arch/riscv/kernel/traps.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2012 Regents of the University of California
  */

 #include <linux/cpu.h>
 #include <linux/kernel.h>
 #include <linux/init.h>
 #include <linux/randomize_kstack.h>
 #include <linux/sched.h>
 #include <linux/sched/debug.h>
 #include <linux/sched/signal.h>
 #include <linux/signal.h>
 #include <linux/kdebug.h>
 #include <linux/uaccess.h>
 #include <linux/kprobes.h>
 #include <linux/uprobes.h>
 #include <asm/uprobes.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/irq.h>
 #include <linux/kexec.h>
 #include <linux/entry-common.h>

 #include <asm/asm-prototypes.h>
 #include <asm/bug.h>
 #include <asm/cfi.h>
 #include <asm/csr.h>
 #include <asm/processor.h>
 #include <asm/ptrace.h>
 #include <asm/syscall.h>
 #include <asm/thread_info.h>
 #include <asm/vector.h>
 #include <asm/irq_stack.h>

 int show_unhandled_signals = 1;

 static DEFINE_SPINLOCK(die_lock);

 static int copy_code(struct pt_regs *regs, u16 *val, const u16 *insns)
 {
 	const void __user *uaddr = (__force const void __user *)insns;

 	if (!user_mode(regs))
 		return get_kernel_nofault(*val, insns);

 	/* The user space code from other tasks cannot be accessed. */
 	if (regs != task_pt_regs(current))
 		return -EPERM;

 	return copy_from_user_nofault(val, uaddr, sizeof(*val));
 }

 static void dump_instr(const char *loglvl, struct pt_regs *regs)
 {
 	char str[sizeof("0000 ") * 12 + 2 + 1], *p = str;
 	const u16 *insns = (u16 *)instruction_pointer(regs);
 	long bad;
 	u16 val;
 	int i;

 	for (i = -10; i < 2; i++) {
 		bad = copy_code(regs, &val, &insns[i]);
 		if (!bad) {
 			p += sprintf(p, i == 0 ? "(%04hx) " : "%04hx ", val);
 		} else {
 			printk("%sCode: Unable to access instruction at 0x%px.\n",
 			       loglvl, &insns[i]);
 			return;
 		}
 	}
 	printk("%sCode: %s\n", loglvl, str);
 }

 void die(struct pt_regs *regs, const char *str)
 {
 	static int die_counter;
 	int ret;
 	long cause;
 	unsigned long flags;

 	oops_enter();

 	spin_lock_irqsave(&die_lock, flags);
 	console_verbose();
 	bust_spinlocks(1);

 	pr_emerg("%s [#%d]\n", str, ++die_counter);
 	print_modules();
 	if (regs) {
 		show_regs(regs);
 		dump_instr(KERN_EMERG, regs);
 	}

 	cause = regs ? regs->cause : -1;
 	ret = notify_die(DIE_OOPS, str, regs, 0, cause, SIGSEGV);

 	if (kexec_should_crash(current))
 		crash_kexec(regs);

 	bust_spinlocks(0);
 	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
 	spin_unlock_irqrestore(&die_lock, flags);
 	oops_exit();

 	if (in_interrupt())
 		panic("Fatal exception in interrupt");
 	if (panic_on_oops)
 		panic("Fatal exception");
 	if (ret != NOTIFY_STOP)
 		make_task_dead(SIGSEGV);
 }

 void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr)
 {
 	struct task_struct *tsk = current;

 	if (show_unhandled_signals && unhandled_signal(tsk, signo)
 	    && printk_ratelimit()) {
 		pr_info("%s[%d]: unhandled signal %d code 0x%x at 0x" REG_FMT,
 			tsk->comm, task_pid_nr(tsk), signo, code, addr);
 		print_vma_addr(KERN_CONT " in ", instruction_pointer(regs));
 		pr_cont("\n");
 		__show_regs(regs);
 		dump_instr(KERN_INFO, regs);
 	}

 	force_sig_fault(signo, code, (void __user *)addr);
 }

 static void do_trap_error(struct pt_regs *regs, int signo, int code,
 	unsigned long addr, const char *str)
 {
 	current->thread.bad_cause = regs->cause;

 	if (user_mode(regs)) {
 		do_trap(regs, signo, code, addr);
 	} else {
 		if (!fixup_exception(regs))
 			die(regs, str);
 	}
 }

