Debugging a modded ISO

[OtakuReborn]

Hi there,

I'm in the process of modifying an ISO for Fire Emblem: Path of Radiance and I was trying to get it to run on real hardware. I am using a development build of Dolphin (5.0-12247) to verify since it raises the same error that would crash on a Wii. For what it's worth, Dolphin will continue properly after this point if I ignore the error for the session, but I do want to fix this and have some questions about the log. Specifically, the error Dolphin shows is:

Code:

58:38:087 Common\MsgHandler.cpp:115 E[MASTER]: Question: Invalid read from 0x0001bbe8, PC = 0x802342b8

For context, on the original ISO, it shows:

Code:

06:00:524 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=43a5a924, DMABuffer = 809de5c0, SrcLength = 00080000, DMALength = 00080000
06:00:524 Core\HW\DVD\FileMonitor.cpp:87 W[FileMon]:     897 kB system.cmp
06:00:797 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=43ada924, DMABuffer = 80a5e5c0, SrcLength = 0005b2c0, DMALength = 0005b2c0
06:01:000 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=43b35bdc, DMABuffer = 8116f280, SrcLength = 0004a600, DMALength = 0004a600
06:01:001 Core\HW\DVD\FileMonitor.cpp:87 W[FileMon]:     304 kB title.cmp
06:01:021 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=33a0cf34, DMABuffer = 8067d8c0, SrcLength = 000059e0, DMALength = 000059e0
06:01:021 Core\HW\DVD\FileMonitor.cpp:87 W[FileMon]:   6,732 kB Sound/gcfesnd_etc.samp

On my modified one it shows:

Code:

58:37:645 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=43a5ac90, DMABuffer = 809de320, SrcLength = 00080000, DMALength = 00080000
58:37:645 Core\HW\DVD\FileMonitor.cpp:87 W[FileMon]:     898 kB system.cmp
58:37:900 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=43adac90, DMABuffer = 80a5e320, SrcLength = 0005b560, DMALength = 0005b560
58:38:087 Common\MsgHandler.cpp:115 E[MASTER]: Question: Invalid read from 0x0001bbe8, PC = 0x802342b8

... repeated about 138 times ...

58:38:087 Common\MsgHandler.cpp:115 E[MASTER]: Question: Invalid read from 0x0001bbe8, PC = 0x802342b8
58:38:105 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=43b361f0, DMABuffer = 8116f280, SrcLength = 0004a600, DMALength = 0004a600
58:38:106 Core\HW\DVD\FileMonitor.cpp:87 W[FileMon]:     304 kB title.cmp
58:38:126 Core\HW\DVD\DVDInterface.cpp:839 I[DVD]: Read: DVDOffset=33a0d2a0, DMABuffer = 8067d8c0, SrcLength = 000059e0, DMALength = 000059e0
58:38:126 Core\HW\DVD\FileMonitor.cpp:87 W[FileMon]:   6,732 kB Sound/gcfesnd_etc.samp

I suspect the issue is that there's some aspect of the ISO format that I'm missing when I'm rebuilding it. I did modify the system.cmp file, but title.cmp should be unchanged. Files are shifted around a bit due to things being files being larger than the original. So my questions would be:

1. Is the Invalid Read error referring to loading system.cmp or title.cmp?
2. Is the repeat for 138 times a retry mechanism or is it just request to read that many times and failing?
3. Am I correct in assuming that instructions at 0x802342b8 is just for loading arbitrary data from the disc and is true for all games?
4. If it is, what does the error mean, in general?

My guess would be it has something to do with the disc sectors that I'm not really taking into account as far as the ISO is concerned, or some file alignment rules that I'm unaware of.

[JosJuice]

The "Invalid read" error refers to a RAM read, not a disc read. There can potentially be very many steps between when the game loads your modified data from the disc and when you see the "Invalid read" error, and those steps are often entirely different from game to game. So in the general case, it would be impossible for me to say things like what file the issue was caused by. But based on your log, title.cmp wasn't read until after the errors occurred, so it can't have been title.cmp (unless title.cmp also was read earlier, in a part of the log that you omitted).

As for being repeated 138 times, the game is trying to read from RAM that many times. You are running Dolphin with full MMU emulation turned off, and in this mode, the game is not notified of memory reads failing, so it would be impossible for a game to detect and retry a failed memory read. (Not that retrying a memory read makes sense for the most part.) If you want to check whether a modified ISO will work on console, I would suggest turning on full MMU emulation (in Config > Advanced) to make Dolphin behave as close to a real console as possible regarding this kind of problem.

Most likely, something is wrong with the system.cmp file. But this isn't something that I can say with certainty from just reading the logs.

[OtakuReborn]

Thanks for the response. Sounds like I’ll have to look at how I recompile the system.cmp file. At least we’ve narrowed down the problem to a single file instead of file alignment. I’ll also try turning MMU emulation on to simulate the real console.