Merge pull request #6750 from LeandroLP23/docs/debt-thread-priority-gap

docs(debt): record that guest thread priorities are not applied to host threads

docs/dev/debt/libkernel.md

@@ -98,7 +98,6 @@
 - [uDGXwUKqi8s](../../../core/libs/prx/libkernel/Unimplemented.cpp) (libkernel) - unknown name, signature
 - [sceKernelGetCpuTemperature, sceKernelGetSocSensorTemperature](../../../core/libs/prx/libkernel/System/src/ThermalSensors.cpp) (libkernel) - read the host's thermal sensors: on Linux from `/sys/class/hwmon` and `/sys/class/thermal`, on Windows from the ACPI thermal zones (`MSAcpi_ThermalZoneTemperature` over WMI) and the storage temperature property of the first physical drive. Sensor 0 is the CPU/package value, 1 the first other value and 2 an NVMe value; a host that exposes none reports every sensor as unsupported (`EINVAL`). The console's SoC channel count and meanings are hardware-dependent and differ from the host's, the host sensors are not the console's, the ACPI reading is unavailable on many machines, and the storage temperature property is numbered 52 on Windows 10 2004 and later and 22 before it, so the mapping, the values and the unsupported-input error are unverified; the storage channel was checked against the drive's own SMART composite temperature on one NVMe host (`StorageDeviceTemperatureProperty`, 36 °C on a WD_BLACK SN7100). `sceKernelGetCpuTemperature` reports sensor 0. PPSA99058 and PPSA99420 call both
 - [LinuxProtFromSce](../../../core/libs/prx/libkernel/DirectMemory/DirectMemory.cpp) (libkernel) - protection bits 0x100 and 0x200 are accepted and assumed not to affect host CPU access; host protection is derived only from the read, write and execute bits
-- [sched_get_priority_max, sched_get_priority_min](../../../core/libs/prx/libkernel/System/src/Process.cpp) (libkernel) - measured on a PS5 (firmware 13.60): `SCHED_FIFO` (1) and `SCHED_RR` (3) report a maximum of 767 and a minimum of 256, and every other policy, `SCHED_OTHER` (2) included, returns -1 with `EINVAL`. `pthread_setschedparam` and `scePthreadSetschedparam` accept those two policies with a priority of 256 to 767 or 896 to 959 and keep the policy, as measured; a created thread takes the policy and priority of explicit scheduling attributes, or its creator's when it inherits, as it does with a null attribute
 - [inet_pton, inet_ntop](../../../core/libs/prx/libkernel/Socket/src/AddressConversion.cpp) (libkernel) - the text forms are assumed to be those of FreeBSD 11.4 and are unverified on a console: `inet_pton` accepts only four decimal parts without leading zeros for `AF_INET` and the RFC 4291 forms for `AF_INET6` (one `::` standing for at least one group, a dotted-quad tail only as the last 32 bits, no zone id), and `inet_ntop` prints lowercase hex with the first longest run of two or more zero groups compressed, and a dotted tail only for `::a.b.c.d` and `::ffff:a.b.c.d`. They no longer depend on the host resolver library
 - [sceKernelIsThreadSanitizerEnabled](../../../core/libs/prx/libkernel/System/src/Sanitizer.cpp) (libkernel, NID `LzoM-wVLJDE`) - no source gives the signature; `int (void)` is assumed from `sceKernelIsAddressSanitizerEnabled` and from PPSA23226's bundled `libSceJobManager_nosubmission.prx`, which passes no arguments and tests only the 32-bit result
 - [getdtablesize](../../../core/libs/prx/libkernel/System/src/Process.cpp) (libkernel) - throws: FreeBSD returns the smaller of the `RLIMIT_NOFILE` soft limit and `maxfilesperproc` ([`sys_getdtablesize`](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/sys/kern/kern_descrip.c#L338-L355)), and neither value is known for the console, where `getrlimit(RLIMIT_NOFILE)` throws too. VLC (PPSA85300) imports it for a `closefrom` loop in the child of its spawn helper ([libc_stubs.c](https://github.com/ZiZc3/VLC/blob/d46be6a68f4244466b041c2dc1b640915ac1a983/ps5/compat/libc_stubs.c#L66-L72)), which never runs because its `fork` fails with `ENOSYS`
@@ -106,6 +105,7 @@
 
