anders429 / mgba_log Goto Github PK

If logging is done both during normal execution and during interrupts, interrupt logs will overwrite data already present in the log buffer. This causes data loss, and is an improper use of the unsafe code.

I've been able to reproduce this quite simply, and I'll add the test binary to the integration test suite when I have a fix for this. The basic idea is to repeatedly write "Hello, world!" to debug logs, and then configure interrupts to write a log message "in irq" whenever an interrupt occurs. The result looks something like this:

...
[INFO] GBA Debug:	Hello, world!
[DEBUG] GBA Debug:	in irq world
[INFO] GBA Debug:	
[INFO] GBA Debug:	Hello, world!
...
[INFO] GBA Debug:	Hello, world!
[DEBUG] GBA Debug:	in irq w
[INFO] GBA Debug:	
[INFO] GBA Debug:	Hello, world!
...

The "in irq" message overwrites the beginning of the already written "Hello, world!" message, and then flushes the buffer. Then the writing of the original message resumes, but since the beginning of the buffer is never re-written, the rest of the data is lost due to the first byte being null.

Note that log deliberately designed the Log trait to be shared among multiple contexts. It is therefore necessary to ensure that this implementation can be shared among both normal code and interrupt handlers.