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Date: Sun, 15 May 2022 17:47:04 +0800
From: WANG Xuerui <kernel@...0n.name>
To: Huacai Chen <chenhuacai@...il.com>, WANG Xuerui <kernel@...0n.name>
Cc: Huacai Chen <chenhuacai@...ngson.cn>,
Arnd Bergmann <arnd@...db.de>,
Andy Lutomirski <luto@...nel.org>,
Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
David Airlie <airlied@...ux.ie>,
Jonathan Corbet <corbet@....net>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-arch <linux-arch@...r.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Xuefeng Li <lixuefeng@...ngson.cn>,
Yanteng Si <siyanteng@...ngson.cn>,
Guo Ren <guoren@...nel.org>,
Jiaxun Yang <jiaxun.yang@...goat.com>,
Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH V10 13/22] LoongArch: Add system call support
On 5/14/22 22:39, Huacai Chen wrote:
> Hi, Xuerui,
>
> On Sat, May 14, 2022 at 9:53 PM WANG Xuerui <kernel@...0n.name> wrote:
>> Hi,
>>
>> On 5/14/22 16:03, Huacai Chen wrote:
>>> Add system call support and related uaccess.h for LoongArch.
>>>
>>> Q: Why keep _ARCH_WANT_SYS_CLONE definition while there is clone3:
>>> A: The latest glibc release (2.35) has some basic support for clone3 but
>>> it isn't complete. E.g., pthread_create() and spawni() have converted
>>> to use clone3 but fork() will still use clone. Moreover, some seccomp
>>> related applications can still not work perfectly with clone3. E.g.,
>>> Chromium sandbox cannot work at all and there is no solution for it,
>>> which is more terrible than the fork() story [1].
>>>
>>> [1] https://chromium-review.googlesource.com/c/chromium/src/+/2936184
>>>
>>> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
>>> ---
>>> arch/loongarch/include/asm/seccomp.h | 20 ++
>>> arch/loongarch/include/asm/syscall.h | 74 +++++++
>>> arch/loongarch/include/asm/uaccess.h | 269 +++++++++++++++++++++++
>>> arch/loongarch/include/asm/unistd.h | 11 +
>>> arch/loongarch/include/uapi/asm/unistd.h | 5 +
>>> arch/loongarch/kernel/entry.S | 89 ++++++++
>>> arch/loongarch/kernel/syscall.c | 63 ++++++
>>> 7 files changed, 531 insertions(+)
>>> create mode 100644 arch/loongarch/include/asm/seccomp.h
>>> create mode 100644 arch/loongarch/include/asm/syscall.h
>>> create mode 100644 arch/loongarch/include/asm/uaccess.h
>>> create mode 100644 arch/loongarch/include/asm/unistd.h
>>> create mode 100644 arch/loongarch/include/uapi/asm/unistd.h
>>> create mode 100644 arch/loongarch/kernel/entry.S
>>> create mode 100644 arch/loongarch/kernel/syscall.c
>>>
>>> diff --git a/arch/loongarch/include/asm/seccomp.h b/arch/loongarch/include/asm/seccomp.h
>>> new file mode 100644
>>> index 000000000000..31d6ab42e43e
>>> --- /dev/null
>>> +++ b/arch/loongarch/include/asm/seccomp.h
>>> @@ -0,0 +1,20 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +
>>> +#ifndef _ASM_SECCOMP_H
>>> +#define _ASM_SECCOMP_H
>>> +
>>> +#include <asm/unistd.h>
>>> +
>>> +#include <asm-generic/seccomp.h>
>>> +
>>> +#ifdef CONFIG_32BIT
>>> +# define SECCOMP_ARCH_NATIVE AUDIT_ARCH_LOONGARCH32
>>> +# define SECCOMP_ARCH_NATIVE_NR NR_syscalls
>>> +# define SECCOMP_ARCH_NATIVE_NAME "loongarch32"
>>> +#else
>>> +# define SECCOMP_ARCH_NATIVE AUDIT_ARCH_LOONGARCH64
