LoongArch: Add signal handling support

Add ucontext/sigcontext definition and signal handling support for
LoongArch.

Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/uapi/asm/sigcontext.h

+/* SPDX-License-Identifier: GPL-2.0+ WITH Linux-syscall-note */
+/*
+ * Author: Hanlu Li <lihanlu@loongson.cn>
+ *         Huacai Chen <chenhuacai@loongson.cn>
+ *
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _UAPI_ASM_SIGCONTEXT_H
+#define _UAPI_ASM_SIGCONTEXT_H
+
+#include <linux/types.h>
+#include <linux/posix_types.h>
+
+/* FP context was used */
+#define SC_USED_FP		(1 << 0)
+/* Address error was due to memory load */
+#define SC_ADDRERR_RD		(1 << 30)
+/* Address error was due to memory store */
+#define SC_ADDRERR_WR		(1 << 31)
+
+struct sigcontext {
+	__u64	sc_pc;
+	__u64	sc_regs[32];
+	__u32	sc_flags;
+	__u64	sc_extcontext[0] __attribute__((__aligned__(16)));
+};
+
+#define CONTEXT_INFO_ALIGN	16
+struct sctx_info {
+	__u32	magic;
+	__u32	size;
+	__u64	padding;	/* padding to 16 bytes */
+};
+
+/* FPU context */
+#define FPU_CTX_MAGIC		0x46505501
+#define FPU_CTX_ALIGN		8
+struct fpu_context {
+	__u64	regs[32];
+	__u64	fcc;
+	__u32	fcsr;
+};
+
+#endif /* _UAPI_ASM_SIGCONTEXT_H */

arch/loongarch/include/uapi/asm/signal.h

+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+/*
+ * Copyright (C) 2020-2022 Loongson Technology Corporation Limited
+ */
+#ifndef _UAPI_ASM_SIGNAL_H
+#define _UAPI_ASM_SIGNAL_H
+
+#define MINSIGSTKSZ 4096
+#define SIGSTKSZ    16384
+
+#include <asm-generic/signal.h>
+
+#endif

arch/loongarch/include/uapi/asm/ucontext.h

+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __LOONGARCH_UAPI_ASM_UCONTEXT_H
+#define __LOONGARCH_UAPI_ASM_UCONTEXT_H
+
+/**
+ * struct ucontext - user context structure
+ * @uc_flags:
+ * @uc_link:
+ * @uc_stack:
+ * @uc_mcontext:	holds basic processor state
+ * @uc_sigmask:
+ * @uc_extcontext:	holds extended processor state
+ */
+struct ucontext {
+	unsigned long		uc_flags;
+	struct ucontext		*uc_link;
+	stack_t			uc_stack;
+	sigset_t		uc_sigmask;
+	/* There's some padding here to allow sigset_t to be expanded in the
+	 * future.  Though this is unlikely, other architectures put uc_sigmask
+	 * at the end of this structure and explicitly state it can be
+	 * expanded, so we didn't want to box ourselves in here. */
+	__u8		  __unused[1024 / 8 - sizeof(sigset_t)];
+	/* We can't put uc_sigmask at the end of this structure because we need
+	 * to be able to expand sigcontext in the future.  For example, the
+	 * vector ISA extension will almost certainly add ISA state.  We want
+	 * to ensure all user-visible ISA state can be saved and restored via a
+	 * ucontext, so we're putting this at the end in order to allow for
+	 * infinite extensibility.  Since we know this will be extended and we
+	 * assume sigset_t won't be extended an extreme amount, we're
+	 * prioritizing this. */
+	struct sigcontext	uc_mcontext;
+};
+
+#endif /* __LOONGARCH_UAPI_ASM_UCONTEXT_H */