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Commit 518049d9 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware)
Browse files

ftrace/x86_32: Remove support for non DYNAMIC_FTRACE 



When DYNAMIC_FTRACE is enabled in the kernel, all the functions that can be
traced by the function tracer have a "nop" placeholder at the start of the
function. When function tracing is enabled, the nop is converted into a call
to the tracing infrastructure where the functions get traced. This also
allows for specifying specific functions to trace, and a lot of
infrastructure is built on top of this.

When DYNAMIC_FTRACE is not enabled, all the functions have a call to the
ftrace trampoline. A check is made to see if a function pointer is the
ftrace_stub or not, and if it is not, it calls the function pointer to trace
the code. This adds over 10% overhead to the kernel even when tracing is
disabled.

When an architecture supports DYNAMIC_FTRACE there really is no reason to
use the static tracing. I have kept non DYNAMIC_FTRACE available in x86 so
that the generic code for non DYNAMIC_FTRACE can be tested. There is no
reason to support non DYNAMIC_FTRACE for both x86_64 and x86_32. As the non
DYNAMIC_FTRACE for x86_32 does not even support fentry, and we want to
remove mcount completely, there's no reason to keep non DYNAMIC_FTRACE
around for x86_32.

Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent a15fd609

arch/x86/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -31,6 +31,17 @@ config X86_64 
	select X86_DEV_DMA_OPS

	select ARCH_HAS_SYSCALL_WRAPPER



config FORCE_DYNAMIC_FTRACE

	def_bool y

	depends on X86_32

	depends on FUNCTION_TRACER

	select DYNAMIC_FTRACE

	help

	 We keep the static function tracing (!DYNAMIC_FTRACE) around

	 in order to test the non static function tracing in the

	 generic code, as other architectures still use it. But we

	 only need to keep it around for x86_64. No need to keep it

	 for x86_32. For x86_32, force DYNAMIC_FTRACE. 

#

# Arch settings

#

arch/x86/kernel/ftrace_32.S

+0 −39
Original line number Diff line number Diff line
@@ -18,8 +18,6 @@ EXPORT_SYMBOL(__fentry__) 
EXPORT_SYMBOL(mcount)

#endif



#ifdef CONFIG_DYNAMIC_FTRACE



/* mcount uses a frame pointer even if CONFIG_FRAME_POINTER is not set */

#if !defined(CC_USING_FENTRY) || defined(CONFIG_FRAME_POINTER)

# define USING_FRAME_POINTER
@@ -170,43 +168,6 @@ GLOBAL(ftrace_regs_call) 
	lea	3*4(%esp), %esp			/* Skip orig_ax, ip and cs */



	jmp	.Lftrace_ret

#else /* ! CONFIG_DYNAMIC_FTRACE */



ENTRY(function_hook)

	cmpl	$__PAGE_OFFSET, %esp

	jb	ftrace_stub			/* Paging not enabled yet? */



	cmpl	$ftrace_stub, ftrace_trace_function

	jnz	.Ltrace

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

	cmpl	$ftrace_stub, ftrace_graph_return

	jnz	ftrace_graph_caller



	cmpl	$ftrace_graph_entry_stub, ftrace_graph_entry

	jnz	ftrace_graph_caller

#endif

.globl ftrace_stub

ftrace_stub:

	ret



	/* taken from glibc */

.Ltrace:

	pushl	%eax

	pushl	%ecx

	pushl	%edx

	movl	0xc(%esp), %eax

	movl	0x4(%ebp), %edx

	subl	$MCOUNT_INSN_SIZE, %eax



	movl	ftrace_trace_function, %ecx

	CALL_NOSPEC %ecx



	popl	%edx

	popl	%ecx

	popl	%eax

	jmp	ftrace_stub

END(function_hook)

#endif /* CONFIG_DYNAMIC_FTRACE */



#ifdef CONFIG_FUNCTION_GRAPH_TRACER

ENTRY(ftrace_graph_caller)