On Tue, Oct 18, 2022 at 06:04:56PM +0800, WANG Xuerui wrote: > From: WANG Xuerui <git@xxxxxxxxxx> > What description? > diff --git a/Documentation/loongarch/syscall-abi.rst b/Documentation/loongarch/syscall-abi.rst > new file mode 100644 > index 000000000000..6f63aa3cfc64 > --- /dev/null > +++ b/Documentation/loongarch/syscall-abi.rst > @@ -0,0 +1,36 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +=============================== > +Linux/LoongArch system call ABI > +=============================== > + > +This document describes the system call ABI of Linux/LoongArch. > +As the kernel is 64-bit only for now, the description below assumes an LP64\* > +calling convention. > + > +Syscall numbers and parameters > +============================== > + > +Like with other recent architecture ports, for the most part Linux/LoongArch > +reuses the asm-generic syscall numbers and parameters. > +There are a few points worth mentioning though. > + > +* There is no ``renameat``. Use ``renameat2`` instead. > +* There is no ``getrlimit`` or ``setrlimit``. Use ``prlimit64`` instead. > +* There is no ``fstat`` or ``newfstatat``. Only ``statx`` is provided, and > + low-level components making their own syscalls are expected to be aware of > + this (and provide their own shims if necessary). > + > +Invocation > +========== > + > +System calls are currently made with the ``syscall 0`` instruction. > +Although the immediate field in the instruction is not checked at present, > +it is strongly advised to keep it zeroed in case it is to be made meaningful > +in the future. > + > +The system call number is placed in the register ``a7``. > +Parameters, if present, are placed from ``a0`` through ``a6`` as needed, > +as if calling a function with the respective arguments. > +Upon return, ``a0`` contains the return value, and ``t0-t8`` should be > +considered clobbered; all other registers are preserved. The wording can be improved: ---- >8 ---- diff --git a/Documentation/loongarch/syscall-abi.rst b/Documentation/loongarch/syscall-abi.rst index 6f63aa3cfc64e5..d05fa2e0211bbf 100644 --- a/Documentation/loongarch/syscall-abi.rst +++ b/Documentation/loongarch/syscall-abi.rst @@ -5,32 +5,32 @@ Linux/LoongArch system call ABI =============================== This document describes the system call ABI of Linux/LoongArch. -As the kernel is 64-bit only for now, the description below assumes an LP64\* -calling convention. +As the kernel currently only supports 64-bit LoongArch architecture, the +description below assumes LP64\* calling convention. Syscall numbers and parameters ============================== -Like with other recent architecture ports, for the most part Linux/LoongArch +Like ther recent architecture ports, for the most part Linux/LoongArch reuses the asm-generic syscall numbers and parameters. -There are a few points worth mentioning though. +There are a few limitations worth mentioning though. * There is no ``renameat``. Use ``renameat2`` instead. * There is no ``getrlimit`` or ``setrlimit``. Use ``prlimit64`` instead. -* There is no ``fstat`` or ``newfstatat``. Only ``statx`` is provided, and - low-level components making their own syscalls are expected to be aware of - this (and provide their own shims if necessary). +* There is no ``fstat`` or ``newfstatat``. Only ``statx`` is provided and + low-level components invoking their own syscalls are expected to be aware + of this (and provide their own shims if necessary). Invocation ========== -System calls are currently made with the ``syscall 0`` instruction. +System calls are currently invoked with the ``syscall 0`` instruction. Although the immediate field in the instruction is not checked at present, -it is strongly advised to keep it zeroed in case it is to be made meaningful +it is strongly advised to keep it zeroed in case the field has purposes in the future. -The system call number is placed in the register ``a7``. -Parameters, if present, are placed from ``a0`` through ``a6`` as needed, -as if calling a function with the respective arguments. -Upon return, ``a0`` contains the return value, and ``t0-t8`` should be -considered clobbered; all other registers are preserved. +The system call number is placed in the register ``a7``. Parameters, if +present, are placed from ``a0`` through ``a6`` as needed, as if calling +a function with respective arguments. Upon return, the return value is placed +in ``a0`` and ``t0-t8`` should be considered clobbered; all other registers +are preserved. Thanks. -- An old man doll... just what I always wanted! - Clara
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