Alexandros Mandravillis
1.8 KiB
ExitCriticalSection register contract
psx_syscall handles BIOS SYS(02h) directly, including when optional BIOS HLE
services are disabled. It enables the current interrupt bit and the hardware
interrupt mask in COP0 SR. It preserves the caller's general registers.
In particular, it must not assign a return value to v0.
An SDK wrapper can call another BIOS service, then ExitCriticalSection, and
return the earlier result. Clearing v0 turns a successful operation into a
false failure. This can prevent a caller from entering its video decode loop
even though disc streaming and audio have already started.
The hardware contract is documented in
PSX-SPX, SYS(02h).
The specification allows K0 to change; this direct handler preserves it too.
The host-only cpu->pc = 0 continuation and C return value remain unchanged.
exit_critical_section_test compiles the real traps.c implementation with
LTO and tests 16 combinations of incoming v0 and SR. It checks the full CPU
state, allowing only the documented SR update and host continuation change.
The test uses no BIOS, generated retail code, or game data.
The fixture links only the real trap unit and its test driver. It relies on interprocedural optimization removing syscall paths that the driver never calls, rather than providing fake scheduler or exception implementations. This link contract is verified with Windows x64 MinGW GCC 16.1.0 and is enabled only for that toolchain. Other configurations still register the test, but CTest reports it as Skipped with the unsupported compiler and reason. They do not provide register-preservation coverage until the fixture's link contract is validated there or a portable real-dependency harness replaces it.