 #if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_RISCV_ALTERNATIVE)
 #define __trap_section __noinstr_section(".xip.traps")
 #else
 #define __trap_section noinstr
 #endif
 #define DO_ERROR_INFO(name, signo, code, str)					\
 asmlinkage __visible __trap_section void name(struct pt_regs *regs)		\
 {										\
 	if (user_mode(regs)) {							\
 		irqentry_enter_from_user_mode(regs);				\
 		do_trap_error(regs, signo, code, regs->epc, "Oops - " str);	\
 		irqentry_exit_to_user_mode(regs);				\
 	} else {								\
 		irqentry_state_t state = irqentry_nmi_enter(regs);		\
 		do_trap_error(regs, signo, code, regs->epc, "Oops - " str);	\
 		irqentry_nmi_exit(regs, state);					\
 	}									\
 }

 DO_ERROR_INFO(do_trap_unknown,
 	SIGILL, ILL_ILLTRP, "unknown exception");
 DO_ERROR_INFO(do_trap_insn_misaligned,
 	SIGBUS, BUS_ADRALN, "instruction address misaligned");
 DO_ERROR_INFO(do_trap_insn_fault,
 	SIGSEGV, SEGV_ACCERR, "instruction access fault");

 asmlinkage __visible __trap_section void do_trap_insn_illegal(struct pt_regs *regs)
 {
 	bool handled;

 	if (user_mode(regs)) {
 		irqentry_enter_from_user_mode(regs);

 		local_irq_enable();

 		handled = riscv_v_first_use_handler(regs);

 		local_irq_disable();

 		if (!handled)
 			do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
 				      "Oops - illegal instruction");

 		irqentry_exit_to_user_mode(regs);
 	} else {
 		irqentry_state_t state = irqentry_nmi_enter(regs);

 		do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
 			      "Oops - illegal instruction");

 		irqentry_nmi_exit(regs, state);
 	}
 }

 DO_ERROR_INFO(do_trap_load_fault,
 	SIGSEGV, SEGV_ACCERR, "load access fault");

 asmlinkage __visible __trap_section void do_trap_load_misaligned(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		irqentry_enter_from_user_mode(regs);

 		if (handle_misaligned_load(regs))
 			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
 			      "Oops - load address misaligned");

 		irqentry_exit_to_user_mode(regs);
 	} else {
 		irqentry_state_t state = irqentry_nmi_enter(regs);

 		if (handle_misaligned_load(regs))
 			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
 			      "Oops - load address misaligned");

 		irqentry_nmi_exit(regs, state);
 	}
 }

 asmlinkage __visible __trap_section void do_trap_store_misaligned(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		irqentry_enter_from_user_mode(regs);

 		if (handle_misaligned_store(regs))
 			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
 				"Oops - store (or AMO) address misaligned");

 		irqentry_exit_to_user_mode(regs);
 	} else {
 		irqentry_state_t state = irqentry_nmi_enter(regs);

 		if (handle_misaligned_store(regs))
 			do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
 				"Oops - store (or AMO) address misaligned");

 		irqentry_nmi_exit(regs, state);
 	}
 }
 DO_ERROR_INFO(do_trap_store_fault,
 	SIGSEGV, SEGV_ACCERR, "store (or AMO) access fault");
 DO_ERROR_INFO(do_trap_ecall_s,
 	SIGILL, ILL_ILLTRP, "environment call from S-mode");
 DO_ERROR_INFO(do_trap_ecall_m,
 	SIGILL, ILL_ILLTRP, "environment call from M-mode");

 static inline unsigned long get_break_insn_length(unsigned long pc)
 {
 	bug_insn_t insn;

 	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
 		return 0;

 	return GET_INSN_LENGTH(insn);
 }

 static bool probe_single_step_handler(struct pt_regs *regs)
 {
 	bool user = user_mode(regs);

 	return user ? uprobe_single_step_handler(regs) : kprobe_single_step_handler(regs);
 }

 static bool probe_breakpoint_handler(struct pt_regs *regs)
 {
 	bool user = user_mode(regs);

 	return user ? uprobe_breakpoint_handler(regs) : kprobe_breakpoint_handler(regs);
 }

 void handle_break(struct pt_regs *regs)
 {
 	if (probe_single_step_handler(regs))
 		return;

 	if (probe_breakpoint_handler(regs))
 		return;

 	current->thread.bad_cause = regs->cause;

