arch/x86/kernel/ftrace_64.S - linux - Git at Google

 /* SPDX-License-Identifier: GPL-2.0 */
 /*
  *  Copyright (C) 2014  Steven Rostedt, Red Hat Inc
  */

 #include <linux/cfi_types.h>
 #include <linux/linkage.h>
 #include <asm/asm-offsets.h>
 #include <asm/ptrace.h>
 #include <asm/ftrace.h>
 #include <asm/export.h>
 #include <asm/nospec-branch.h>
 #include <asm/unwind_hints.h>
 #include <asm/frame.h>

 	.code64
 	.section .text, "ax"

 #ifdef CONFIG_FRAME_POINTER
 /* Save parent and function stack frames (rip and rbp) */
 #  define MCOUNT_FRAME_SIZE	(8+16*2)
 #else
 /* No need to save a stack frame */
 # define MCOUNT_FRAME_SIZE	0
 #endif /* CONFIG_FRAME_POINTER */

 /* Size of stack used to save mcount regs in save_mcount_regs */
 #define MCOUNT_REG_SIZE		(FRAME_SIZE + MCOUNT_FRAME_SIZE)

 /*
  * gcc -pg option adds a call to 'mcount' in most functions.
  * When -mfentry is used, the call is to 'fentry' and not 'mcount'
  * and is done before the function's stack frame is set up.
  * They both require a set of regs to be saved before calling
  * any C code and restored before returning back to the function.
  *
  * On boot up, all these calls are converted into nops. When tracing
  * is enabled, the call can jump to either ftrace_caller or
  * ftrace_regs_caller. Callbacks (tracing functions) that require
  * ftrace_regs_caller (like kprobes) need to have pt_regs passed to
  * it. For this reason, the size of the pt_regs structure will be
  * allocated on the stack and the required mcount registers will
  * be saved in the locations that pt_regs has them in.
  */

 /*
  * @added: the amount of stack added before calling this
  *
  * After this is called, the following registers contain:
  *
  *  %rdi - holds the address that called the trampoline
  *  %rsi - holds the parent function (traced function's return address)
  *  %rdx - holds the original %rbp
  */
 .macro save_mcount_regs added=0

 #ifdef CONFIG_FRAME_POINTER
 	/* Save the original rbp */
 	pushq %rbp

 	/*
 	 * Stack traces will stop at the ftrace trampoline if the frame pointer
 	 * is not set up properly. If fentry is used, we need to save a frame
 	 * pointer for the parent as well as the function traced, because the
 	 * fentry is called before the stack frame is set up, where as mcount
 	 * is called afterward.
 	 */

 	/* Save the parent pointer (skip orig rbp and our return address) */
 	pushq \added+8*2(%rsp)
 	pushq %rbp
 	movq %rsp, %rbp
 	/* Save the return address (now skip orig rbp, rbp and parent) */
 	pushq \added+8*3(%rsp)
 	pushq %rbp
 	movq %rsp, %rbp
 #endif /* CONFIG_FRAME_POINTER */

 	/*
 	 * We add enough stack to save all regs.
 	 */
 	subq $(FRAME_SIZE), %rsp
 	movq %rax, RAX(%rsp)
 	movq %rcx, RCX(%rsp)
 	movq %rdx, RDX(%rsp)
 	movq %rsi, RSI(%rsp)
 	movq %rdi, RDI(%rsp)
 	movq %r8, R8(%rsp)
 	movq %r9, R9(%rsp)
 	movq $0, ORIG_RAX(%rsp)
 	/*
 	 * Save the original RBP. Even though the mcount ABI does not
 	 * require this, it helps out callers.
 	 */
 #ifdef CONFIG_FRAME_POINTER
 	movq MCOUNT_REG_SIZE-8(%rsp), %rdx
 #else
 	movq %rbp, %rdx
 #endif
 	movq %rdx, RBP(%rsp)

 	/* Copy the parent address into %rsi (second parameter) */
 	movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi

 	 /* Move RIP to its proper location */
 	movq MCOUNT_REG_SIZE+\added(%rsp), %rdi
 	movq %rdi, RIP(%rsp)