>>> +# define SECCOMP_ARCH_NATIVE_NR NR_syscalls
>>> +# define SECCOMP_ARCH_NATIVE_NAME "loongarch64"
>>> +#endif
>>> +
>>> +#endif /* _ASM_SECCOMP_H */
>>> diff --git a/arch/loongarch/include/asm/syscall.h b/arch/loongarch/include/asm/syscall.h
>>> new file mode 100644
>>> index 000000000000..e286dc58476e
>>> --- /dev/null
>>> +++ b/arch/loongarch/include/asm/syscall.h
>>> @@ -0,0 +1,74 @@
>>> +/* SPDX-License-Identifier: GPL-2.0+ */
>>> +/*
>>> + * Author: Hanlu Li <lihanlu@...ngson.cn>
>>> + * Huacai Chen <chenhuacai@...ngson.cn>
>>> + *
>>> + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
>>> + */
>>> +
>>> +#ifndef __ASM_LOONGARCH_SYSCALL_H
>>> +#define __ASM_LOONGARCH_SYSCALL_H
>>> +
>>> +#include <linux/compiler.h>
>>> +#include <uapi/linux/audit.h>
>>> +#include <linux/elf-em.h>
>>> +#include <linux/kernel.h>
>>> +#include <linux/sched.h>
>>> +#include <linux/uaccess.h>
>>> +#include <asm/ptrace.h>
>>> +#include <asm/unistd.h>
>>> +
>>> +extern void *sys_call_table[];
>>> +
>>> +static inline long syscall_get_nr(struct task_struct *task,
>>> + struct pt_regs *regs)
>>> +{
>>> + return regs->regs[11];
>> It may be better readability-wise to somehow change this 11 to something
>> resembling A7, but it's okay as-is.
> OK, keep it as is.
>
>>> +}
>>> +
>>> +static inline void syscall_rollback(struct task_struct *task,
>>> + struct pt_regs *regs)
>>> +{
>>> + regs->regs[4] = regs->orig_a0;
>>> +}
>>> +
>>> +static inline long syscall_get_error(struct task_struct *task,
>>> + struct pt_regs *regs)
>>> +{
>>> + unsigned long error = regs->regs[4];
>>> +
>>> + return IS_ERR_VALUE(error) ? error : 0;
>>> +}
>>> +
>>> +static inline long syscall_get_return_value(struct task_struct *task,
>>> + struct pt_regs *regs)
>>> +{
>>> + return regs->regs[4];
>>> +}
>>> +
>>> +static inline void syscall_set_return_value(struct task_struct *task,
>>> + struct pt_regs *regs,
>>> + int error, long val)
>>> +{
>>> + regs->regs[4] = (long) error ? error : val;
>>> +}
>>> +
>>> +static inline void syscall_get_arguments(struct task_struct *task,
>>> + struct pt_regs *regs,
>>> + unsigned long *args)
>>> +{
>>> + args[0] = regs->orig_a0;
>>> + memcpy(&args[1], ®s->regs[5], 5 * sizeof(long));
>>> +}
>>> +
>>> +static inline int syscall_get_arch(struct task_struct *task)
>>> +{
>>> + return AUDIT_ARCH_LOONGARCH64;
>>> +}
>>> +
>>> +static inline bool arch_syscall_is_vdso_sigreturn(struct pt_regs *regs)
>>> +{
>>> + return false;
>>> +}
>>> +
>>> +#endif /* __ASM_LOONGARCH_SYSCALL_H */
>>> diff --git a/arch/loongarch/include/asm/uaccess.h b/arch/loongarch/include/asm/uaccess.h
>>> new file mode 100644
>>> index 000000000000..217c6a3727b1
>>> --- /dev/null
>>> +++ b/arch/loongarch/include/asm/uaccess.h
>>> @@ -0,0 +1,269 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +/*
>>> + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
>>> + *
>>> + * Derived from MIPS:
>>> + * Copyright (C) 1996, 1997, 1998, 1999, 2000, 03, 04 by Ralf Baechle
>>> + * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
>>> + * Copyright (C) 2007 Maciej W. Rozycki
>>> + * Copyright (C) 2014, Imagination Technologies Ltd.
