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louise-patraandClaude Opus 5.5
43d4eebe51
Fibers may be initialized without a context and get one from _sceFiberAttachContextAndRun or _sceFiberAttachContextAndSwitch. _sceFiberInitializeWithInternalOptionImpl accepts the ulobjmgr, context size check and FPU default flags. Co-Authored-By: Claude Opus 5.5 <[email protected]>
14 lines
4.0 KiB
Markdown
14 lines
4.0 KiB
Markdown
# libSceFiber technical debt
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### Functional
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- [sceFiberGetInfo](../../../core/libs/prx/libSceFiber/Export.cpp) 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.
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### Unknown function info
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- [_sceFiberInitializeWithInternalOptionImpl](../../../core/libs/prx/libSceFiber/Export.cpp) (libSceFiber) - its signature and the flag values `0x1` (no ulobjmgr registration), `0x10` (context size check) and `0x100` (start with MXCSR `0x9fc0` and x87 control word `0x037f`) follow shadPS4's [initialize implementation](https://github.com/shadps4-emu/shadPS4/blob/f68923fe807f657348e6719ce658bcbd0a2b1c72/src/core/libraries/fiber/fiber.cpp#L150-L153) and [flags](https://github.com/shadps4-emu/shadPS4/blob/f68923fe807f657348e6719ce658bcbd0a2b1c72/src/core/libraries/fiber/fiber.h#L27-L32). Not measured on a console. `0x1` has no effect because no ulobjmgr exists; other flag bits throw. shadPS4 also sets `0x100` for `build_version` 3.50 and later in every initialize; `opt_param` and `build_version` are ignored.
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- [_sceFiberAttachContextAndRun, _sceFiberAttachContextAndSwitch](../../../core/libs/prx/libSceFiber/Export.cpp) (libSceFiber) - signatures and behaviour follow shadPS4's [run](https://github.com/shadps4-emu/shadPS4/blob/f68923fe807f657348e6719ce658bcbd0a2b1c72/src/core/libraries/fiber/fiber.cpp#L260-L261), [switch](https://github.com/shadps4-emu/shadPS4/blob/f68923fe807f657348e6719ce658bcbd0a2b1c72/src/core/libraries/fiber/fiber.cpp#L336-L337) and [attach](https://github.com/shadps4-emu/shadPS4/blob/f68923fe807f657348e6719ce658bcbd0a2b1c72/src/core/libraries/fiber/fiber.cpp#L46-L79) implementations, not measured on a console. A context is attached only to an idle fiber initialized without one; a fiber that already has a context, or is not idle, returns `SCE_FIBER_ERROR_INVALID`. A size that is not a multiple of 16 returns `SCE_FIBER_ERROR_ALIGNMENT` as in initialize, where shadPS4 returns `SCE_FIBER_ERROR_INVALID`.
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- [Fibers without a context](../../../core/libs/prx/libSceFiber/Export.cpp) (libSceFiber) - running or switching to a fiber initialized without a context, before one is attached, throws. On the console such a fiber runs on the stack of its caller, per shadPS4's [run implementation](https://github.com/shadps4-emu/shadPS4/blob/f68923fe807f657348e6719ce658bcbd0a2b1c72/src/core/libraries/fiber/fiber.cpp#L297-L313).
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- [_sceFiberGetThreadFramePointerAddress](../../../core/libs/prx/libSceFiber/Export.cpp) (libSceFiber, NID `0dy4JtMUcMQ`) forwards to `sceFiberGetThreadFramePointerAddress`; that the argument list matches is inferred from the export without the underscore, as for the underscore Ult exports, not measured
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- [Fiber stacks](../../../core/libs/prx/libSceFiber/Export.cpp) (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 (`~0xfffff` for 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
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