 	/*
 	 * Now %rdi (the first parameter) has the return address of
 	 * where ftrace_call returns. But the callbacks expect the
 	 * address of the call itself.
 	 */
 	subq $MCOUNT_INSN_SIZE, %rdi
 	.endm

 .macro restore_mcount_regs save=0

 	/* ftrace_regs_caller or frame pointers require this */
 	movq RBP(%rsp), %rbp

 	movq R9(%rsp), %r9
 	movq R8(%rsp), %r8
 	movq RDI(%rsp), %rdi
 	movq RSI(%rsp), %rsi
 	movq RDX(%rsp), %rdx
 	movq RCX(%rsp), %rcx
 	movq RAX(%rsp), %rax

 	addq $MCOUNT_REG_SIZE-\save, %rsp

 	.endm

 SYM_TYPED_FUNC_START(ftrace_stub)
 	CALL_DEPTH_ACCOUNT
 	RET
 SYM_FUNC_END(ftrace_stub)

 SYM_TYPED_FUNC_START(ftrace_stub_graph)
 	CALL_DEPTH_ACCOUNT
 	RET
 SYM_FUNC_END(ftrace_stub_graph)

 #ifdef CONFIG_DYNAMIC_FTRACE

 SYM_FUNC_START(__fentry__)
 	CALL_DEPTH_ACCOUNT
 	RET
 SYM_FUNC_END(__fentry__)
 EXPORT_SYMBOL(__fentry__)

 SYM_FUNC_START(ftrace_caller)
 	/* save_mcount_regs fills in first two parameters */
 	save_mcount_regs

 	CALL_DEPTH_ACCOUNT

 	/* Stack - skipping return address of ftrace_caller */
 	leaq MCOUNT_REG_SIZE+8(%rsp), %rcx
 	movq %rcx, RSP(%rsp)

 SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	/* Load the ftrace_ops into the 3rd parameter */
 	movq function_trace_op(%rip), %rdx

 	/* regs go into 4th parameter */
 	leaq (%rsp), %rcx

 	/* Only ops with REGS flag set should have CS register set */
 	movq $0, CS(%rsp)

 	/* Account for the function call below */
 	CALL_DEPTH_ACCOUNT

 SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	call ftrace_stub

 	/* Handlers can change the RIP */
 	movq RIP(%rsp), %rax
 	movq %rax, MCOUNT_REG_SIZE(%rsp)

 	restore_mcount_regs

 	/*
 	 * The code up to this label is copied into trampolines so
 	 * think twice before adding any new code or changing the
 	 * layout here.
 	 */
 SYM_INNER_LABEL(ftrace_caller_end, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	RET
 SYM_FUNC_END(ftrace_caller);
 STACK_FRAME_NON_STANDARD_FP(ftrace_caller)

 SYM_FUNC_START(ftrace_regs_caller)
 	/* Save the current flags before any operations that can change them */
 	pushfq

 	/* added 8 bytes to save flags */
 	save_mcount_regs 8
 	/* save_mcount_regs fills in first two parameters */

 	CALL_DEPTH_ACCOUNT

 SYM_INNER_LABEL(ftrace_regs_caller_op_ptr, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	/* Load the ftrace_ops into the 3rd parameter */
 	movq function_trace_op(%rip), %rdx

 	/* Save the rest of pt_regs */
 	movq %r15, R15(%rsp)
 	movq %r14, R14(%rsp)
 	movq %r13, R13(%rsp)
 	movq %r12, R12(%rsp)
 	movq %r11, R11(%rsp)
 	movq %r10, R10(%rsp)
 	movq %rbx, RBX(%rsp)
 	/* Copy saved flags */
 	movq MCOUNT_REG_SIZE(%rsp), %rcx
 	movq %rcx, EFLAGS(%rsp)
 	/* Kernel segments */
 	movq $__KERNEL_DS, %rcx
 	movq %rcx, SS(%rsp)
 	movq $__KERNEL_CS, %rcx
 	movq %rcx, CS(%rsp)
 	/* Stack - skipping return address and flags */
 	leaq MCOUNT_REG_SIZE+8*2(%rsp), %rcx
 	movq %rcx, RSP(%rsp)

