Initial import

1 files changed, 731 insertions, 0 deletions

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
new file mode 100644
index 000000000..bddd04d03
--- /dev/null
+++ b/arch/arm64/kernel/entry.S
@@ -0,0 +1,731 @@
+/*
+ * Low-level exception handling code
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Authors:	Catalin Marinas <catalin.marinas@arm.com>
+ *		Will Deacon <will.deacon@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <linux/init.h>
+#include <linux/linkage.h>
+
+#include <asm/alternative-asm.h>
+#include <asm/assembler.h>
+#include <asm/asm-offsets.h>
+#include <asm/cpufeature.h>
+#include <asm/errno.h>
+#include <asm/esr.h>
+#include <asm/thread_info.h>
+#include <asm/unistd.h>
+
+/*
+ * Context tracking subsystem.  Used to instrument transitions
+ * between user and kernel mode.
+ */
+	.macro ct_user_exit, syscall = 0
+#ifdef CONFIG_CONTEXT_TRACKING
+	bl	context_tracking_user_exit
+	.if \syscall == 1
+	/*
+	 * Save/restore needed during syscalls.  Restore syscall arguments from
+	 * the values already saved on stack during kernel_entry.
+	 */
+	ldp	x0, x1, [sp]
+	ldp	x2, x3, [sp, #S_X2]
+	ldp	x4, x5, [sp, #S_X4]
+	ldp	x6, x7, [sp, #S_X6]
+	.endif
+#endif
+	.endm
+
+	.macro ct_user_enter
+#ifdef CONFIG_CONTEXT_TRACKING
+	bl	context_tracking_user_enter
+#endif
+	.endm
+
+/*
+ * Bad Abort numbers
+ *-----------------
+ */
+#define BAD_SYNC	0
+#define BAD_IRQ		1
+#define BAD_FIQ		2
+#define BAD_ERROR	3
+
+	.macro	kernel_entry, el, regsize = 64
+	sub	sp, sp, #S_FRAME_SIZE
+	.if	\regsize == 32
+	mov	w0, w0				// zero upper 32 bits of x0
+	.endif
+	stp	x0, x1, [sp, #16 * 0]
+	stp	x2, x3, [sp, #16 * 1]
+	stp	x4, x5, [sp, #16 * 2]
+	stp	x6, x7, [sp, #16 * 3]
+	stp	x8, x9, [sp, #16 * 4]
+	stp	x10, x11, [sp, #16 * 5]
+	stp	x12, x13, [sp, #16 * 6]
+	stp	x14, x15, [sp, #16 * 7]
+	stp	x16, x17, [sp, #16 * 8]
+	stp	x18, x19, [sp, #16 * 9]
+	stp	x20, x21, [sp, #16 * 10]
+	stp	x22, x23, [sp, #16 * 11]
+	stp	x24, x25, [sp, #16 * 12]
+	stp	x26, x27, [sp, #16 * 13]
+	stp	x28, x29, [sp, #16 * 14]
+
+	.if	\el == 0
+	mrs	x21, sp_el0
+	get_thread_info tsk			// Ensure MDSCR_EL1.SS is clear,
+	ldr	x19, [tsk, #TI_FLAGS]		// since we can unmask debug
+	disable_step_tsk x19, x20		// exceptions when scheduling.
+	.else
+	add	x21, sp, #S_FRAME_SIZE
+	.endif
+	mrs	x22, elr_el1
+	mrs	x23, spsr_el1
+	stp	lr, x21, [sp, #S_LR]
+	stp	x22, x23, [sp, #S_PC]
+
+	/*
+	 * Set syscallno to -1 by default (overridden later if real syscall).