 	if (user_mode(regs))
 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->epc);
 #ifdef CONFIG_KGDB
 	else if (notify_die(DIE_TRAP, "EBREAK", regs, 0, regs->cause, SIGTRAP)
 								== NOTIFY_STOP)
 		return;
 #endif
 	else if (report_bug(regs->epc, regs) == BUG_TRAP_TYPE_WARN ||
 		 handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN)
 		regs->epc += get_break_insn_length(regs->epc);
 	else
 		die(regs, "Kernel BUG");
 }

 asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		irqentry_enter_from_user_mode(regs);

 		handle_break(regs);

 		irqentry_exit_to_user_mode(regs);
 	} else {
 		irqentry_state_t state = irqentry_nmi_enter(regs);

 		handle_break(regs);

 		irqentry_nmi_exit(regs, state);
 	}
 }

 asmlinkage __visible __trap_section  __no_stack_protector
 void do_trap_ecall_u(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		long syscall = regs->a7;

 		regs->epc += 4;
 		regs->orig_a0 = regs->a0;
 		regs->a0 = -ENOSYS;

 		riscv_v_vstate_discard(regs);

 		syscall = syscall_enter_from_user_mode(regs, syscall);

 		add_random_kstack_offset();

 		if (syscall >= 0 && syscall < NR_syscalls)
 			syscall_handler(regs, syscall);

 		/*
 		 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
 		 * so the maximum stack offset is 1k bytes (10 bits).
 		 *
 		 * The actual entropy will be further reduced by the compiler when
 		 * applying stack alignment constraints: 16-byte (i.e. 4-bit) aligned
 		 * for RV32I or RV64I.
 		 *
 		 * The resulting 6 bits of entropy is seen in SP[9:4].
 		 */
 		choose_random_kstack_offset(get_random_u16());

 		syscall_exit_to_user_mode(regs);
 	} else {
 		irqentry_state_t state = irqentry_nmi_enter(regs);

 		do_trap_error(regs, SIGILL, ILL_ILLTRP, regs->epc,
 			"Oops - environment call from U-mode");

 		irqentry_nmi_exit(regs, state);
 	}

 }

 #ifdef CONFIG_MMU
 asmlinkage __visible noinstr void do_page_fault(struct pt_regs *regs)
 {
 	irqentry_state_t state = irqentry_enter(regs);

 	handle_page_fault(regs);

 	local_irq_disable();

 	irqentry_exit(regs, state);
 }
 #endif

 static void noinstr handle_riscv_irq(struct pt_regs *regs)
 {
 	struct pt_regs *old_regs;

 	irq_enter_rcu();
 	old_regs = set_irq_regs(regs);
 	handle_arch_irq(regs);
 	set_irq_regs(old_regs);
 	irq_exit_rcu();
 }

 asmlinkage void noinstr do_irq(struct pt_regs *regs)
 {
 	irqentry_state_t state = irqentry_enter(regs);

 	if (IS_ENABLED(CONFIG_IRQ_STACKS) && on_thread_stack())
 		call_on_irq_stack(regs, handle_riscv_irq);
 	else
 		handle_riscv_irq(regs);

 	irqentry_exit(regs, state);
 }

 #ifdef CONFIG_GENERIC_BUG
 int is_valid_bugaddr(unsigned long pc)
 {
 	bug_insn_t insn;

 	if (pc < VMALLOC_START)
 		return 0;
 	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
 		return 0;
 	if ((insn & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
 		return (insn == __BUG_INSN_32);
 	else
 		return ((insn & __COMPRESSED_INSN_MASK) == __BUG_INSN_16);
 }
 #endif /* CONFIG_GENERIC_BUG */

 #ifdef CONFIG_VMAP_STACK
 DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],
 		overflow_stack)__aligned(16);

 asmlinkage void handle_bad_stack(struct pt_regs *regs)
 {
 	unsigned long tsk_stk = (unsigned long)current->stack;
 	unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);

 	console_verbose();

 	pr_emerg("Insufficient stack space to handle exception!\n");
 	pr_emerg("Task stack:     [0x%016lx..0x%016lx]\n",
 			tsk_stk, tsk_stk + THREAD_SIZE);
 	pr_emerg("Overflow stack: [0x%016lx..0x%016lx]\n",
 			ovf_stk, ovf_stk + OVERFLOW_STACK_SIZE);