 	ENCODE_FRAME_POINTER

 	/* regs go into 4th parameter */
 	leaq (%rsp), %rcx

 	/* Account for the function call below */
 	CALL_DEPTH_ACCOUNT

 SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	call ftrace_stub

 	/* Copy flags back to SS, to restore them */
 	movq EFLAGS(%rsp), %rax
 	movq %rax, MCOUNT_REG_SIZE(%rsp)

 	/* Handlers can change the RIP */
 	movq RIP(%rsp), %rax
 	movq %rax, MCOUNT_REG_SIZE+8(%rsp)

 	/* restore the rest of pt_regs */
 	movq R15(%rsp), %r15
 	movq R14(%rsp), %r14
 	movq R13(%rsp), %r13
 	movq R12(%rsp), %r12
 	movq R10(%rsp), %r10
 	movq RBX(%rsp), %rbx

 	movq ORIG_RAX(%rsp), %rax
 	movq %rax, MCOUNT_REG_SIZE-8(%rsp)

 	/*
 	 * If ORIG_RAX is anything but zero, make this a call to that.
 	 * See arch_ftrace_set_direct_caller().
 	 */
 	testq	%rax, %rax
 SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	jnz	1f

 	restore_mcount_regs
 	/* Restore flags */
 	popfq

 	/*
 	 * The trampoline will add the return.
 	 */
 SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
 	ANNOTATE_NOENDBR
 	RET

 	/* Swap the flags with orig_rax */
 1:	movq MCOUNT_REG_SIZE(%rsp), %rdi
 	movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
 	movq %rax, MCOUNT_REG_SIZE(%rsp)

 	restore_mcount_regs 8
 	/* Restore flags */
 	popfq
 	UNWIND_HINT_FUNC

 	/*
 	 * The above left an extra return value on the stack; effectively
 	 * doing a tail-call without using a register. This PUSH;RET
 	 * pattern unbalances the RSB, inject a pointless CALL to rebalance.
 	 */
 	ANNOTATE_INTRA_FUNCTION_CALL
 	CALL .Ldo_rebalance
 	int3
 .Ldo_rebalance:
 	add $8, %rsp
 	ALTERNATIVE __stringify(RET), \
 		    __stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
 		    X86_FEATURE_CALL_DEPTH

 SYM_FUNC_END(ftrace_regs_caller)
 STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)


 #else /* ! CONFIG_DYNAMIC_FTRACE */

 SYM_FUNC_START(__fentry__)
 	CALL_DEPTH_ACCOUNT

 	cmpq $ftrace_stub, ftrace_trace_function
 	jnz trace
 	RET

 trace:
 	/* save_mcount_regs fills in first two parameters */
 	save_mcount_regs

 	/*
 	 * When DYNAMIC_FTRACE is not defined, ARCH_SUPPORTS_FTRACE_OPS is not
 	 * set (see include/asm/ftrace.h and include/linux/ftrace.h).  Only the
 	 * ip and parent ip are used and the list function is called when
 	 * function tracing is enabled.
 	 */
 	movq ftrace_trace_function, %r8
 	CALL_NOSPEC r8
 	restore_mcount_regs

 	jmp ftrace_stub
 SYM_FUNC_END(__fentry__)
 EXPORT_SYMBOL(__fentry__)
 STACK_FRAME_NON_STANDARD_FP(__fentry__)

 #endif /* CONFIG_DYNAMIC_FTRACE */

 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 SYM_CODE_START(return_to_handler)
 	UNWIND_HINT_EMPTY
 	ANNOTATE_NOENDBR
 	subq  $16, %rsp

 	/* Save the return values */
 	movq %rax, (%rsp)
 	movq %rdx, 8(%rsp)
 	movq %rbp, %rdi

 	call ftrace_return_to_handler

 	movq %rax, %rdi
 	movq 8(%rsp), %rdx
 	movq (%rsp), %rax

 	addq $16, %rsp
 	/*
 	 * Jump back to the old return address. This cannot be JMP_NOSPEC rdi
 	 * since IBT would demand that contain ENDBR, which simply isn't so for
 	 * return addresses. Use a retpoline here to keep the RSB balanced.
 	 */
 	ANNOTATE_INTRA_FUNCTION_CALL
 	call .Ldo_rop
 	int3
 .Ldo_rop:
 	mov %rdi, (%rsp)
 	ALTERNATIVE __stringify(RET), \
 		    __stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
 		    X86_FEATURE_CALL_DEPTH
 SYM_CODE_END(return_to_handler)
 #endif
	/* SPDX-License-Identifier: GPL-2.0 */
	/*
	* Copyright (C) 2014 Steven Rostedt, Red Hat Inc
	*/