+	 */
+	.if	\el == 0
+	mvn	x21, xzr
+	str	x21, [sp, #S_SYSCALLNO]
+	.endif
+
+	/*
+	 * Registers that may be useful after this macro is invoked:
+	 *
+	 * x21 - aborted SP
+	 * x22 - aborted PC
+	 * x23 - aborted PSTATE
+	*/
+	.endm
+
+	.macro	kernel_exit, el, ret = 0
+	ldp	x21, x22, [sp, #S_PC]		// load ELR, SPSR
+	.if	\el == 0
+	ct_user_enter
+	ldr	x23, [sp, #S_SP]		// load return stack pointer
+	msr	sp_el0, x23
+
+#ifdef CONFIG_ARM64_ERRATUM_845719
+	alternative_insn						\
+	"nop",								\
+	"tbz x22, #4, 1f",						\
+	ARM64_WORKAROUND_845719
+#ifdef CONFIG_PID_IN_CONTEXTIDR
+	alternative_insn						\
+	"nop; nop",							\
+	"mrs x29, contextidr_el1; msr contextidr_el1, x29; 1:",		\
+	ARM64_WORKAROUND_845719
+#else
+	alternative_insn						\
+	"nop",								\
+	"msr contextidr_el1, xzr; 1:",					\
+	ARM64_WORKAROUND_845719
+#endif
+#endif
+	.endif
+	msr	elr_el1, x21			// set up the return data
+	msr	spsr_el1, x22
+	.if	\ret
+	ldr	x1, [sp, #S_X1]			// preserve x0 (syscall return)
+	.else
+	ldp	x0, x1, [sp, #16 * 0]
+	.endif
+	ldp	x2, x3, [sp, #16 * 1]
+	ldp	x4, x5, [sp, #16 * 2]
+	ldp	x6, x7, [sp, #16 * 3]
+	ldp	x8, x9, [sp, #16 * 4]
+	ldp	x10, x11, [sp, #16 * 5]
+	ldp	x12, x13, [sp, #16 * 6]
+	ldp	x14, x15, [sp, #16 * 7]
+	ldp	x16, x17, [sp, #16 * 8]
+	ldp	x18, x19, [sp, #16 * 9]
+	ldp	x20, x21, [sp, #16 * 10]
+	ldp	x22, x23, [sp, #16 * 11]
+	ldp	x24, x25, [sp, #16 * 12]
+	ldp	x26, x27, [sp, #16 * 13]
+	ldp	x28, x29, [sp, #16 * 14]
+	ldr	lr, [sp, #S_LR]
+	add	sp, sp, #S_FRAME_SIZE		// restore sp
+	eret					// return to kernel
+	.endm
+
+	.macro	get_thread_info, rd
+	mov	\rd, sp
+	and	\rd, \rd, #~(THREAD_SIZE - 1)	// top of stack
+	.endm
+
+/*
+ * These are the registers used in the syscall handler, and allow us to
+ * have in theory up to 7 arguments to a function - x0 to x6.
+ *
+ * x7 is reserved for the system call number in 32-bit mode.
+ */
+sc_nr	.req	x25		// number of system calls
+scno	.req	x26		// syscall number
+stbl	.req	x27		// syscall table pointer
+tsk	.req	x28		// current thread_info
+
+/*
+ * Interrupt handling.
+ */
+	.macro	irq_handler
+	adrp	x1, handle_arch_irq
+	ldr	x1, [x1, #:lo12:handle_arch_irq]
+	mov	x0, sp
+	blr	x1
+	.endm
+
+	.text
+
+/*
+ * Exception vectors.
+ */
+
+	.align	11
+ENTRY(vectors)
+	ventry	el1_sync_invalid		// Synchronous EL1t
+	ventry	el1_irq_invalid			// IRQ EL1t
+	ventry	el1_fiq_invalid			// FIQ EL1t
+	ventry	el1_error_invalid		// Error EL1t
+
+	ventry	el1_sync			// Synchronous EL1h
+	ventry	el1_irq				// IRQ EL1h
+	ventry	el1_fiq_invalid			// FIQ EL1h
+	ventry	el1_error_invalid		// Error EL1h
+
+	ventry	el0_sync			// Synchronous 64-bit EL0
+	ventry	el0_irq				// IRQ 64-bit EL0
+	ventry	el0_fiq_invalid			// FIQ 64-bit EL0
+	ventry	el0_error_invalid		// Error 64-bit EL0
+
+#ifdef CONFIG_COMPAT
+	ventry	el0_sync_compat			// Synchronous 32-bit EL0
+	ventry	el0_irq_compat			// IRQ 32-bit EL0
+	ventry	el0_fiq_invalid_compat		// FIQ 32-bit EL0
+	ventry	el0_error_invalid_compat	// Error 32-bit EL0
+#else
+	ventry	el0_sync_invalid		// Synchronous 32-bit EL0
+	ventry	el0_irq_invalid			// IRQ 32-bit EL0