>>> + */
>>> +#ifndef _ASM_UACCESS_H
>>> +#define _ASM_UACCESS_H
>>> +
>>> +#include <linux/kernel.h>
>>> +#include <linux/string.h>
>>> +#include <linux/extable.h>
>>> +#include <asm/pgtable.h>
>>> +#include <asm-generic/extable.h>
>>> +#include <asm-generic/access_ok.h>
>>> +
>>> +extern u64 __ua_limit;
>>> +
>>> +#define __UA_ADDR ".dword"
>>> +#define __UA_LA "la.abs"
>>> +#define __UA_LIMIT __ua_limit
>>> +
>>> +/*
>>> + * get_user: - Get a simple variable from user space.
>>> + * @x: Variable to store result.
>>> + * @ptr: Source address, in user space.
>>> + *
>>> + * Context: User context only. This function may sleep if pagefaults are
>>> + * enabled.
>>> + *
>>> + * This macro copies a single simple variable from user space to kernel
>>> + * space. It supports simple types like char and int, but not larger
>>> + * data types like structures or arrays.
>>> + *
>>> + * @ptr must have pointer-to-simple-variable type, and the result of
>>> + * dereferencing @ptr must be assignable to @x without a cast.
>>> + *
>>> + * Returns zero on success, or -EFAULT on error.
>>> + * On error, the variable @x is set to zero.
>>> + */
>>> +#define get_user(x, ptr) \
>>> +({ \
>>> + const __typeof__(*(ptr)) __user *__p = (ptr); \
>>> + \
>>> + might_fault(); \
>>> + access_ok(__p, sizeof(*__p)) ? __get_user((x), __p) : \
>>> + ((x) = 0, -EFAULT); \
>>> +})
>>> +
>>> +/*
>>> + * put_user: - Write a simple value into user space.
>>> + * @x: Value to copy to user space.
>>> + * @ptr: Destination address, in user space.
>>> + *
>>> + * Context: User context only. This function may sleep if pagefaults are
>>> + * enabled.
>>> + *
>>> + * This macro copies a single simple value from kernel space to user
>>> + * space. It supports simple types like char and int, but not larger
>>> + * data types like structures or arrays.
>>> + *
>>> + * @ptr must have pointer-to-simple-variable type, and @x must be assignable
>>> + * to the result of dereferencing @ptr.
>>> + *
>>> + * Returns zero on success, or -EFAULT on error.
>>> + */
>>> +#define put_user(x, ptr) \
>>> +({ \
>>> + __typeof__(*(ptr)) __user *__p = (ptr); \
>>> + \
>>> + might_fault(); \
>>> + access_ok(__p, sizeof(*__p)) ? __put_user((x), __p) : -EFAULT; \
>>> +})
>>> +
>>> +/*
>>> + * __get_user: - Get a simple variable from user space, with less checking.
>>> + * @x: Variable to store result.
>>> + * @ptr: Source address, in user space.
>>> + *
>>> + * Context: User context only. This function may sleep if pagefaults are
>>> + * enabled.
>>> + *
>>> + * This macro copies a single simple variable from user space to kernel
>>> + * space. It supports simple types like char and int, but not larger
>>> + * data types like structures or arrays.
>>> + *
>>> + * @ptr must have pointer-to-simple-variable type, and the result of
>>> + * dereferencing @ptr must be assignable to @x without a cast.
>>> + *
>>> + * Caller must check the pointer with access_ok() before calling this
>>> + * function.
>>> + *
>>> + * Returns zero on success, or -EFAULT on error.
>>> + * On error, the variable @x is set to zero.
>>> + */
>>> +#define __get_user(x, ptr) \
>>> +({ \
>>> + int __gu_err = 0; \
>>> + \
>>> + __chk_user_ptr(ptr); \
>>> + __get_user_common((x), sizeof(*(ptr)), ptr); \
>>> + __gu_err; \
>>> +})
>>> +
>>> +/*
>>> + * __put_user: - Write a simple value into user space, with less checking.
>>> + * @x: Value to copy to user space.
>>> + * @ptr: Destination address, in user space.
>>> + *
>>> + * Context: User context only. This function may sleep if pagefaults are
>>> + * enabled.