	#include <linux/cfi_types.h>
	#include <linux/linkage.h>
	#include <asm/asm-offsets.h>
	#include <asm/ptrace.h>
	#include <asm/ftrace.h>
	#include <asm/export.h>
	#include <asm/nospec-branch.h>
	#include <asm/unwind_hints.h>
	#include <asm/frame.h>

	.code64
	.section .text, "ax"

	#ifdef CONFIG_FRAME_POINTER
	/* Save parent and function stack frames (rip and rbp) */
	# define MCOUNT_FRAME_SIZE (8+16*2)
	#else
	/* No need to save a stack frame */
	# define MCOUNT_FRAME_SIZE 0
	#endif /* CONFIG_FRAME_POINTER */

	/* Size of stack used to save mcount regs in save_mcount_regs */
	#define MCOUNT_REG_SIZE (FRAME_SIZE + MCOUNT_FRAME_SIZE)

	/*
	* gcc -pg option adds a call to 'mcount' in most functions.
	* When -mfentry is used, the call is to 'fentry' and not 'mcount'
	* and is done before the function's stack frame is set up.
	* They both require a set of regs to be saved before calling
	* any C code and restored before returning back to the function.
	*
	* On boot up, all these calls are converted into nops. When tracing
	* is enabled, the call can jump to either ftrace_caller or
	* ftrace_regs_caller. Callbacks (tracing functions) that require
	* ftrace_regs_caller (like kprobes) need to have pt_regs passed to
	* it. For this reason, the size of the pt_regs structure will be
	* allocated on the stack and the required mcount registers will
	* be saved in the locations that pt_regs has them in.
	*/

	/*
	* @added: the amount of stack added before calling this
	*
	* After this is called, the following registers contain:
	*
	* %rdi - holds the address that called the trampoline
	* %rsi - holds the parent function (traced function's return address)
	* %rdx - holds the original %rbp
	*/
	.macro save_mcount_regs added=0

	#ifdef CONFIG_FRAME_POINTER
	/* Save the original rbp */
	pushq %rbp

	/*
	* Stack traces will stop at the ftrace trampoline if the frame pointer
	* is not set up properly. If fentry is used, we need to save a frame
	* pointer for the parent as well as the function traced, because the
	* fentry is called before the stack frame is set up, where as mcount
	* is called afterward.
	*/

	/* Save the parent pointer (skip orig rbp and our return address) */
	pushq \added+8*2(%rsp)
	pushq %rbp
	movq %rsp, %rbp
	/* Save the return address (now skip orig rbp, rbp and parent) */
	pushq \added+8*3(%rsp)
	pushq %rbp
	movq %rsp, %rbp
	#endif /* CONFIG_FRAME_POINTER */

	/*
	* We add enough stack to save all regs.
	*/
	subq $(FRAME_SIZE), %rsp
	movq %rax, RAX(%rsp)
	movq %rcx, RCX(%rsp)
	movq %rdx, RDX(%rsp)
	movq %rsi, RSI(%rsp)
	movq %rdi, RDI(%rsp)
	movq %r8, R8(%rsp)
	movq %r9, R9(%rsp)
	movq $0, ORIG_RAX(%rsp)
	/*
	* Save the original RBP. Even though the mcount ABI does not
	* require this, it helps out callers.
	*/
	#ifdef CONFIG_FRAME_POINTER
	movq MCOUNT_REG_SIZE-8(%rsp), %rdx
	#else
	movq %rbp, %rdx
	#endif
	movq %rdx, RBP(%rsp)

	/* Copy the parent address into %rsi (second parameter) */
	movq MCOUNT_REG_SIZE+8+\added(%rsp), %rsi

	/* Move RIP to its proper location */
	movq MCOUNT_REG_SIZE+\added(%rsp), %rdi
	movq %rdi, RIP(%rsp)

