AGC: an indirect indexed draw binds its whole INDEX_BUFFER_SIZE range, so Guardians of the Galaxy (PPSA01748) stops when the title declares 0x10000000 indices over a 54 MiB buffer ("guest memory is not readable") #6526

Guardians of the Galaxy stops during its first level load, with music already playing. It issues a DRAW_INDEX_INDIRECT_MULTI after setting INDEX_BUFFER_SIZE to 0x10000000 (16-bit indices, so 512 MiB). For indirect indexed draws, resolveIndirectDraw binds that whole declared range and CheckRange requires all of it to be readable. Only the first ~54 MiB behind the index base is mapped, so the draw fails:

[videoout] presentation failed: AGC driver: guest memory is not readable at 0x386590000 (range 0x383240000+0x20000000)
terminate called after throwing an instance of 'std::runtime_error'
  what():  AGC driver: guest memory is not readable at 0x386590000 (range 0x383240000+0x20000000)

Title: Marvel's Guardians of the Galaxy (PPSA01748 v01.006.000)
Where it stops: the level-1 load, a few minutes after START GAME, on main 03c4cb5e7 plus #6232. #6232 is needed to get past the #6191 stop, which comes earlier on plain main. Linux, RTX 4090. 5 of 5 runs, at the same range each time; the first unreadable page is 0x386590000 (once 0x3865a0000).

What the draw is

A local print before the CheckRange in resolveIndirectDraw (not pushed):

indirect indexed draw: opcode 0x38 INDEX_BUFFER_SIZE 0x10000000 indexType 0 indexBase 0x383240000 records 144 stride 20 args 0x2d18b91d4
packet 10 words: c0083800 00000004 00000090 00000280 40000280 00000090 ...

A native stack from the throw: Driver::draw → Pm4::ResolveDraw (the indirect branch, inlined) → GuestMemory::CheckRange → require.

So the 512 MiB is not a size the title reads. It's the declared upper bound, which the CP uses to clamp firstIndex + indexCount per record. The 144 records, 20 bytes each, are the usual (count, instances, first index, base vertex, first instance) and select ranges inside it. On the console, index fetches past those ranges never happen, so the unmapped tail doesn't matter. Here the driver needs the tail to be readable because it binds the declared range as the index buffer (Pm4.cpp: "the declared range is the hardware's view of the index buffer, so that is what gets bound").

Possible directions (not tried)

• Bind the readable prefix of the declared range, from the index base to the first unreadable page. Records that reach past it would read past the end of what is mapped on the console too.
• Or bind the union of the records' ranges, clamped to INDEX_BUFFER_SIZE, when the records are CPU-visible at packet time. That doesn't work if the GPU writes the records, which is usual for indirect draws, so the first option looks safer.

I haven't picked one or written a fix. I can run either on the title the same day.

Tested and written by Claude (AI assistant) on a contributor's machine.