>>> + *
>>> + * This macro copies a single simple value from kernel space to user
>>> + * space. It supports simple types like char and int, but not larger
>>> + * data types like structures or arrays.
>>> + *
>>> + * @ptr must have pointer-to-simple-variable type, and @x must be assignable
>>> + * to the result of dereferencing @ptr.
>>> + *
>>> + * Caller must check the pointer with access_ok() before calling this
>>> + * function.
>>> + *
>>> + * Returns zero on success, or -EFAULT on error.
>>> + */
>>> +#define __put_user(x, ptr) \
>>> +({ \
>>> + int __pu_err = 0; \
>>> + __typeof__(*(ptr)) __pu_val; \
>>> + \
>>> + __pu_val = (x); \
>>> + __chk_user_ptr(ptr); \
>>> + __put_user_common(ptr, sizeof(*(ptr))); \
>>> + __pu_err; \
>>> +})
>>> +
>>> +struct __large_struct { unsigned long buf[100]; };
>>> +#define __m(x) (*(struct __large_struct __user *)(x))
>>> +
>>> +#define __get_user_common(val, size, ptr) \
>>> +do { \
>>> + switch (size) { \
>>> + case 1: __get_data_asm(val, "ld.b", ptr); break; \
>>> + case 2: __get_data_asm(val, "ld.h", ptr); break; \
>>> + case 4: __get_data_asm(val, "ld.w", ptr); break; \
>>> + case 8: __get_data_asm(val, "ld.d", ptr); break; \
>>> + default: BUILD_BUG(); break; \
>>> + } \
>>> +} while (0)
>>> +
>>> +#define __get_kernel_common(val, size, ptr) __get_user_common(val, size, ptr)
>>> +
>>> +#define __get_data_asm(val, insn, ptr) \
>>> +{ \
>>> + long __gu_tmp; \
>>> + \
>>> + __asm__ __volatile__( \
>>> + "1: " insn " %1, %2 \n" \
>>> + "2: \n" \
>>> + " .section .fixup,\"ax\" \n" \
>>> + "3: li.w %0, %3 \n" \
>>> + " or %1, $r0, $r0 \n" \
>>> + " b 2b \n" \
>>> + " .previous \n" \
>>> + " .section __ex_table,\"a\" \n" \
>>> + " "__UA_ADDR "\t1b, 3b \n" \
>>> + " .previous \n" \
>>> + : "+r" (__gu_err), "=r" (__gu_tmp) \
>>> + : "m" (__m(ptr)), "i" (-EFAULT)); \
>>> + \
>>> + (val) = (__typeof__(*(ptr))) __gu_tmp; \
>>> +}
>>> +
>>> +#define __put_user_common(ptr, size) \
>>> +do { \
>>> + switch (size) { \
>>> + case 1: __put_data_asm("st.b", ptr); break; \
>>> + case 2: __put_data_asm("st.h", ptr); break; \
>>> + case 4: __put_data_asm("st.w", ptr); break; \
>>> + case 8: __put_data_asm("st.d", ptr); break; \
>>> + default: BUILD_BUG(); break; \
>>> + } \
>>> +} while (0)
>>> +
>>> +#define __put_kernel_common(ptr, size) __put_user_common(ptr, size)
>>> +
>>> +#define __put_data_asm(insn, ptr) \
>>> +{ \
>>> + __asm__ __volatile__( \
>>> + "1: " insn " %z2, %1 # __put_user_asm\n" \
>>> + "2: \n" \
>>> + " .section .fixup,\"ax\" \n" \
>>> + "3: li.w %0, %3 \n" \
>>> + " b 2b \n" \
>>> + " .previous \n" \
>>> + " .section __ex_table,\"a\" \n" \
>>> + " " __UA_ADDR " 1b, 3b \n" \
>>> + " .previous \n" \
>>> + : "+r" (__pu_err), "=m" (__m(ptr)) \
>>> + : "Jr" (__pu_val), "i" (-EFAULT)); \
>>> +}
>>> +
>>> +#define __get_kernel_nofault(dst, src, type, err_label) \
>>> +do { \
>>> + int __gu_err = 0; \
>>> + \
>>> + __get_kernel_common(*((type *)(dst)), sizeof(type), \
>>> + (__force type *)(src)); \
>>> + if (unlikely(__gu_err)) \
>>> + goto err_label; \
>>> +} while (0)
>>> +