	/*
	* Now %rdi (the first parameter) has the return address of
	* where ftrace_call returns. But the callbacks expect the
	* address of the call itself.
	*/
	subq $MCOUNT_INSN_SIZE, %rdi
	.endm

	.macro restore_mcount_regs save=0

	/* ftrace_regs_caller or frame pointers require this */
	movq RBP(%rsp), %rbp

	movq R9(%rsp), %r9
	movq R8(%rsp), %r8
	movq RDI(%rsp), %rdi
	movq RSI(%rsp), %rsi
	movq RDX(%rsp), %rdx
	movq RCX(%rsp), %rcx
	movq RAX(%rsp), %rax

	addq $MCOUNT_REG_SIZE-\save, %rsp

	.endm

	SYM_TYPED_FUNC_START(ftrace_stub)
	CALL_DEPTH_ACCOUNT
	RET
	SYM_FUNC_END(ftrace_stub)

	SYM_TYPED_FUNC_START(ftrace_stub_graph)
	CALL_DEPTH_ACCOUNT
	RET
	SYM_FUNC_END(ftrace_stub_graph)

	#ifdef CONFIG_DYNAMIC_FTRACE

	SYM_FUNC_START(__fentry__)
	CALL_DEPTH_ACCOUNT
	RET
	SYM_FUNC_END(__fentry__)
	EXPORT_SYMBOL(__fentry__)

	SYM_FUNC_START(ftrace_caller)
	/* save_mcount_regs fills in first two parameters */
	save_mcount_regs

	CALL_DEPTH_ACCOUNT

	/* Stack - skipping return address of ftrace_caller */
	leaq MCOUNT_REG_SIZE+8(%rsp), %rcx
	movq %rcx, RSP(%rsp)

	SYM_INNER_LABEL(ftrace_caller_op_ptr, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	/* Load the ftrace_ops into the 3rd parameter */
	movq function_trace_op(%rip), %rdx

	/* regs go into 4th parameter */
	leaq (%rsp), %rcx

	/* Only ops with REGS flag set should have CS register set */
	movq $0, CS(%rsp)

	/* Account for the function call below */
	CALL_DEPTH_ACCOUNT

	SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	call ftrace_stub

	/* Handlers can change the RIP */
	movq RIP(%rsp), %rax
	movq %rax, MCOUNT_REG_SIZE(%rsp)

	restore_mcount_regs

	/*
	* The code up to this label is copied into trampolines so
	* think twice before adding any new code or changing the
	* layout here.
	*/
	SYM_INNER_LABEL(ftrace_caller_end, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	RET
	SYM_FUNC_END(ftrace_caller);
	STACK_FRAME_NON_STANDARD_FP(ftrace_caller)

	SYM_FUNC_START(ftrace_regs_caller)
	/* Save the current flags before any operations that can change them */
	pushfq

	/* added 8 bytes to save flags */
	save_mcount_regs 8
	/* save_mcount_regs fills in first two parameters */

	CALL_DEPTH_ACCOUNT

	SYM_INNER_LABEL(ftrace_regs_caller_op_ptr, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	/* Load the ftrace_ops into the 3rd parameter */
	movq function_trace_op(%rip), %rdx

	/* Save the rest of pt_regs */
	movq %r15, R15(%rsp)
	movq %r14, R14(%rsp)
	movq %r13, R13(%rsp)
	movq %r12, R12(%rsp)
	movq %r11, R11(%rsp)
	movq %r10, R10(%rsp)
	movq %rbx, RBX(%rsp)
	/* Copy saved flags */
	movq MCOUNT_REG_SIZE(%rsp), %rcx
	movq %rcx, EFLAGS(%rsp)
	/* Kernel segments */
	movq $__KERNEL_DS, %rcx
	movq %rcx, SS(%rsp)
	movq $__KERNEL_CS, %rcx
	movq %rcx, CS(%rsp)
	/* Stack - skipping return address and flags */
	leaq MCOUNT_REG_SIZE+8*2(%rsp), %rcx
	movq %rcx, RSP(%rsp)

