=> patch the gb_postproc() function to add the 48 bytes nintendo logo data as required to run the ROM on an actual unit. This is documented in the GB Pandocs and observable for anyone who has access to a programmable cart.
This wasn't implemented as of http://sourceforge.net/projects/sdcc/files/snapshot_builds/sdcc-src/sdcc-src-20120323-7479.tar.bz2/download
0104-0133 - Nintendo Logo
These bytes define the bitmap of the Nintendo logo that is displayed when the gameboy gets turned on. The hexdump of this bitmap is:
CE ED 66 66 CC 0D 00 0B 03 73 00 83 00 0C 00 0D
00 08 11 1F 88 89 00 0E DC CC 6E E6 DD DD D9 99
BB BB 67 63 6E 0E EC CC DD DC 99 9F BB B9 33 3E
The gameboys boot procedure verifies the content of this bitmap (after it has displayed it), and LOCKS ITSELF UP if these bytes are incorrect. A CGB verifies only the first 18h bytes of the bitmap, but others (for example a pocket gameboy) verify all 30h bytes.