 	__show_regs(regs);
 	panic("Kernel stack overflow");

 	for (;;)
 		wait_for_interrupt();
 }
 #endif
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Copyright (C) 2012 Regents of the University of California
	*/

	#include <linux/cpu.h>
	#include <linux/kernel.h>
	#include <linux/init.h>
	#include <linux/randomize_kstack.h>
	#include <linux/sched.h>
	#include <linux/sched/debug.h>
	#include <linux/sched/signal.h>
	#include <linux/signal.h>
	#include <linux/kdebug.h>
	#include <linux/uaccess.h>
	#include <linux/kprobes.h>
	#include <linux/uprobes.h>
	#include <asm/uprobes.h>
	#include <linux/mm.h>
	#include <linux/module.h>
	#include <linux/irq.h>
	#include <linux/kexec.h>
	#include <linux/entry-common.h>

	#include <asm/asm-prototypes.h>
	#include <asm/bug.h>
	#include <asm/cfi.h>
	#include <asm/csr.h>
	#include <asm/processor.h>
	#include <asm/ptrace.h>
	#include <asm/syscall.h>
	#include <asm/thread_info.h>
	#include <asm/vector.h>
	#include <asm/irq_stack.h>

	int show_unhandled_signals = 1;

	static DEFINE_SPINLOCK(die_lock);

	static int copy_code(struct pt_regs regs, u16 val, const u16 *insns)
	{
	const void __user uaddr = (__force const void __user )insns;

	if (!user_mode(regs))
	return get_kernel_nofault(*val, insns);

	/* The user space code from other tasks cannot be accessed. */
	if (regs != task_pt_regs(current))
	return -EPERM;

	return copy_from_user_nofault(val, uaddr, sizeof(*val));
	}

	static void dump_instr(const char loglvl, struct pt_regs regs)
	{
	char str[sizeof("0000 ") * 12 + 2 + 1], *p = str;
	const u16 insns = (u16 )instruction_pointer(regs);
	long bad;
	u16 val;
	int i;

	for (i = -10; i < 2; i++) {
	bad = copy_code(regs, &val, &insns[i]);
	if (!bad) {
	p += sprintf(p, i == 0 ? "(%04hx) " : "%04hx ", val);
	} else {
	printk("%sCode: Unable to access instruction at 0x%px.\n",
	loglvl, &insns[i]);
	return;
	}
	}
	printk("%sCode: %s\n", loglvl, str);
	}

	void die(struct pt_regs regs, const char str)
	{
	static int die_counter;
	int ret;
	long cause;
	unsigned long flags;

	oops_enter();

	spin_lock_irqsave(&die_lock, flags);
	console_verbose();
	bust_spinlocks(1);

	pr_emerg("%s [#%d]\n", str, ++die_counter);
	print_modules();
	if (regs) {
	show_regs(regs);
	dump_instr(KERN_EMERG, regs);
	}

	cause = regs ? regs->cause : -1;
	ret = notify_die(DIE_OOPS, str, regs, 0, cause, SIGSEGV);

	if (kexec_should_crash(current))
	crash_kexec(regs);

	bust_spinlocks(0);
	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
	spin_unlock_irqrestore(&die_lock, flags);
	oops_exit();

	if (in_interrupt())
	panic("Fatal exception in interrupt");
	if (panic_on_oops)
	panic("Fatal exception");
	if (ret != NOTIFY_STOP)
	make_task_dead(SIGSEGV);
	}

	void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr)
	{
	struct task_struct *tsk = current;

	if (show_unhandled_signals && unhandled_signal(tsk, signo)
	&& printk_ratelimit()) {
	pr_info("%s[%d]: unhandled signal %d code 0x%x at 0x" REG_FMT,
	tsk->comm, task_pid_nr(tsk), signo, code, addr);
	print_vma_addr(KERN_CONT " in ", instruction_pointer(regs));
	pr_cont("\n");
	__show_regs(regs);
	dump_instr(KERN_INFO, regs);
	}

	force_sig_fault(signo, code, (void __user *)addr);
	}

	static void do_trap_error(struct pt_regs *regs, int signo, int code,
	unsigned long addr, const char *str)
	{
	current->thread.bad_cause = regs->cause;

	if (user_mode(regs)) {
	do_trap(regs, signo, code, addr);
	} else {
	if (!fixup_exception(regs))
	die(regs, str);
	}
	}

