0x1C
| 4
| 0x4
| ModuleNameOffset
| ModuleNameOffset (calculated by sizeof(header))
|-
|-
| 0x20
| 0x20
| 4
| 0x4
| RoFileOffset
| RoFileOffset
|-
|-
| 0x24
| 0x24
| 4
| 0x4
| RoMemoryOffset
| RoMemoryOffset
|-
|-
| 0x28
| 0x28
| 4
| 0x4
| RoSize
| RoSize
|-
|-
| 0x2C
| 0x2C
| 4
| 0x4
| ModuleNameSize
| ModuleNameSize
|-
|-
| 0x30
| 0x30
| 4
| 0x4
| DataFileOffset
| DataFileOffset
|-
|-
| 0x34
| 0x34
| 4
| 0x4
| DataMemoryOffset
| DataMemoryOffset
|-
|-
| 0x38
| 0x38
| 4
| 0x4
| DataSize
| DataSize
|-
|-
| 0x3C
| 0x3C
| 4
| 0x4
| BssSize
| 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
| 0x4
| TextFileSize
| TextFileSize (.text compressed size)
|-
|-
| 0x64
| 0x64
| 0x4
| 0x4
| RoFileSize
| RoFileSize (.rodata compressed size)
|-
|-
| 0x68
| 0x68
| 0x4
| 0x4
| DataFileSize
| DataFileSize (.data compressed size)
|-
| 0x6C
| 0x1C
| Reserved
|-
|-
| 0x6c
| 0x88
| 0x24
| 0x4
| Padding
| EmbeddedOffset (relative to the .rodata section)
|-
| 0x8C
| 0x4
| EmbeddedSize
|-
|-
| 0x90
| 0x90
| 8
| 0x4
| .rodata-relative extents of .dynstr
| DynStrOffset (relative to the .rodata section)
|-
| 0x94
| 0x4
| DynStrSize
|-
|-
| 0x98
| 0x98
| 8
| 0x4
| .rodata-relative extents of .dynsym
| DynSymOffset (relative to the .rodata section)
|-
| 0x9C
| 0x4
| DynSymSize
|-
|-
| 0xA0
| 0xA0
| 0x20 * 3
| 0x20
| SHA256 hashes over the decompressed sections using the above byte-sizes: .text, .rodata, and .data.
| TextHash (SHA-256 hash over the decompressed .text section using the above size)
|-
| 0xC0
| 0x20
| RoHash (SHA-256 hash over the decompressed .rodata section using the above size)
|-
| 0xE0
| 0x20
| DataHash (SHA-256 hash over the decompressed .data section using the above size)
|-
|-
| 0x100
| 0x100
|
| Variable
| Compressed sections
| Compressed sections
|}
|}


Most data in Switch binaries are standard ELF structures, however some are custom.
== Flags ==
For example, the MOD header is essentially a replacement for a PT_DYNAMIC program header.
 
=== MOD ===
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)
| zero padding
|-
| 1
| RoCompress (.rodata section is compressed)
|-
| 2
| DataCompress (.data section is compressed)
|-
|-
| 0x04
| 3
| 4
| TextHash (.text hash must be checked when loading)
| offset to magic. Always 8 (so it works when MOD is at image_base + 0).
|-
|-
| 0x08
| 4
| 4
| magic "MOD0"
| RoHash (.rodata hash must be checked when loading)
|-
|-
| 0x0C
| 5
| 4
| DataHash (.data hash must be checked when loading)
| .dynamic offset
|}
 
== ModuleId ==
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"
|-
|-
| 0x10
! Offset
| 4
! Size
| .bss start offset
! Description
|-
|-
| 0x14
| 0x0 || 0x4 || This is the total allocated space relative to argdata_addr, used for calculating the max size of the argv ptr array. Normally 0x9000?
| 4
| .bss end offset
|-
|-
| 0x18
| 0x4 || 0x4 || This is the total_bytesize of the actual argdata string.
| 4
| .eh_frame_hdr start offset
|-
|-
| 0x1C
| 0x8 || 0x18 || Unused by official sw.
| 4
| .eh_frame_hdr end offset
|-
|-
| 0x20
| 0x20 || See above || Actual argdata string.
| 4
| offset to runtime-generated module object. typically equal to .bss base.
|}
|}
* The copy of the args used with the argv array is written by official processes to actual_argdata_string+actual_argdata_size.
* argv_ptrarray written by official processes is at (args_copy+actual_argdata_size) + 0x9 & ~0x7.
Retrieved from "https://switchbrew.org/wiki/NSO"