+	ventry	el0_fiq_invalid			// FIQ 32-bit EL0
+	ventry	el0_error_invalid		// Error 32-bit EL0
+#endif
+END(vectors)
+
+/*
+ * Invalid mode handlers
+ */
+	.macro	inv_entry, el, reason, regsize = 64
+	kernel_entry el, \regsize
+	mov	x0, sp
+	mov	x1, #\reason
+	mrs	x2, esr_el1
+	b	bad_mode
+	.endm
+
+el0_sync_invalid:
+	inv_entry 0, BAD_SYNC
+ENDPROC(el0_sync_invalid)
+
+el0_irq_invalid:
+	inv_entry 0, BAD_IRQ
+ENDPROC(el0_irq_invalid)
+
+el0_fiq_invalid:
+	inv_entry 0, BAD_FIQ
+ENDPROC(el0_fiq_invalid)
+
+el0_error_invalid:
+	inv_entry 0, BAD_ERROR
+ENDPROC(el0_error_invalid)
+
+#ifdef CONFIG_COMPAT
+el0_fiq_invalid_compat:
+	inv_entry 0, BAD_FIQ, 32
+ENDPROC(el0_fiq_invalid_compat)
+
+el0_error_invalid_compat:
+	inv_entry 0, BAD_ERROR, 32
+ENDPROC(el0_error_invalid_compat)
+#endif
+
+el1_sync_invalid:
+	inv_entry 1, BAD_SYNC
+ENDPROC(el1_sync_invalid)
+
+el1_irq_invalid:
+	inv_entry 1, BAD_IRQ
+ENDPROC(el1_irq_invalid)
+
+el1_fiq_invalid:
+	inv_entry 1, BAD_FIQ
+ENDPROC(el1_fiq_invalid)
+
+el1_error_invalid:
+	inv_entry 1, BAD_ERROR
+ENDPROC(el1_error_invalid)
+
+/*
+ * EL1 mode handlers.
+ */
+	.align	6
+el1_sync:
+	kernel_entry 1
+	mrs	x1, esr_el1			// read the syndrome register
+	lsr	x24, x1, #ESR_ELx_EC_SHIFT	// exception class
+	cmp	x24, #ESR_ELx_EC_DABT_CUR	// data abort in EL1
+	b.eq	el1_da
+	cmp	x24, #ESR_ELx_EC_SYS64		// configurable trap
+	b.eq	el1_undef
+	cmp	x24, #ESR_ELx_EC_SP_ALIGN	// stack alignment exception
+	b.eq	el1_sp_pc
+	cmp	x24, #ESR_ELx_EC_PC_ALIGN	// pc alignment exception
+	b.eq	el1_sp_pc
+	cmp	x24, #ESR_ELx_EC_UNKNOWN	// unknown exception in EL1
+	b.eq	el1_undef
+	cmp	x24, #ESR_ELx_EC_BREAKPT_CUR	// debug exception in EL1
+	b.ge	el1_dbg
+	b	el1_inv
+el1_da:
+	/*
+	 * Data abort handling
+	 */
+	mrs	x0, far_el1
+	enable_dbg
+	// re-enable interrupts if they were enabled in the aborted context
+	tbnz	x23, #7, 1f			// PSR_I_BIT
+	enable_irq
+1:
+	mov	x2, sp				// struct pt_regs
+	bl	do_mem_abort
+
+	// disable interrupts before pulling preserved data off the stack
+	disable_irq
+	kernel_exit 1
+el1_sp_pc:
+	/*
+	 * Stack or PC alignment exception handling
+	 */
+	mrs	x0, far_el1
+	enable_dbg
+	mov	x2, sp
+	b	do_sp_pc_abort
+el1_undef:
+	/*
+	 * Undefined instruction
+	 */
+	enable_dbg
+	mov	x0, sp
+	b	do_undefinstr
+el1_dbg:
+	/*
+	 * Debug exception handling
+	 */
+	cmp	x24, #ESR_ELx_EC_BRK64		// if BRK64
+	cinc	x24, x24, eq			// set bit '0'
+	tbz	x24, #0, el1_inv		// EL1 only
+	mrs	x0, far_el1
+	mov	x2, sp				// struct pt_regs
+	bl	do_debug_exception
+	kernel_exit 1
+el1_inv:
+	// TODO: add support for undefined instructions in kernel mode
+	enable_dbg
+	mov	x0, sp
+	mov	x1, #BAD_SYNC
+	mrs	x2, esr_el1
+	b	bad_mode
+ENDPROC(el1_sync)
+
+	.align	6
+el1_irq:
+	kernel_entry 1
+	enable_dbg
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bl	trace_hardirqs_off
+#endif
+
+	irq_handler
+
+#ifdef CONFIG_PREEMPT
+	get_thread_info tsk
+	ldr	w24, [tsk, #TI_PREEMPT]		// get preempt count
+	cbnz	w24, 1f				// preempt count != 0
+	ldr	x0, [tsk, #TI_FLAGS]		// get flags
+	tbz	x0, #TIF_NEED_RESCHED, 1f	// needs rescheduling?
