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XairRrR
9206b5ae4b
Since 794714983 every fiber ran on an mmap'd host stack so that host calls
cannot overrun the small contexts PPSA01341 packs next to each other. A
title that derives state from the stack pointer then reads the wrong
memory: PPSA05684's job fibers have 512 KiB contexts at 1 MiB-aligned
addresses and find their job record by masking rsp with ~0xfffff, so the
job system lost track of a GameInit job and the game waited forever
right after loading big4r/actor76.txt. Its 64 KiB fibers fault later on
a host stack too.
A fiber now gets a host stack only when its context is smaller than
64 KiB; a larger context is the stack again, as on the console. The
limit sits between the 16 KiB contexts that need protection and the
64 KiB ones that need the guest stack (technical debt entry). The fiber
test runs a 512 KiB fiber and checks that its stack is in its context;
it fails without this change.
AI-assisted: yes
1.9 KiB
1.9 KiB
libSceFiber technical debt
Functional
- sceFiberGetInfo reports the requested-size window at the top of the host stack used for execution, rather than the original caller buffer, which is retained and pinned. The additional 1 MiB host-call margin below that window is not included in
size_context. Planet Coaster (PPSA01736 v01.017) uses this range for ChakraCore garbage-collector stack scans; reporting the unused caller buffer makes the scan cross unmapped memory. The range is covered by a regression test while running, switching and migrating a fiber between threads. Console behavior for substituted host stacks has no direct equivalent and is not measured.
Unknown function info
- _sceFiberGetThreadFramePointerAddress (libSceFiber, NID
0dy4JtMUcMQ) forwards tosceFiberGetThreadFramePointerAddress; that the argument list matches is inferred from the export without the underscore, as for the underscore Ult exports, not measured - Fiber stacks (libSceFiber) - a fiber whose context is smaller than 64 KiB runs on an mmap'd host stack of its context size plus 1 MiB, so host calls made from it (21 KiB deep when PPSA01341 reaches SPIRV-Tools from a 16 KiB context) do not overwrite the contexts packed next to it; a larger context is the stack, as on the console. PPSA05684 needs the second: its job fibers have 64 KiB and 512 KiB contexts, the 512 KiB ones at 1 MiB-aligned addresses, and find their job record by masking the stack pointer (
~0xffffffor the 512 KiB ones), which a host stack breaks (the game waits forever in GameInit, or faults later in a 64 KiB fiber). The 64 KiB limit is chosen between these two titles, not measured: a title with small contexts that also derives state from the stack pointer, or one whose host calls exceed what is left of a large context, is not covered