tracing, x86: add low level support for ftrace return tracing

Impact: add infrastructure for function-return tracing

Add low level support for ftrace return tracing.

This plug-in stores return addresses on the thread_info structure of
the current task.

The index of the current return address is initialized when the task
is the first one (init) and when a process forks (the child). It is
not needed when a task does a sys_execve because after this syscall,
it still needs to return on the kernel functions it called.

Note that the code of return_to_handler has been suggested by Steven
Rostedt as almost all of the ideas of improvements in this V3.

For purpose of security, arch/x86/kernel/process_32.c is not traced
because __switch_to() changes the current task during its execution.
That could cause inconsistency in the stored return address of this
function even if I didn't have any crash after testing with tracing on
this function enabled.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index e489ff9cb3e2..1d8ed95da846 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -14,6 +14,11 @@ CFLAGS_REMOVE_paravirt-spinlocks.o = -pg
 CFLAGS_REMOVE_ftrace.o = -pg
 endif
 
+ifdef CONFIG_FUNCTION_RET_TRACER
+# Don't trace __switch_to() but let it for function tracer
+CFLAGS_REMOVE_process_32.o = -pg
+endif
+
 #
 # vsyscalls (which work on the user stack) should have
 # no stack-protector checks:
@@ -65,6 +70,7 @@ obj-$(CONFIG_X86_LOCAL_APIC)	+= apic.o nmi.o
 obj-$(CONFIG_X86_IO_APIC)       += io_apic.o
 obj-$(CONFIG_X86_REBOOTFIXUPS)  += reboot_fixups_32.o
 obj-$(CONFIG_DYNAMIC_FTRACE)    += ftrace.o
+obj-$(CONFIG_FUNCTION_RET_TRACER)       += ftrace.o
 obj-$(CONFIG_KEXEC)             += machine_kexec_$(BITS).o
 obj-$(CONFIG_KEXEC)             += relocate_kernel_$(BITS).o crash.o
 obj-$(CONFIG_CRASH_DUMP)        += crash_dump_$(BITS).o