+	bl	el1_preempt
+1:
+#endif
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bl	trace_hardirqs_on
+#endif
+	kernel_exit 1
+ENDPROC(el1_irq)
+
+#ifdef CONFIG_PREEMPT
+el1_preempt:
+	mov	x24, lr
+1:	bl	preempt_schedule_irq		// irq en/disable is done inside
+	ldr	x0, [tsk, #TI_FLAGS]		// get new tasks TI_FLAGS
+	tbnz	x0, #TIF_NEED_RESCHED, 1b	// needs rescheduling?
+	ret	x24
+#endif
+
+/*
+ * EL0 mode handlers.
+ */
+	.align	6
+el0_sync:
+	kernel_entry 0
+	mrs	x25, esr_el1			// read the syndrome register
+	lsr	x24, x25, #ESR_ELx_EC_SHIFT	// exception class
+	cmp	x24, #ESR_ELx_EC_SVC64		// SVC in 64-bit state
+	b.eq	el0_svc
+	cmp	x24, #ESR_ELx_EC_DABT_LOW	// data abort in EL0
+	b.eq	el0_da
+	cmp	x24, #ESR_ELx_EC_IABT_LOW	// instruction abort in EL0
+	b.eq	el0_ia
+	cmp	x24, #ESR_ELx_EC_FP_ASIMD	// FP/ASIMD access
+	b.eq	el0_fpsimd_acc
+	cmp	x24, #ESR_ELx_EC_FP_EXC64	// FP/ASIMD exception
+	b.eq	el0_fpsimd_exc
+	cmp	x24, #ESR_ELx_EC_SYS64		// configurable trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_SP_ALIGN	// stack alignment exception
+	b.eq	el0_sp_pc
+	cmp	x24, #ESR_ELx_EC_PC_ALIGN	// pc alignment exception
+	b.eq	el0_sp_pc
+	cmp	x24, #ESR_ELx_EC_UNKNOWN	// unknown exception in EL0
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_BREAKPT_LOW	// debug exception in EL0
+	b.ge	el0_dbg
+	b	el0_inv
+
+#ifdef CONFIG_COMPAT
+	.align	6
+el0_sync_compat:
+	kernel_entry 0, 32
+	mrs	x25, esr_el1			// read the syndrome register
+	lsr	x24, x25, #ESR_ELx_EC_SHIFT	// exception class
+	cmp	x24, #ESR_ELx_EC_SVC32		// SVC in 32-bit state
+	b.eq	el0_svc_compat
+	cmp	x24, #ESR_ELx_EC_DABT_LOW	// data abort in EL0
+	b.eq	el0_da
+	cmp	x24, #ESR_ELx_EC_IABT_LOW	// instruction abort in EL0
+	b.eq	el0_ia
+	cmp	x24, #ESR_ELx_EC_FP_ASIMD	// FP/ASIMD access
+	b.eq	el0_fpsimd_acc
+	cmp	x24, #ESR_ELx_EC_FP_EXC32	// FP/ASIMD exception
+	b.eq	el0_fpsimd_exc
+	cmp	x24, #ESR_ELx_EC_UNKNOWN	// unknown exception in EL0
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_CP15_32	// CP15 MRC/MCR trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_CP15_64	// CP15 MRRC/MCRR trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_CP14_MR	// CP14 MRC/MCR trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_CP14_LS	// CP14 LDC/STC trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_CP14_64	// CP14 MRRC/MCRR trap
+	b.eq	el0_undef
+	cmp	x24, #ESR_ELx_EC_BREAKPT_LOW	// debug exception in EL0
+	b.ge	el0_dbg
+	b	el0_inv
+el0_svc_compat:
+	/*
+	 * AArch32 syscall handling
+	 */
+	adrp	stbl, compat_sys_call_table	// load compat syscall table pointer
+	uxtw	scno, w7			// syscall number in w7 (r7)
+	mov     sc_nr, #__NR_compat_syscalls
+	b	el0_svc_naked
+
+	.align	6
+el0_irq_compat:
+	kernel_entry 0, 32
+	b	el0_irq_naked
+#endif
+
+el0_da:
+	/*
+	 * Data abort handling
+	 */
+	mrs	x26, far_el1
