D895 - A 2D array access to a one-layer image reaches layer zero

Status: decided Date: 2026-10-19

A compute program may fetch from or store to an image through the 2D_ARRAY dimensionality, taking the layer from the address element after its two coordinates and any level from the one after that. The translation addresses the image as the two-dimensional one it is, at the coordinates given. Layer zero is the image. Any other layer is out of bounds, as it is on the hardware for a one-layer view: a fetch there reads zero, and a store there writes nothing.

The host binds such an image only where its descriptor views one layer, the first: DEPTH and BASE_ARRAY (SQ_IMG_RSRC_WORD4, bits 0-12 and 16-28, gfx10-rsrc.json) both zero. The type may be 2D or 2D_ARRAY. A view of more layers, or of a later one, is refused by name.

A program may rewrite a table-loaded descriptor's TYPE field (SQ_IMG_RSRC_WORD3 bits 31:28) to 2D or 2D_ARRAY through a scratch register that nothing else reads: s_and_b32 t, sW, 0x0fffffff then s_or_b32 sW, t, type << 28. That pair translates to nothing, and the descriptor still names the image it was loaded as. A rewrite of any other bit is refused, since it would name another image.

Why: Grand Theft Auto V's compute copy loads two image descriptors and rewrites their type to 2D_ARRAY (s_or_b32 s23, vcc_lo, 0xd0000000) before it fetches from one and stores to the other, its layer taken from its user data. The images it copies are two-dimensional, so the layer it names is the first. A device test copies through a 2D-array access at layer zero, and at layer one the destination keeps every texel.

Rejected:

• Binding every image a 2D-array access reaches as a host 2D array of its layers: the images this meets have one layer, and a layered surface's slices are placed by addrlib's slice pitch, which is read only when a program needs more than one.