 ### Functional
 
+- [Guest thread scheduling](../../../core/libs/prx/libkernel/Pthread/src/Thread.cpp) (libkernel) - the policies and priorities that `sched_get_priority_max`, `sched_get_priority_min`, `pthread_setschedparam` and `scePthreadSetschedparam` accept, and those a created thread takes, follow a PS5 (firmware 13.60), but they are only recorded and reported: they are not applied to host threads, so a title's priority order has no effect on host scheduling
 - [sceKernelMprotect, sceKernelMtypeprotect](../../../core/libs/prx/libkernel/DirectMemory/DirectMemory.cpp) (libkernel) over a range with a gap that is not registered in the allocation tracker protect the registered parts and skip the gap, and return 0, as FreeBSD 11.4's [`vm_map_protect`](https://github.com/freebsd/freebsd-src/blob/release/11.4.0/sys/vm/vm_map.c) does (it has no check for holes); a range whose start is unmapped (also when later pages are mapped) returns `SCE_KERNEL_ERROR_EINVAL` (`mprotect`: `EINVAL`) because an existing test pins that for an unmapped start; FreeBSD answers 0 there too (`vm_map_protect` takes the next entry), so this errno is not taken from the source and was not changed. `sceKernelMprotect` threw for a gap before, which ended the title. Every part is checked for a GPU or image pin before the first one is protected; the parts are then protected one after the other, so a host protection failure in a later part leaves the earlier parts changed (FreeBSD's `vm_map_protect` cannot fail in its second pass). The behaviour on the console is not known. None of this was measured on a console.
 - [sceKernelMprotect protection bits](../../../core/libs/prx/libkernel/DirectMemory/Export.cpp) (libkernel) - bits outside `0x3F7` are dropped instead of refused, as FreeBSD 11's [`sys_mprotect`](https://github.com/freebsd/freebsd-src/blob/34bd34750187bae02a0086402c78c031c59dd8b3/sys/vm/vm_mmap.c#L606) does with `VM_PROT_ALL`. Onimusha: Way of the Sword (PPSA27836 01.000.001) maps direct memory with `0xf2` and then protects it with `0xfffffff2`. Not measured on a console; the map calls and `sceKernelMtypeprotect` still refuse undefined bits
 - [JIT shared memory](../../../core/libs/prx/libkernel/DirectMemory/Jit.cpp) (libkernel) - `sceKernelJitCreateSharedMemory`, `sceKernelJitCreateAliasOfSharedMemory` and `sceKernelJitMapSharedMemory` take the signatures of [Orbital](https://github.com/AlexAltea/orbital)'s `tools/ida/db_types.json` (name, length, maximum protection, descriptor out; descriptor, maximum protection, descriptor out; descriptor, protection, address in and out), which ps4sdk, ps5-jar-loader and the call sites in RetroArch PPSA99169, XPSemu PPSA97358 and VLC PPSA85300 match; SharpProspero declares the alias as returning the descriptor. The object is a host anonymous file shared by its descriptors (a `memfd` on Linux, a delete-on-close temporary file mapped as an executable section on Windows), the alias is a duplicate descriptor, and every map maps the whole object, so writes through one view show through the others; a non-null address is a hint, as in `mmap` without `MAP_FIXED`. Not measured on the console: a length that is zero or not a multiple of 16 KiB and protection bits other than CPU read, write and execute are `EINVAL`; an alias or a map asking for more than the descriptor's maximum protection (write and execute counting as read) is `EACCES`, as FreeBSD 11's `vm_map_protect` treats a protection past `max_protection`; a descriptor that is not a JIT object is `EBADF`. The name is ignored, the objects do not count against the flexible memory budget, `mprotect` of a view is not limited to the maximum protection, and `mmap` of the descriptors is unsupported, as for `shm_open`. On Linux the `memfd` is created without `MFD_EXEC`, which Linux 6.3 added and older kernels reject with `EINVAL`, and relies on the protection of the mapping: the flag only sets the file's execute permission bits, and the direct memory `memfd` is mapped executable the same way; a host with `vm.memfd_noexec` set to 2 refuses the creation and the call throws