tracing/function-graph-tracer: support for x86-64

Impact: extend and enable the function graph tracer to 64-bit x86

This patch implements the support for function graph tracer under x86-64.
Both static and dynamic tracing are supported.

This causes some small CPP conditional asm on arch/x86/kernel/ftrace.c I
wanted to use probe_kernel_read/write to make the return address
saving/patching code more generic but it causes tracing recursion.

That would be perhaps useful to implement a notrace version of these
function for other archs ports.

Note that arch/x86/process_64.c is not traced, as in X86-32. I first
thought __switch_to() was responsible of crashes during tracing because I
believed current task were changed inside but that's actually not the
case (actually yes, but not the "current" pointer).

So I will have to investigate to find the functions that harm here, to
enable tracing of the other functions inside (but there is no issue at
this time, while process_64.c stays out of -pg flags).

A little possible race condition is fixed inside this patch too. When the
tracer allocate a return stack dynamically, the current depth is not
initialized before but after. An interrupt could occur at this time and,
after seeing that the return stack is allocated, the tracer could try to
trace it with a random uninitialized depth. It's a prevention, even if I
hadn't problems with it.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tim Bird <tim.bird@am.sony.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/Kconfig

@@ -29,7 +29,7 @@ config X86
 	select HAVE_FTRACE_MCOUNT_RECORD
 	select HAVE_DYNAMIC_FTRACE
 	select HAVE_FUNCTION_TRACER
-	select HAVE_FUNCTION_GRAPH_TRACER if X86_32
+	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACE_MCOUNT_TEST
 	select HAVE_KVM if ((X86_32 && !X86_VOYAGER && !X86_VISWS && !X86_NUMAQ) || X86_64)
 	select HAVE_ARCH_KGDB if !X86_VOYAGER

arch/x86/kernel/Makefile

@@ -17,6 +17,7 @@ endif
 ifdef CONFIG_FUNCTION_GRAPH_TRACER
 # Don't trace __switch_to() but let it for function tracer
 CFLAGS_REMOVE_process_32.o = -pg
+CFLAGS_REMOVE_process_64.o = -pg
 endif
 
 #

arch/x86/kernel/entry_64.S

@@ -98,6 +98,12 @@ ftrace_call:
 	movq (%rsp), %rax
 	addq $0x38, %rsp
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+.globl ftrace_graph_call
+ftrace_graph_call:
+	jmp ftrace_stub
+#endif
+
 .globl ftrace_stub
 ftrace_stub:
 	retq
@@ -110,6 +116,12 @@ ENTRY(mcount)
 
 	cmpq $ftrace_stub, ftrace_trace_function
 	jnz trace
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	cmpq $ftrace_stub, ftrace_graph_return
+	jnz ftrace_graph_caller
+#endif
+
 .globl ftrace_stub
 ftrace_stub:
 	retq
@@ -145,6 +157,68 @@ END(mcount)
 #endif /* CONFIG_DYNAMIC_FTRACE */
 #endif /* CONFIG_FUNCTION_TRACER */
 
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ENTRY(ftrace_graph_caller)
+	cmpl $0, function_trace_stop
+	jne ftrace_stub
+
+	subq $0x38, %rsp
+	movq %rax, (%rsp)
+	movq %rcx, 8(%rsp)
+	movq %rdx, 16(%rsp)
+	movq %rsi, 24(%rsp)
+	movq %rdi, 32(%rsp)
+	movq %r8, 40(%rsp)
+	movq %r9, 48(%rsp)
+
+	leaq 8(%rbp), %rdi
+	movq 0x38(%rsp), %rsi
+
+	call	prepare_ftrace_return
+
+	movq 48(%rsp), %r9
+	movq 40(%rsp), %r8
+	movq 32(%rsp), %rdi
+	movq 24(%rsp), %rsi
+	movq 16(%rsp), %rdx
+	movq 8(%rsp), %rcx
+	movq (%rsp), %rax
+	addq $0x38, %rsp
+	retq
+END(ftrace_graph_caller)
+
+
+.globl return_to_handler
+return_to_handler:
+	subq  $80, %rsp
+
+	movq %rax, (%rsp)
+	movq %rcx, 8(%rsp)
+	movq %rdx, 16(%rsp)
+	movq %rsi, 24(%rsp)
+	movq %rdi, 32(%rsp)
+	movq %r8, 40(%rsp)
+	movq %r9, 48(%rsp)
+	movq %r10, 56(%rsp)
+	movq %r11, 64(%rsp)
+
+	call ftrace_return_to_handler
+
+	movq %rax, 72(%rsp)
+	movq 64(%rsp), %r11
+	movq 56(%rsp), %r10
+	movq 48(%rsp), %r9
+	movq 40(%rsp), %r8
+	movq 32(%rsp), %rdi
+	movq 24(%rsp), %rsi
+	movq 16(%rsp), %rdx
+	movq 8(%rsp), %rcx
+	movq (%rsp), %rax
+	addq $72, %rsp
+	retq
+#endif
+
+
 #ifndef CONFIG_PREEMPT
 #define retint_kernel retint_restore_args
 #endif	

arch/x86/kernel/ftrace.c

@@ -467,17 +467,27 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 	 * ignore such a protection.
 	 */
 	asm volatile(
+#ifdef CONFIG_X86_64
+		"1: movq (%[parent_old]), %[old]\n"
+		"2: movq %[return_hooker], (%[parent_replaced])\n"
+#else
 		"1: movl (%[parent_old]), %[old]\n"
 		"2: movl %[return_hooker], (%[parent_replaced])\n"
+#endif
 		"   movl $0, %[faulted]\n"
 
 		".section .fixup, \"ax\"\n"
 		"3: movl $1, %[faulted]\n"
 		".previous\n"
 
 		".section __ex_table, \"a\"\n"
+#ifdef CONFIG_X86_64
+		"   .quad 1b, 3b\n"
+		"   .quad 2b, 3b\n"
+#else
 		"   .long 1b, 3b\n"
 		"   .long 2b, 3b\n"
+#endif
 		".previous\n"
 
 		: [parent_replaced] "=r" (parent), [old] "=r" (old),
@@ -509,5 +519,4 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
 	ftrace_graph_entry(&trace);
 
 }
-
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */

kernel/trace/ftrace.c

@@ -1673,8 +1673,10 @@ static int alloc_retstack_tasklist(struct ftrace_ret_stack **ret_stack_list)
 		}
 
 		if (t->ret_stack == NULL) {
-			t->ret_stack = ret_stack_list[start++];
 			t->curr_ret_stack = -1;
+			/* Make sure IRQs see the -1 first: */
+			barrier();
+			t->ret_stack = ret_stack_list[start++];
 			atomic_set(&t->trace_overrun, 0);
 		}
 	} while_each_thread(g, t);