D154 - The ranked list is the wrong view at a wall; the ordered tail is the right one

decided · 2026-08-20

A ranked list of imports answers "what does this guest spend its time on", which is the right question for choosing what to implement next. At a wall it is the wrong question entirely, and it cannot be made into the right one by making it longer.

sceKernelDirectMemoryQuery at 99.9% of calls tells you nothing about a guest that just wrote through a null pointer. The only useful question there is what did it call last, and a frequency ranking cannot answer that at any length.

The ordering was always recorded - the dispatcher has filled a ring of (sequence, index, arg0) since it existed, sized at 8192 while no run has exceeded 400. It simply never left the process. The trace persisted the aggregate and dropped the sequence.

So CallTrace now carries the last 48 calls in order, and the run report prints them when

• and only when - there was a fault. Consecutive repeats are collapsed, because a guest clearing memory calls memset three hundred times in a row and printing them individually buries the two calls either side that matter.

It paid for itself immediately. The first run with it produced:

sceKernelAllocateMainDirectMemory(0x1fe0000)
printf(...)
memset(0x0) x3

A guest asking for memory, being refused, printing an error, and clearing a buffer it never got. That is sceKernelAllocateMainDirectMemory identified as a blocker, its argument order established (the first argument is a length in both observed calls), and the failure mode explained - from one view of data that had been collected all along.

arg0 is kept alongside the label for the same reason, and earns it in the same trace: libSceVideoOut::0xb9b56b04b654a0ac(0x7fff0001) is a guest passing GuestError::Unimplemented back to us as a video-output handle. That is D125's failure caught live rather than inferred from a fault address.

The general shape: the data was already there. What was missing was a view of it that matched the question being asked. Worth remembering the next time something looks like it needs new instrumentation.