LoongArch: Add system call support

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 has some basic support for clone3 but it is
   not 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

Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

1 files changed, 63 insertions, 0 deletions

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@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.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) {
+		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);
+}