>>> +#define __put_kernel_nofault(dst, src, type, err_label) \
>>> +do { \
>>> + type __pu_val; \
>>> + int __pu_err = 0; \
>>> + \
>>> + __pu_val = *(__force type *)(src); \
>>> + __put_kernel_common(((type *)(dst)), sizeof(type)); \
>>> + if (unlikely(__pu_err)) \
>>> + goto err_label; \
>>> +} while (0)
>>> +
>>> +extern unsigned long __copy_user(void *to, const void *from, __kernel_size_t n);
>>> +
>>> +static inline unsigned long __must_check
>>> +raw_copy_from_user(void *to, const void __user *from, unsigned long n)
>>> +{
>>> + return __copy_user(to, from, n);
>>> +}
>>> +
>>> +static inline unsigned long __must_check
>>> +raw_copy_to_user(void __user *to, const void *from, unsigned long n)
>>> +{
>>> + return __copy_user(to, from, n);
>>> +}
>>> +
>>> +#define INLINE_COPY_FROM_USER
>>> +#define INLINE_COPY_TO_USER
>>> +
>>> +/*
>>> + * __clear_user: - Zero a block of memory in user space, with less checking.
>>> + * @addr: Destination address, in user space.
>>> + * @size: Number of bytes to zero.
>>> + *
>>> + * Zero a block of memory in user space. Caller must check
>>> + * the specified block with access_ok() before calling this function.
>>> + *
>>> + * Returns number of bytes that could not be cleared.
>>> + * On success, this will be zero.
>>> + */
>>> +extern unsigned long __clear_user(void __user *addr, __kernel_size_t size);
>>> +
>>> +#define clear_user(addr, n) \
>>> +({ \
>>> + void __user *__cl_addr = (addr); \
>>> + unsigned long __cl_size = (n); \
>>> + if (__cl_size && access_ok(__cl_addr, __cl_size)) \
>>> + __cl_size = __clear_user(__cl_addr, __cl_size); \
>>> + __cl_size; \
>>> +})
>>> +
>>> +extern long strncpy_from_user(char *to, const char __user *from, long n);
>>> +extern long strnlen_user(const char __user *str, long n);
>>> +
>>> +#endif /* _ASM_UACCESS_H */
>>> diff --git a/arch/loongarch/include/asm/unistd.h b/arch/loongarch/include/asm/unistd.h
>>> new file mode 100644
>>> index 000000000000..cfddb0116a8c
>>> --- /dev/null
>>> +++ b/arch/loongarch/include/asm/unistd.h
>>> @@ -0,0 +1,11 @@
>>> +/* SPDX-License-Identifier: GPL-2.0+ */
>>> +/*
>>> + * Author: Hanlu Li <lihanlu@...ngson.cn>
>>> + * Huacai Chen <chenhuacai@...ngson.cn>
>>> + *
>>> + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
>>> + */
>>> +
>>> +#include <uapi/asm/unistd.h>
>>> +
>>> +#define NR_syscalls (__NR_syscalls)
>>> diff --git a/arch/loongarch/include/uapi/asm/unistd.h b/arch/loongarch/include/uapi/asm/unistd.h
>>> new file mode 100644
>>> index 000000000000..fcb668984f03
>>> --- /dev/null
>>> +++ b/arch/loongarch/include/uapi/asm/unistd.h
>>> @@ -0,0 +1,5 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>>> +#define __ARCH_WANT_SYS_CLONE
>>> +#define __ARCH_WANT_SYS_CLONE3
>> Having read the discussion in v9 regarding the sandbox scenario, I agree
>> leaving clone alone would probably be the better choice. It's relieving
>> seeing the stat cruft dropped... World rebuilds of new-world distros
>> pending on the horizon. :-D
> clone3() is not just a beautiful version of clone(), it has some new
> features such as pidfd, so we need both clone() and clone3().