+	// enable interrupts before calling the main handler
+	enable_dbg_and_irq
+	ct_user_exit
+	bic	x0, x26, #(0xff << 56)
+	mov	x1, x25
+	mov	x2, sp
+	bl	do_mem_abort
+	b	ret_to_user
+el0_ia:
+	/*
+	 * Instruction abort handling
+	 */
+	mrs	x26, far_el1
+	// enable interrupts before calling the main handler
+	enable_dbg_and_irq
+	ct_user_exit
+	mov	x0, x26
+	orr	x1, x25, #1 << 24		// use reserved ISS bit for instruction aborts
+	mov	x2, sp
+	bl	do_mem_abort
+	b	ret_to_user
+el0_fpsimd_acc:
+	/*
+	 * Floating Point or Advanced SIMD access
+	 */
+	enable_dbg
+	ct_user_exit
+	mov	x0, x25
+	mov	x1, sp
+	bl	do_fpsimd_acc
+	b	ret_to_user
+el0_fpsimd_exc:
+	/*
+	 * Floating Point or Advanced SIMD exception
+	 */
+	enable_dbg
+	ct_user_exit
+	mov	x0, x25
+	mov	x1, sp
+	bl	do_fpsimd_exc
+	b	ret_to_user
+el0_sp_pc:
+	/*
+	 * Stack or PC alignment exception handling
+	 */
+	mrs	x26, far_el1
+	// enable interrupts before calling the main handler
+	enable_dbg_and_irq
+	ct_user_exit
+	mov	x0, x26
+	mov	x1, x25
+	mov	x2, sp
+	bl	do_sp_pc_abort
+	b	ret_to_user
+el0_undef:
+	/*
+	 * Undefined instruction
+	 */
+	// enable interrupts before calling the main handler
+	enable_dbg_and_irq
+	ct_user_exit
+	mov	x0, sp
+	bl	do_undefinstr
+	b	ret_to_user
+el0_dbg:
+	/*
+	 * Debug exception handling
+	 */
+	tbnz	x24, #0, el0_inv		// EL0 only
+	mrs	x0, far_el1
+	mov	x1, x25
+	mov	x2, sp
+	bl	do_debug_exception
+	enable_dbg
+	ct_user_exit
+	b	ret_to_user
+el0_inv:
+	enable_dbg
+	ct_user_exit
+	mov	x0, sp
+	mov	x1, #BAD_SYNC
+	mrs	x2, esr_el1
+	bl	bad_mode
+	b	ret_to_user
+ENDPROC(el0_sync)
+
+	.align	6
+el0_irq:
+	kernel_entry 0
+el0_irq_naked:
+	enable_dbg
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bl	trace_hardirqs_off
+#endif
+
+	ct_user_exit
+	irq_handler
+
+#ifdef CONFIG_TRACE_IRQFLAGS
+	bl	trace_hardirqs_on
+#endif
+	b	ret_to_user
+ENDPROC(el0_irq)
+
+/*
+ * Register switch for AArch64. The callee-saved registers need to be saved
+ * and restored. On entry:
+ *   x0 = previous task_struct (must be preserved across the switch)
+ *   x1 = next task_struct
+ * Previous and next are guaranteed not to be the same.
+ *
+ */
+ENTRY(cpu_switch_to)
+	add	x8, x0, #THREAD_CPU_CONTEXT
+	mov	x9, sp
+	stp	x19, x20, [x8], #16		// store callee-saved registers
+	stp	x21, x22, [x8], #16
+	stp	x23, x24, [x8], #16
+	stp	x25, x26, [x8], #16
+	stp	x27, x28, [x8], #16
+	stp	x29, x9, [x8], #16
+	str	lr, [x8]
+	add	x8, x1, #THREAD_CPU_CONTEXT
+	ldp	x19, x20, [x8], #16		// restore callee-saved registers
+	ldp	x21, x22, [x8], #16
+	ldp	x23, x24, [x8], #16
+	ldp	x25, x26, [x8], #16
+	ldp	x27, x28, [x8], #16
+	ldp	x29, x9, [x8], #16
+	ldr	lr, [x8]
+	mov	sp, x9
+	ret
+ENDPROC(cpu_switch_to)
+
+/*
+ * This is the fast syscall return path.  We do as little as possible here,
+ * and this includes saving x0 back into the kernel stack.
