CRO0

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Offset Size Description
0x0 0x80 SHA-256 hash-table, verified by CRR
0x80 0x04 Magic "CRO0"
0x84 0x04 Name offset
0x88 0x04 Next loaded CRO pointer, set by RO during loading (Usually zero when the CRO is being loaded)
0x8C 0x04 Previous loaded CRO pointer, set by RO during loading
0x90 0x04 File size
0x94 0x04 .bss size
0x98 0x04 Unknown
0x9C 0x04 Unknown
0xA0 0x04 "Segment offset" that is always the same as export symbol "nnroControlObject_". 0xFFFFFFFF in CRS
0xA4 0x04 "Segment offset" for "OnLoad" function, which will be called when the module is initialized. Set to 0xFFFFFFFF if not exists.
0xA8 0x04 "Segment offset" for "OnExit" function, which will be called when the module is finalized. Set to 0xFFFFFFFF if not exists.
0xAC 0x04 "Segment offset" for "OnUnresolved" function, which will be called when an unresolved function is called. Set to 0xFFFFFFFF if not exists.
0xB0 0x04 Code offset
0xB4 0x04 Code size
0xB8 0x04 .data offset
0xBC 0x04 .data size
0xC0 0x04 Module Name offset
0xC4 0x04 Module Name size
0xC8 0x04 Segment Table offset
0xCC 0x04 Segment Table num (size = num*12)
0xD0 0x04 Named Export Table offset
0xD4 0x04 Named Export Table num (size = num * 8)
0xD8 0x04 Indexed Export Table offset
0xDC 0x04 Indexed Export Table num (size = num * 4)
0xE0 0x04 Export Strings offset
0xE4 0x04 Export Strings size
0xE8 0x04 Export Tree offset (fast lookups based on a trie-like structure)
0xEC 0x04 Export Tree num (size = num * 8)
0xF0 0x04 Import Module Table offset
0xF4 0x04 Import Module Table num (size = num * 20)
0xF8 0x04 Import Patches offset
0xFC 0x04 Import Patches num (size = num * 12)
0x100 0x04 Named Import Table offset
0x104 0x04 Named Import Table num (size = num * 8)
0x108 0x04 Indexed Import Table offset
0x10C 0x04 Indexed Import Table num (size = num * 8)
0x110 0x04 Anonymous Import Table offset
0x114 0x04 Anonymous Import Table num (size = num * 8)
0x118 0x04 Import Strings offset
0x11C 0x04 Import Strings size
0x120 0x04 unk8 offset
0x124 0x04 unk8 num
0x128 0x04 Relocation Patches offset
0x12C 0x04 Relocation Patches num (size = num * 12)
0x130 0x04 unk9 offset
0x134 0x04 unk9 num

Segment offset (4 bytes)

Bits Description
0-3 Segment index for table
4-31 Offset into segment

Segment Table entry (12 bytes)

Offset Size Description
0x0 0x4 Segment offset
0x4 0x4 Segment size
0x8 0x4 Segment id (0 = .text, 1 = .rodata, 2 = .data, 3 = .bss)

Named Export Table entry (8 bytes)

Offset Size Description
0x0 0x4 Name offset
0x4 0x4 "Segment offset" for export

Indexed Export Table entry (4 bytes)

Offset Size Description
0x0 0x4 "Segment offset" for export

Named Import Table entry (8 bytes)

Offset Size Description
0x0 0x4 Name offset
0x4 0x4 Offset of the head of a linear list that contains the patches for this import

Indexed Import Table entry (8 bytes)

Offset Size Description
0x0 0x4 index of the export symbol
0x4 0x4 Offset of the head of a linear list that contains the patches for this import

Anonymous Import Table entry (8 bytes)

Offset Size Description
0x0 0x4 "Segment offset" of the export symbol
0x4 0x4 Offset of the head of a linear list that contains the patches for this import

Import Module Table entry (20 bytes)

Offset Size Description
0x0 0x4 Module name offset
0x4 0x4 Indexed import num
0x8 0x4 Offset of the head of a sub list in Indexed Import Table
0xC 0x4 Anonymous import num
0x10 0x4 Offset of the head of a sub list in Anonymous Import Table

Patch entry (12 bytes)

Offset Size Description
0x0 0x4 "Segment offset" for output.
0x4 0x1 Patch type (0=nothing/ignore, 2=38=write u32 absolute (base+addend), 3=write u32 relative (base+addend-in_ptr), 10=THUMB branch, 28=ARM32 branch, 29=modify ARM32 branch offset, 42=write u32 relative (((signed int)base*2)/2+addend-in_ptr), otherwise err) (This is apparently a subset of relocation type for ARM ELF)
0x5 0x1 For import patches, non-zero if last entry; for relocation patches, this is the referred segment index
0x6 0x1 For import patches, 1 is written to first entry if all symbols loaded successfully; unknown (padding?) for relocation patches
0x7 0x1 Unknown (padding?)
0x8 0x4 addend

ARM32 branch instruction is constructed as follows:

 If addend > 0x2000000 or addend < 0xFE000000, then skip.
 If (addend&1) == 1 then write "b +4" (nop).
 Else write as normal.

CRO with extension .cro is used for "DLLs". CRS with extension .crs is in the same format of CRO but storing the symbol information of the static module (the main application). The end of the file is aligned to a 0x1000-byte boundary with 0xCC bytes.

The first hash-table entry hashes the 0x100-byte header following the hash-table. The following hash-table entries hash the sections specified in the header.

When the RO module loads the entire CRO into process memory(mapped in the 0x00100000-0x04000000 region), it modifies the mapped CRO data. The magic field is also changed to "FIXD" if fix level is not 0.

Upon loading, the RO module will look for export symbol "nnroAeabiAtexit_" to patch it to its import symbol "__aeabi_atexit".

For dumping symbols and loading a CRO into IDA, see [1] and [2].