	#if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_RISCV_ALTERNATIVE)
	#define __trap_section __noinstr_section(".xip.traps")
	#else
	#define __trap_section noinstr
	#endif
	#define DO_ERROR_INFO(name, signo, code, str) \
	asmlinkage __visible __trap_section void name(struct pt_regs *regs) \
	{ \
	if (user_mode(regs)) { \
	irqentry_enter_from_user_mode(regs); \
	do_trap_error(regs, signo, code, regs->epc, "Oops - " str); \
	irqentry_exit_to_user_mode(regs); \
	} else { \
	irqentry_state_t state = irqentry_nmi_enter(regs); \
	do_trap_error(regs, signo, code, regs->epc, "Oops - " str); \
	irqentry_nmi_exit(regs, state); \
	} \
	}

	DO_ERROR_INFO(do_trap_unknown,
	SIGILL, ILL_ILLTRP, "unknown exception");
	DO_ERROR_INFO(do_trap_insn_misaligned,
	SIGBUS, BUS_ADRALN, "instruction address misaligned");
	DO_ERROR_INFO(do_trap_insn_fault,
	SIGSEGV, SEGV_ACCERR, "instruction access fault");

	asmlinkage __visible __trap_section void do_trap_insn_illegal(struct pt_regs *regs)
	{
	bool handled;

	if (user_mode(regs)) {
	irqentry_enter_from_user_mode(regs);

	local_irq_enable();

	handled = riscv_v_first_use_handler(regs);

	local_irq_disable();

	if (!handled)
	do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
	"Oops - illegal instruction");

	irqentry_exit_to_user_mode(regs);
	} else {
	irqentry_state_t state = irqentry_nmi_enter(regs);

	do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
	"Oops - illegal instruction");

	irqentry_nmi_exit(regs, state);
	}
	}

	DO_ERROR_INFO(do_trap_load_fault,
	SIGSEGV, SEGV_ACCERR, "load access fault");

	asmlinkage __visible __trap_section void do_trap_load_misaligned(struct pt_regs *regs)
	{
	if (user_mode(regs)) {
	irqentry_enter_from_user_mode(regs);

	if (handle_misaligned_load(regs))
	do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
	"Oops - load address misaligned");

	irqentry_exit_to_user_mode(regs);
	} else {
	irqentry_state_t state = irqentry_nmi_enter(regs);

	if (handle_misaligned_load(regs))
	do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
	"Oops - load address misaligned");

	irqentry_nmi_exit(regs, state);
	}
	}

	asmlinkage __visible __trap_section void do_trap_store_misaligned(struct pt_regs *regs)
	{
	if (user_mode(regs)) {
	irqentry_enter_from_user_mode(regs);

	if (handle_misaligned_store(regs))
	do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
	"Oops - store (or AMO) address misaligned");

	irqentry_exit_to_user_mode(regs);
	} else {
	irqentry_state_t state = irqentry_nmi_enter(regs);

	if (handle_misaligned_store(regs))
	do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
	"Oops - store (or AMO) address misaligned");

	irqentry_nmi_exit(regs, state);
	}
	}
	DO_ERROR_INFO(do_trap_store_fault,
	SIGSEGV, SEGV_ACCERR, "store (or AMO) access fault");
	DO_ERROR_INFO(do_trap_ecall_s,
	SIGILL, ILL_ILLTRP, "environment call from S-mode");
	DO_ERROR_INFO(do_trap_ecall_m,
	SIGILL, ILL_ILLTRP, "environment call from M-mode");

	static inline unsigned long get_break_insn_length(unsigned long pc)
	{
	bug_insn_t insn;

	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
	return 0;

	return GET_INSN_LENGTH(insn);
	}

	static bool probe_single_step_handler(struct pt_regs *regs)
	{
	bool user = user_mode(regs);

	return user ? uprobe_single_step_handler(regs) : kprobe_single_step_handler(regs);
	}

	static bool probe_breakpoint_handler(struct pt_regs *regs)
	{
	bool user = user_mode(regs);

	return user ? uprobe_breakpoint_handler(regs) : kprobe_breakpoint_handler(regs);
	}

	void handle_break(struct pt_regs *regs)
	{
	if (probe_single_step_handler(regs))
	return;

	if (probe_breakpoint_handler(regs))
	return;

	current->thread.bad_cause = regs->cause;