+ */
+ret_fast_syscall:
+	disable_irq				// disable interrupts
+	ldr	x1, [tsk, #TI_FLAGS]
+	and	x2, x1, #_TIF_WORK_MASK
+	cbnz	x2, fast_work_pending
+	enable_step_tsk x1, x2
+	kernel_exit 0, ret = 1
+
+/*
+ * Ok, we need to do extra processing, enter the slow path.
+ */
+fast_work_pending:
+	str	x0, [sp, #S_X0]			// returned x0
+work_pending:
+	tbnz	x1, #TIF_NEED_RESCHED, work_resched
+	/* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */
+	ldr	x2, [sp, #S_PSTATE]
+	mov	x0, sp				// 'regs'
+	tst	x2, #PSR_MODE_MASK		// user mode regs?
+	b.ne	no_work_pending			// returning to kernel
+	enable_irq				// enable interrupts for do_notify_resume()
+	bl	do_notify_resume
+	b	ret_to_user
+work_resched:
+	bl	schedule
+
+/*
+ * "slow" syscall return path.
+ */
+ret_to_user:
+	disable_irq				// disable interrupts
+	ldr	x1, [tsk, #TI_FLAGS]
+	and	x2, x1, #_TIF_WORK_MASK
+	cbnz	x2, work_pending
+	enable_step_tsk x1, x2
+no_work_pending:
+	kernel_exit 0, ret = 0
+ENDPROC(ret_to_user)
+
+/*
+ * This is how we return from a fork.
+ */
+ENTRY(ret_from_fork)
+	bl	schedule_tail
+	cbz	x19, 1f				// not a kernel thread
+	mov	x0, x20
+	blr	x19
+1:	get_thread_info tsk
+	b	ret_to_user
+ENDPROC(ret_from_fork)
+
+/*
+ * SVC handler.
+ */
+	.align	6
+el0_svc:
+	adrp	stbl, sys_call_table		// load syscall table pointer
+	uxtw	scno, w8			// syscall number in w8
+	mov	sc_nr, #__NR_syscalls
+el0_svc_naked:					// compat entry point
+	stp	x0, scno, [sp, #S_ORIG_X0]	// save the original x0 and syscall number
+	enable_dbg_and_irq
+	ct_user_exit 1
+
+	ldr	x16, [tsk, #TI_FLAGS]		// check for syscall hooks
+	tst	x16, #_TIF_SYSCALL_WORK
+	b.ne	__sys_trace
+	cmp     scno, sc_nr                     // check upper syscall limit
+	b.hs	ni_sys
+	ldr	x16, [stbl, scno, lsl #3]	// address in the syscall table
+	blr	x16				// call sys_* routine
+	b	ret_fast_syscall
+ni_sys:
+	mov	x0, sp
+	bl	do_ni_syscall
+	b	ret_fast_syscall
+ENDPROC(el0_svc)
+
+	/*
+	 * This is the really slow path.  We're going to be doing context
+	 * switches, and waiting for our parent to respond.
+	 */
+__sys_trace:
+	mov	w0, #-1				// set default errno for
+	cmp     scno, x0			// user-issued syscall(-1)
+	b.ne	1f
+	mov	x0, #-ENOSYS
+	str	x0, [sp, #S_X0]
+1:	mov	x0, sp
+	bl	syscall_trace_enter
+	cmp	w0, #-1				// skip the syscall?
+	b.eq	__sys_trace_return_skipped
+	uxtw	scno, w0			// syscall number (possibly new)
+	mov	x1, sp				// pointer to regs
+	cmp	scno, sc_nr			// check upper syscall limit
+	b.hs	__ni_sys_trace
+	ldp	x0, x1, [sp]			// restore the syscall args
+	ldp	x2, x3, [sp, #S_X2]
+	ldp	x4, x5, [sp, #S_X4]
+	ldp	x6, x7, [sp, #S_X6]
+	ldr	x16, [stbl, scno, lsl #3]	// address in the syscall table
+	blr	x16				// call sys_* routine
+
+__sys_trace_return:
+	str	x0, [sp, #S_X0]			// save returned x0
+__sys_trace_return_skipped:
+	mov	x0, sp
+	bl	syscall_trace_exit
+	b	ret_to_user
+
+__ni_sys_trace:
+	mov	x0, sp
+	bl	do_ni_syscall
+	b	__sys_trace_return
+
+/*
+ * Special system call wrappers.
+ */
+ENTRY(sys_rt_sigreturn_wrapper)
+	mov	x0, sp
+	b	sys_rt_sigreturn
+ENDPROC(sys_rt_sigreturn_wrapper)