Apologizes if I didn't make it clear, but to clear any confusion: I'm
not saying we don't want clone3, and we should keep both clone (for not
breaking end user workflows involving sandboxed processes such as
browsers) and clone3 (the path forward).
>
>>> +
>>> +#include <asm-generic/unistd.h>
>>> diff --git a/arch/loongarch/kernel/entry.S b/arch/loongarch/kernel/entry.S
>>> new file mode 100644
>>> index 000000000000..d5b3dbcf5425
>>> --- /dev/null
>>> +++ b/arch/loongarch/kernel/entry.S
>>> @@ -0,0 +1,89 @@
>>> +/* SPDX-License-Identifier: GPL-2.0 */
>>> +/*
>>> + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
>>> + *
>>> + * Derived from MIPS:
>>> + * Copyright (C) 1994 - 2000, 2001, 2003 Ralf Baechle
>>> + * Copyright (C) 1999, 2000 Silicon Graphics, Inc.
>>> + * Copyright (C) 2001 MIPS Technologies, Inc.
>>> + */
>>> +
>>> +#include <asm/asm.h>
>>> +#include <asm/asmmacro.h>
>>> +#include <asm/loongarch.h>
>>> +#include <asm/regdef.h>
>>> +#include <asm/stackframe.h>
>>> +#include <asm/thread_info.h>
>>> +
>>> + .text
>>> + .cfi_sections .debug_frame
>>> + .align 5
>>> +SYM_FUNC_START(handle_syscall)
>>> + csrrd t0, PERCPU_BASE_KS
>>> + la.abs t1, kernelsp
>>> + add.d t1, t1, t0
>>> + move t2, sp
>>> + ld.d sp, t1, 0
>>> +
>>> + addi.d sp, sp, -PT_SIZE
>>> + cfi_st t2, PT_R3
>>> + cfi_rel_offset sp, PT_R3
>>> + st.d zero, sp, PT_R0
>>> + csrrd t2, LOONGARCH_CSR_PRMD
>>> + st.d t2, sp, PT_PRMD
>>> + csrrd t2, LOONGARCH_CSR_CRMD
>>> + st.d t2, sp, PT_CRMD
>>> + csrrd t2, LOONGARCH_CSR_EUEN
>>> + st.d t2, sp, PT_EUEN
>>> + csrrd t2, LOONGARCH_CSR_ECFG
>>> + st.d t2, sp, PT_ECFG
>>> + csrrd t2, LOONGARCH_CSR_ESTAT
>>> + st.d t2, sp, PT_ESTAT
>>> + cfi_st ra, PT_R1
>>> + cfi_st a0, PT_R4
>>> + cfi_st a1, PT_R5
>>> + cfi_st a2, PT_R6
>>> + cfi_st a3, PT_R7
>>> + cfi_st a4, PT_R8
>>> + cfi_st a5, PT_R9
>>> + cfi_st a6, PT_R10
>>> + cfi_st a7, PT_R11
>>> + csrrd ra, LOONGARCH_CSR_ERA
>>> + st.d ra, sp, PT_ERA
>>> + cfi_rel_offset ra, PT_ERA
>>> +
>>> + cfi_st tp, PT_R2
>>> + cfi_st u0, PT_R21
>>> + cfi_st fp, PT_R22
>>> +
>>> + SAVE_STATIC
>>> +
>>> + move u0, t0
>>> + li.d tp, ~_THREAD_MASK
>>> + and tp, tp, sp
>>> +
>>> + move a0, sp
>>> + bl do_syscall
>>> +
>>> + RESTORE_ALL_AND_RET
>>> +SYM_FUNC_END(handle_syscall)
>>> +
>>> +SYM_CODE_START(ret_from_fork)
>>> + bl schedule_tail # a0 = struct task_struct *prev
>>> + move a0, sp
>>> + bl syscall_exit_to_user_mode
>>> + RESTORE_STATIC
>>> + RESTORE_SOME
>>> + RESTORE_SP_AND_RET
>>> +SYM_CODE_END(ret_from_fork)
>>> +
>>> +SYM_CODE_START(ret_from_kernel_thread)
>>> + bl schedule_tail # a0 = struct task_struct *prev
>>> + move a0, s1
>>> + jirl ra, s0, 0
>>> + move a0, sp
>>> + bl syscall_exit_to_user_mode
>>> + RESTORE_STATIC
>>> + RESTORE_SOME
>>> + RESTORE_SP_AND_RET
>>> +SYM_CODE_END(ret_from_kernel_thread)
>>> diff --git a/arch/loongarch/kernel/syscall.c b/arch/loongarch/kernel/syscall.c
>>> new file mode 100644