	ENCODE_FRAME_POINTER

	/* regs go into 4th parameter */
	leaq (%rsp), %rcx

	/* Account for the function call below */
	CALL_DEPTH_ACCOUNT

	SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	call ftrace_stub

	/* Copy flags back to SS, to restore them */
	movq EFLAGS(%rsp), %rax
	movq %rax, MCOUNT_REG_SIZE(%rsp)

	/* Handlers can change the RIP */
	movq RIP(%rsp), %rax
	movq %rax, MCOUNT_REG_SIZE+8(%rsp)

	/* restore the rest of pt_regs */
	movq R15(%rsp), %r15
	movq R14(%rsp), %r14
	movq R13(%rsp), %r13
	movq R12(%rsp), %r12
	movq R10(%rsp), %r10
	movq RBX(%rsp), %rbx

	movq ORIG_RAX(%rsp), %rax
	movq %rax, MCOUNT_REG_SIZE-8(%rsp)

	/*
	* If ORIG_RAX is anything but zero, make this a call to that.
	* See arch_ftrace_set_direct_caller().
	*/
	testq %rax, %rax
	SYM_INNER_LABEL(ftrace_regs_caller_jmp, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	jnz 1f

	restore_mcount_regs
	/* Restore flags */
	popfq

	/*
	* The trampoline will add the return.
	*/
	SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
	ANNOTATE_NOENDBR
	RET

	/* Swap the flags with orig_rax */
	1: movq MCOUNT_REG_SIZE(%rsp), %rdi
	movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
	movq %rax, MCOUNT_REG_SIZE(%rsp)

	restore_mcount_regs 8
	/* Restore flags */
	popfq
	UNWIND_HINT_FUNC

	/*
	* The above left an extra return value on the stack; effectively
	* doing a tail-call without using a register. This PUSH;RET
	* pattern unbalances the RSB, inject a pointless CALL to rebalance.
	*/
	ANNOTATE_INTRA_FUNCTION_CALL
	CALL .Ldo_rebalance
	int3
	.Ldo_rebalance:
	add $8, %rsp
	ALTERNATIVE __stringify(RET), \
	__stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
	X86_FEATURE_CALL_DEPTH

	SYM_FUNC_END(ftrace_regs_caller)
	STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)


	#else /* ! CONFIG_DYNAMIC_FTRACE */

	SYM_FUNC_START(__fentry__)
	CALL_DEPTH_ACCOUNT

	cmpq $ftrace_stub, ftrace_trace_function
	jnz trace
	RET

	trace:
	/* save_mcount_regs fills in first two parameters */
	save_mcount_regs

	/*
	* When DYNAMIC_FTRACE is not defined, ARCH_SUPPORTS_FTRACE_OPS is not
	* set (see include/asm/ftrace.h and include/linux/ftrace.h). Only the
	* ip and parent ip are used and the list function is called when
	* function tracing is enabled.
	*/
	movq ftrace_trace_function, %r8
	CALL_NOSPEC r8
	restore_mcount_regs

	jmp ftrace_stub
	SYM_FUNC_END(__fentry__)
	EXPORT_SYMBOL(__fentry__)
	STACK_FRAME_NON_STANDARD_FP(__fentry__)

	#endif /* CONFIG_DYNAMIC_FTRACE */

	#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	SYM_CODE_START(return_to_handler)
	UNWIND_HINT_EMPTY
	ANNOTATE_NOENDBR
	subq $16, %rsp

	/* Save the return values */
	movq %rax, (%rsp)
	movq %rdx, 8(%rsp)
	movq %rbp, %rdi

	call ftrace_return_to_handler

	movq %rax, %rdi
	movq 8(%rsp), %rdx
	movq (%rsp), %rax

	addq $16, %rsp
	/*
	* Jump back to the old return address. This cannot be JMP_NOSPEC rdi
	* since IBT would demand that contain ENDBR, which simply isn't so for
	* return addresses. Use a retpoline here to keep the RSB balanced.
	*/
	ANNOTATE_INTRA_FUNCTION_CALL
	call .Ldo_rop
	int3
	.Ldo_rop:
	mov %rdi, (%rsp)
	ALTERNATIVE __stringify(RET), \
	__stringify(ANNOTATE_UNRET_SAFE; ret; int3), \
	X86_FEATURE_CALL_DEPTH
	SYM_CODE_END(return_to_handler)
	#endif