CRO0

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].

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.

---