>>> index 000000000000..3fc4211db989
>>> --- /dev/null
>>> +++ b/arch/loongarch/kernel/syscall.c
>>> @@ -0,0 +1,63 @@
>>> +// SPDX-License-Identifier: GPL-2.0+
>>> +/*
>>> + * Author: Hanlu Li <lihanlu@...ngson.cn>
>>> + * Huacai Chen <chenhuacai@...ngson.cn>
>>> + *
>>> + * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
>>> + */
>>> +#include <linux/capability.h>
>>> +#include <linux/entry-common.h>
>>> +#include <linux/errno.h>
>>> +#include <linux/linkage.h>
>>> +#include <linux/syscalls.h>
>>> +#include <linux/unistd.h>
>>> +
>>> +#include <asm/asm.h>
>>> +#include <asm/signal.h>
>>> +#include <asm/switch_to.h>
>>> +#include <asm-generic/syscalls.h>
>>> +
>>> +#undef __SYSCALL
>>> +#define __SYSCALL(nr, call) [nr] = (call),
>>> +
>>> +SYSCALL_DEFINE6(mmap, unsigned long, addr, unsigned long, len, unsigned long,
>>> + prot, unsigned long, flags, unsigned long, fd, off_t, offset)
>>> +{
>>> + if (offset & ~PAGE_MASK)
>>> + return -EINVAL;
>>> +
>>> + return ksys_mmap_pgoff(addr, len, prot, flags, fd, offset >> PAGE_SHIFT);
>>> +}
>>> +
>>> +void *sys_call_table[__NR_syscalls] = {
>>> + [0 ... __NR_syscalls - 1] = sys_ni_syscall,
>>> +#include <asm/unistd.h>
>>> +};
>>> +
>>> +typedef long (*sys_call_fn)(unsigned long, unsigned long,
>>> + unsigned long, unsigned long, unsigned long, unsigned long);
>>> +
>>> +void noinstr do_syscall(struct pt_regs *regs)
>>> +{
>>> + unsigned long nr;
>>> + sys_call_fn syscall_fn;
>>> +
>>> + nr = regs->regs[11];
>>> + /* Set for syscall restarting */
>>> + if (nr < NR_syscalls)
>>> + regs->regs[0] = nr + 1;
>>> +
>>> + regs->csr_era += 4;
>>> + regs->orig_a0 = regs->regs[4];
>>> + regs->regs[4] = -ENOSYS;
>>> +
>>> + nr = syscall_enter_from_user_mode(regs, nr);
>>> +
>>> + if (nr < NR_syscalls) {
>> I saw in the manual that there's the BADI (出错指令) CSR that records the
>> faulting instruction word for exceptions other than INT, GCHC and MERR;
>> this implies we can read the trapping syscall insn word from this CSR,
>> to inspect its immediate field, so we can reserve non-zero immediates on
>> the syscall insn for future use.
>>
>> This would take 3 insns to complete: csrrd, bitfield extraction, and
>> bail if non-zero; this should be an acceptable tradeoff for a lot of
>> extensibility and scalability?
> This need much efforts, we can optimize it in future.
Fair point. No one has used syscall insns with non-zero immediates, at
least from what I've seen during the year porting software and reviewing
others' patches, so we could add the check later and breakage should
only be theoretical.
>
> Huacai
>>> + syscall_fn = sys_call_table[nr];
>>> + regs->regs[4] = syscall_fn(regs->orig_a0, regs->regs[5], regs->regs[6],
>>> + regs->regs[7], regs->regs[8], regs->regs[9]);
>>> + }
>>> +
>>> + syscall_exit_to_user_mode(regs);
>>> +}
Now that we've gone through every point:
Reviewed-by: WANG Xuerui <git@...0n.name>
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