	if (user_mode(regs))
	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->epc);
	#ifdef CONFIG_KGDB
	else if (notify_die(DIE_TRAP, "EBREAK", regs, 0, regs->cause, SIGTRAP)
	== NOTIFY_STOP)
	return;
	#endif
	else if (report_bug(regs->epc, regs) == BUG_TRAP_TYPE_WARN \|\|
	handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN)
	regs->epc += get_break_insn_length(regs->epc);
	else
	die(regs, "Kernel BUG");
	}

	asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
	{
	if (user_mode(regs)) {
	irqentry_enter_from_user_mode(regs);

	handle_break(regs);

	irqentry_exit_to_user_mode(regs);
	} else {
	irqentry_state_t state = irqentry_nmi_enter(regs);

	handle_break(regs);

	irqentry_nmi_exit(regs, state);
	}
	}

	asmlinkage __visible __trap_section __no_stack_protector
	void do_trap_ecall_u(struct pt_regs *regs)
	{
	if (user_mode(regs)) {
	long syscall = regs->a7;

	regs->epc += 4;
	regs->orig_a0 = regs->a0;
	regs->a0 = -ENOSYS;

	riscv_v_vstate_discard(regs);

	syscall = syscall_enter_from_user_mode(regs, syscall);

	add_random_kstack_offset();

	if (syscall >= 0 && syscall < NR_syscalls)
	syscall_handler(regs, syscall);

	/*
	* Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
	* so the maximum stack offset is 1k bytes (10 bits).
	*
	* The actual entropy will be further reduced by the compiler when
	* applying stack alignment constraints: 16-byte (i.e. 4-bit) aligned
	* for RV32I or RV64I.
	*
	* The resulting 6 bits of entropy is seen in SP[9:4].
	*/
	choose_random_kstack_offset(get_random_u16());

	syscall_exit_to_user_mode(regs);
	} else {
	irqentry_state_t state = irqentry_nmi_enter(regs);

	do_trap_error(regs, SIGILL, ILL_ILLTRP, regs->epc,
	"Oops - environment call from U-mode");

	irqentry_nmi_exit(regs, state);
	}

	}

	#ifdef CONFIG_MMU
	asmlinkage __visible noinstr void do_page_fault(struct pt_regs *regs)
	{
	irqentry_state_t state = irqentry_enter(regs);

	handle_page_fault(regs);

	local_irq_disable();

	irqentry_exit(regs, state);
	}
	#endif

	static void noinstr handle_riscv_irq(struct pt_regs *regs)
	{
	struct pt_regs *old_regs;

	irq_enter_rcu();
	old_regs = set_irq_regs(regs);
	handle_arch_irq(regs);
	set_irq_regs(old_regs);
	irq_exit_rcu();
	}

	asmlinkage void noinstr do_irq(struct pt_regs *regs)
	{
	irqentry_state_t state = irqentry_enter(regs);

	if (IS_ENABLED(CONFIG_IRQ_STACKS) && on_thread_stack())
	call_on_irq_stack(regs, handle_riscv_irq);
	else
	handle_riscv_irq(regs);

	irqentry_exit(regs, state);
	}

	#ifdef CONFIG_GENERIC_BUG
	int is_valid_bugaddr(unsigned long pc)
	{
	bug_insn_t insn;

	if (pc < VMALLOC_START)
	return 0;
	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
	return 0;
	if ((insn & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
	return (insn == __BUG_INSN_32);
	else
	return ((insn & __COMPRESSED_INSN_MASK) == __BUG_INSN_16);
	}
	#endif /* CONFIG_GENERIC_BUG */

	#ifdef CONFIG_VMAP_STACK
	DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],
	overflow_stack)__aligned(16);

	asmlinkage void handle_bad_stack(struct pt_regs *regs)
	{
	unsigned long tsk_stk = (unsigned long)current->stack;
	unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);

	console_verbose();

	pr_emerg("Insufficient stack space to handle exception!\n");
	pr_emerg("Task stack: [0x%016lx..0x%016lx]\n",
	tsk_stk, tsk_stk + THREAD_SIZE);
	pr_emerg("Overflow stack: [0x%016lx..0x%016lx]\n",
	ovf_stk, ovf_stk + OVERFLOW_STACK_SIZE);

	__show_regs(regs);
	panic("Kernel stack overflow");

	for (;;)
	wait_for_interrupt();
	}
	#endif