Good News for the DS port

Last week, I restructured the DS loader to use a SeekableReadStream for file reading. Once that was in place and working, I restructured the PS2 loader to use a SeekableReadStream as well and tested it (this needed to be done anyway and it helped me ensure there was nothing inherently wrong with the way I was using SeekableReadStream in the DS loader).

I then had problems reading the symbol table in successfully. After some wasted time :P, I realized it was just a silly mistake. I had neglected to initialize _symtab_sect to anything in dsloader.h and the value of uninitialized ints is undefined in C++. Thus, the loader was detecting, from the value that _symtab_sect had, that the symbol table was already read in when it wasn't.

At this point the loader was getting to the point where I had to deal with the relocations. I used consolePrintfs to make sure that the relocation types the loader was detecting were the same as the ones detected by arm-eabi-objdump (they were). I then began coding for these relocations. After a day of work on the relocations with no success as far as getting games to run with dynamic plugins enabled on the DS, I decided to disable the thumb-interworking on the ds temporarily so I could work on getting the DS with plugins in a runnable state without having to deal with the complication of thumb instructions/relocations.

I worked further on the relocations yesterday; I started dumping the instructions to be relocated and immediately noticed a MAJOR problem. Every instruction was 0x00000000! The addresses of the instructions seemed reasonable, though, so I suspected it had something to do with how the plugins were being built and not how I was retrieving target addresses. I dumped Mapfiles with "-Map" during plugin linking and discovered that whole input sections were being discarded, among other problems. After switching out the linker script for a modified version of the default "arm-eabi-ld" linker script, these problems seemed to be fixed, perhaps because the modified linker script I was using (based on the script used by the main executable) used the MEMORY command to map out different blocks of memory but I was trying to force the start address of the ".text" section to be 0. I am not sure whether switching out this linker script will cause problems.

I then did a fair bit of reading on the ARM instruction set and continued tweaking/testing the relocation code. Things still weren't working like they should have. Yotam suggested comparing completely unrelocated code and semi-relocated code to see what ld was already doing for me, and through a few dumps, I realized I was trying to do A LOT that ld already did redundantly and thus messing up things that were already fixed! After removing this redundant code, I got Beneath a Steel Sky to run successfully with Dynamic Plugins enabled on the DS!

My next order of business, then, is to test the rest of the engines (some of which have relocation types I still haven't dealt with). Then, I'll reintegrate the thumb-interworking and deal with any major complications that brings (if any :D).

~Tony

Also, I plan to update my wiki schedule shortly: http://wiki.scummvm.org/index.php/User:Toneman