mirror of
https://github.com/boykopovar/AnyPS5.git
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David
e44e828f61
The fchdir entry still said FreeBSD's search-permission check was not
modelled, although it has run on Linux since 0e4d94ce3 and now runs on
every host but Windows.
16 lines
8.2 KiB
Markdown
16 lines
8.2 KiB
Markdown
# libkernel_sys technical debt
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### Functional
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- [fchdir](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) changes the guest working directory to the descriptor's directory: on Windows through the path recorded when the descriptor was opened, on Linux through the `/proc/self/fd` link target. It returns `EBADF` for a descriptor that is not open and `ENOTDIR` for one that is not a directory. Outside Windows it checks search permission on the directory with `faccessat`, which fails with `EACCES` as FreeBSD `change_dir` does; on Windows that check is not modelled. A directory renamed after it was opened is still reached through the recorded path. Console behaviour is unverified
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- [openat](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) passes `AT_FDCWD` (-100) and absolute paths to `open`. Any other relative path is joined to the descriptor's host directory, found the same way as for `fchdir`, so guest path aliases and case-insensitive name matching do not apply to it, and a `..` component is not kept inside the guest root. It returns `EBADF` for a descriptor that is not open and `ENOTDIR` for one that is not a directory. As with `open`, `O_NOFOLLOW` and `O_NONBLOCK` are ignored. PPSA99003 opens directory entries this way. Console behaviour is unverified
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- [fchmodat](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) passes `AT_FDCWD` (-100) and absolute paths to `chmod`; any other relative path is joined to the descriptor's host directory the same way as for `openat`, so guest path aliases and case-insensitive name matching do not apply to it and a `..` component is not kept inside the guest root. A flag other than `0` or `AT_SYMLINK_NOFOLLOW` (0x200) returns `EINVAL`; the mode is masked to `07777`. With `AT_SYMLINK_NOFOLLOW` a symbolic link throws, since the host cannot change a link's own mode, while a regular file is changed either way. The mode maps to the host file mode, which on Windows is only the CRT's read-only bit. PPSA99621 calls it through `std::filesystem::permissions`. Console behaviour is unverified
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- [pathconf](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) looks the path up as FreeBSD 11's `kern_pathconf` does (links followed, `ENAMETOOLONG` for a path of 1024 bytes or more or a component over 255) and returns the constants of FreeBSD 11's UFS `ufs_pathconf` for files and directories alike: `_PC_LINK_MAX` 32767, `_PC_NAME_MAX` 255, `_PC_PATH_MAX` and `_PC_SYMLINK_MAX` 1024, `_PC_PIPE_BUF` 512, `_PC_CHOWN_RESTRICTED` and `_PC_NO_TRUNC` 1, `_PC_FILESIZEBITS` 64, `_PC_REC_MAX_XFER_SIZE` -1, `_PC_PRIO_IO` and `_PC_SYNC_IO` 0. Whether the console's filesystems report the same is not verified. It throws for the names whose UFS value depends on the mount (`_PC_ALLOC_SIZE_MIN`, `_PC_REC_INCR_XFER_SIZE`, `_PC_REC_MIN_XFER_SIZE`, `_PC_MIN_HOLE_SIZE`), the kernel options (`_PC_ACL_EXTENDED`, `_PC_ACL_PATH_MAX`, `_PC_ACL_NFS4`, `_PC_MAC_PRESENT`) or the page size (`_PC_REC_XFER_ALIGN`), and on which UFS and `vop_stdpathconf` disagree (`_PC_MAX_CANON`, `_PC_MAX_INPUT`, `_PC_VDISABLE`, `_PC_ASYNC_IO`); other names fail with `EINVAL`
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- [mkdirat](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) passes `AT_FDCWD` (-100) and absolute paths to `mkdir`. Any other relative path is joined to the descriptor's host directory, found the same way as for `fchdir`, so guest path aliases and case-insensitive name matching do not apply to it, and a `..` component is not kept inside the guest root. It returns `EBADF` for a descriptor that is not open and `ENOTDIR` for one that is not a directory. On Windows, `mode` is ignored. Console behaviour is unverified
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- [readlink](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) on Windows reads a symbolic link's target from its reparse data and returns it with `/` separators, only when the target is relative, as `symlink` creates them. A symbolic link with an absolute target and a junction throw, as a host path has no guest form. Any other reparse point throws too, where FreeBSD reports `EINVAL` for a file that is not a link
