x86/ftrace: Implement DYNAMIC_FTRACE_WITH_JMP

Implement the DYNAMIC_FTRACE_WITH_JMP for x86_64. In ftrace_call_replace,
we will use JMP32_INSN_OPCODE instead of CALL_INSN_OPCODE if the address
should use "jmp".

Meanwhile, adjust the direct call in the ftrace_regs_caller. The RSB is
balanced in the "jmp" mode. Take the function "foo" for example:

original_caller:
call foo -> foo:
call fentry -> fentry:
[do ftrace callbacks ]
move tramp_addr to stack
RET -> tramp_addr
tramp_addr:
[..]
call foo_body -> foo_body:
[..]
RET -> back to tramp_addr
[..]
RET -> back to original_caller

Signed-off-by: Menglong Dong <[e-mail]>
Acked-by: Steven Rostedt (Google) <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

arch/x86/Kconfig

···
 	select HAVE_DYNAMIC_FTRACE_WITH_ARGS	if X86_64
 	select HAVE_FTRACE_REGS_HAVING_PT_REGS	if X86_64
 	select HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+	select HAVE_DYNAMIC_FTRACE_WITH_JMP	if X86_64
 	select HAVE_SAMPLE_FTRACE_DIRECT	if X86_64
 	select HAVE_SAMPLE_FTRACE_DIRECT_MULTI	if X86_64
 	select HAVE_EBPF_JIT

arch/x86/kernel/ftrace.c

···
 	 * No need to translate into a callthunk. The trampoline does
 	 * the depth accounting itself.
 	 */
-	return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void *)addr);
+	if (ftrace_is_jmp(addr)) {
+		addr = ftrace_jmp_get(addr);
+		return text_gen_insn(JMP32_INSN_OPCODE, (void *)ip, (void *)addr);
+	} else {
+		return text_gen_insn(CALL_INSN_OPCODE, (void *)ip, (void *)addr);
+	}
 }
 
 static int ftrace_verify_code(unsigned long ip, const char *old_code)

arch/x86/kernel/ftrace_64.S

···
 	ANNOTATE_NOENDBR
 	RET
 
+1:
+	testb	$1, %al
+	jz	2f
+	andq $0xfffffffffffffffe, %rax
+	movq %rax, MCOUNT_REG_SIZE+8(%rsp)
+	restore_mcount_regs
+	/* Restore flags */
+	popfq
+	RET
+
 	/* Swap the flags with orig_rax */
-1:	movq MCOUNT_REG_SIZE(%rsp), %rdi
+2:	movq MCOUNT_REG_SIZE(%rsp), %rdi
 	movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
 	movq %rax, MCOUNT_REG_SIZE(%rsp)