The syscall entry points to the kernel defined by SYSCALL_DEFINEx() and COMPAT_SYSCALL_DEFINEx() should only be called from userspace through kernel entry points, but not from the kernel itself. This will allow cleanups and optimizations to the entry paths *and* to the parts of the kernel code which currently need to pretend to be userspace in order to make use of syscalls.
Signed-off-by: Dominik Brodowski <li...@dominikbrodowski.net> --- Documentation/process/adding-syscalls.rst | 14 -------------- include/linux/syscalls.h | 7 +++++++ 2 files changed, 7 insertions(+), 14 deletions(-) diff --git a/Documentation/process/adding-syscalls.rst b/Documentation/process/adding-syscalls.rst index 8cc25a06f353..35a14b730da9 100644 --- a/Documentation/process/adding-syscalls.rst +++ b/Documentation/process/adding-syscalls.rst @@ -201,12 +201,6 @@ followed by the (type, name) pairs for the parameters as arguments. Using this macro allows metadata about the new system call to be made available for other tools. -The new entry point also needs a corresponding function prototype, in -``include/linux/syscalls.h``, marked as asmlinkage to match the way that system -calls are invoked:: - - asmlinkage long sys_xyzzy(...); - Some architectures (e.g. x86) have their own architecture-specific syscall tables, but several other architectures share a generic syscall table. Add your new system call to the generic list by adding an entry to the list in @@ -240,7 +234,6 @@ To summarize, you need a commit that includes: - ``CONFIG`` option for the new function, normally in ``init/Kconfig`` - ``SYSCALL_DEFINEn(xyzzy, ...)`` for the entry point - - corresponding prototype in ``include/linux/syscalls.h`` - generic table entry in ``include/uapi/asm-generic/unistd.h`` - fallback stub in ``kernel/sys_ni.c`` @@ -302,12 +295,6 @@ needed to deal with them. (Typically, the ``compat_sys_`` version converts the values to 64-bit versions and either calls on to the ``sys_`` version, or both of them call a common inner implementation function.) -The compat entry point also needs a corresponding function prototype, in -``include/linux/compat.h``, marked as asmlinkage to match the way that system -calls are invoked:: - - asmlinkage long compat_sys_xyzzy(...); - If the system call involves a structure that is laid out differently on 32-bit and 64-bit systems, say ``struct xyzzy_args``, then the include/linux/compat.h header file should also include a compat version of the structure (``struct @@ -344,7 +331,6 @@ version; the entry in ``include/uapi/asm-generic/unistd.h`` should use To summarize, you need: - a ``COMPAT_SYSCALL_DEFINEn(xyzzy, ...)`` for the compat entry point - - corresponding prototype in ``include/linux/compat.h`` - (if needed) 32-bit mapping struct in ``include/linux/compat.h`` - instance of ``__SC_COMP`` not ``__SYSCALL`` in ``include/uapi/asm-generic/unistd.h`` diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index a78186d826d7..700a83a9c1ad 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -941,4 +941,11 @@ asmlinkage long sys_pkey_free(int pkey); asmlinkage long sys_statx(int dfd, const char __user *path, unsigned flags, unsigned mask, struct statx __user *buffer); + +/* + * The kernel should not use call syscalls (i.e., sys_xyzyyz()) directly. + * Instead, use one of the following functions which work equivalent to + * the syscall they are named for. + */ + #endif -- 2.16.2