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- [readlinkat](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) passes `AT_FDCWD` (-100) and absolute paths to `readlink`. Any other relative path is joined to the descriptor's host directory, found the same way as for `fchdir`, so guest path aliases and case-insensitive name matching do not apply to it, and a `..` component is not kept inside the guest root. It returns `EBADF` for a descriptor that is not open and `ENOTDIR` for one that is not a directory. Console behaviour is unverified
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- [unlinkat](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) passes `AT_FDCWD` (-100) and absolute paths to `rmdir` (with `AT_REMOVEDIR`, 0x800) or `unlink`. Any other relative path is joined to the descriptor's host directory, found the same way as for `fchdir`, so guest path aliases and case-insensitive name matching do not apply to it, and a `..` component is not kept inside the guest root. It returns `EBADF` for a descriptor that is not open and `ENOTDIR` for one that is not a directory. Removing a directory without `AT_REMOVEDIR` fails with `EPERM`, removing `.` or `..` with `AT_REMOVEDIR` fails with `EINVAL`, and flags other than `AT_REMOVEDIR` fail with `EINVAL`. Console behaviour is unverified
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- [renameat](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) passes `AT_FDCWD` (-100) and absolute paths to `rename`. Any other relative path is joined to its descriptor's host directory, found the same way as for `fchdir`, so guest path aliases and case-insensitive name matching do not apply to relative descriptors, and a `..` component is not kept inside the guest root. It returns `EBADF` for a descriptor that is not open and `ENOTDIR` for one that is not a directory. Console behaviour is unverified
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- [fork](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) throws: creating a child process is not supported. PPSA19111 imports it and fails to load without it. Its engine calls `fork` in `Posix_Daemonize`, only with `-daemonize`, and in `Platform_ShellExecute` before `execvp("xdg-open")`, which the main menu's Previews button reaches, so pressing Previews ends in this throw. [setsid](../../../core/libs/prx/libkernel_sys/Export.cpp) fails with `EPERM`, as FreeBSD's does for a process group leader, since the guest is taken to lead its own process group (see `kill`). [umask](../../../core/libs/prx/libkernel_sys/Export.cpp) keeps the guest's mask (initially 022, masked to 07777) and returns the previous one, Linux named shared-memory creation applies it, but ordinary files are still created with the host process's mask
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- [chroot](../../../core/libs/prx/libkernel_sys/Export.cpp) (libkernel_sys) follows FreeBSD 11.4's [`sys_chroot`](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/sys/kern/vfs_syscalls.c#L776-L807) and [`pwd_chroot`](https://github.com/freebsd/freebsd-src/blob/8c639945a44588f6cfdddfb057bb5aad88735da0/sys/kern/kern_descrip.c#L3059-L3085) for a root caller: `EFAULT` for a null path, `ENOENT` for an empty or missing one, `ENAMETOOLONG` for a path of 1024 bytes or more or a component over 255, and `ENOTDIR` for a path that is not a directory or passes through a file. A directory that is the guest root (`/`, `/..`, or `.` after `fchdir` to a descriptor of `/`) succeeds and changes nothing, as the root stays the same directory; the guest is taken never to have changed its root, so open directory descriptors do not make it fail with `EPERM` (`kern.chroot_allow_open_directories` 1). Any other directory throws, naming the path: the guest path resolver has a fixed root and mount aliases (`/app0`, `/savedata0`) that do not move with it. On the console a title starts in a sandbox root, where `pwd_chroot` refuses with `EPERM` while a directory is open; whether that holds for titles, and whether a title holds `PRIV_VFS_CHROOT`, are unverified. Porpoise (PPSA99764) weak-imports it and calls it only as `fchdir` to its saved descriptor of `/` then `chroot(".")`, to put its sandbox root back after a jailbreak daemon replaced it ([`put_root_back`](https://github.com/elripalda/Porpoise-Dolphin-Emulator-for-PS5/blob/2ed1ab5a06995aa198f7bccd4da0f90c3fc29d39/src/porpoise_jailbreak.cpp#L303-L331))
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