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Commit 644e0e8d authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware) Committed by Thomas Gleixner
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x86/ftrace: Add -mfentry support to x86_32 with DYNAMIC_FTRACE set 



x86_64 has had fentry support for some time. I did not add support to x86_32
as I was unsure if it will be used much in the future. It is still very much
used, and there's issues with function graph tracing with gcc playing around
with the mcount frames, causing function graph to panic. The fentry code
does not have this issue, and is able to cope as there is no frame to mess
up.

Note, this only adds support for fentry when DYNAMIC_FTRACE is set. There's
really no reason to not have that set, because the performance of the
machine drops significantly when it's not enabled.

Keep !DYNAMIC_FTRACE around to test it off, as there's still some archs
that have FTRACE but not DYNAMIC_FTRACE.

Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
Reviewed-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: default avatarIngo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/20170323143446.052202377@goodmis.org


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent ff04b440

arch/x86/Kconfig

+1 −1
Original line number Diff line number Diff line
@@ -127,7 +127,7 @@ config X86 
	select HAVE_EBPF_JIT			if X86_64

	select HAVE_EFFICIENT_UNALIGNED_ACCESS

	select HAVE_EXIT_THREAD

	select HAVE_FENTRY			if X86_64

	select HAVE_FENTRY			if X86_64 || DYNAMIC_FTRACE

	select HAVE_FTRACE_MCOUNT_RECORD

	select HAVE_FUNCTION_GRAPH_TRACER

	select HAVE_FUNCTION_TRACER

arch/x86/kernel/ftrace_32.S

+72 −10
Original line number Diff line number Diff line
@@ -9,26 +9,68 @@ 
#include <asm/ftrace.h>



#ifdef CONFIG_FUNCTION_TRACER



#ifdef CC_USING_FENTRY

# define function_hook	__fentry__

EXPORT_SYMBOL(__fentry__)

#else

# define function_hook	mcount

EXPORT_SYMBOL(mcount)

#endif



#ifdef CONFIG_DYNAMIC_FTRACE



ENTRY(mcount)

/* 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

#endif



#ifdef USING_FRAME_POINTER

# define MCOUNT_FRAME			1	/* using frame = true  */

#else

# define MCOUNT_FRAME			0	/* using frame = false */

#endif



ENTRY(function_hook)

	ret

END(mcount)

END(function_hook)



ENTRY(ftrace_caller)



#ifdef USING_FRAME_POINTER

# ifdef CC_USING_FENTRY

	/*

	 * Frame pointers are of ip followed by bp.

	 * Since fentry is an immediate jump, we are left with

	 * parent-ip, function-ip. We need to add a frame with

	 * parent-ip followed by ebp.

	 */

	pushl	4(%esp)				/* parent ip */

	pushl	%ebp

	movl	%esp, %ebp



	pushl	2*4(%esp)			/* function ip */

# endif

	/* For mcount, the function ip is directly above */

	pushl	%ebp

	movl	%esp, %ebp

#endif

	pushl	%eax

	pushl	%ecx

	pushl	%edx

	pushl	$0				/* Pass NULL as regs pointer */

	movl	5*4(%esp), %eax

	/* Copy original ebp into %edx */



#ifdef USING_FRAME_POINTER

	/* Load parent ebp into edx */

	movl	4*4(%esp), %edx

#else

	/* There's no frame pointer, load the appropriate stack addr instead */

	lea	4*4(%esp), %edx

#endif



	movl	(MCOUNT_FRAME+4)*4(%esp), %eax	/* load the rip */

	/* Get the parent ip */

	movl	0x4(%edx), %edx

	movl	4(%edx), %edx			/* edx has ebp */



	movl	function_trace_op, %ecx

	subl	$MCOUNT_INSN_SIZE, %eax
@@ -40,7 +82,14 @@ ftrace_call: 
	popl	%edx

	popl	%ecx

	popl	%eax

#ifdef USING_FRAME_POINTER

	popl	%ebp

# ifdef CC_USING_FENTRY

	addl	$4,%esp				/* skip function ip */

	popl	%ebp				/* this is the orig bp */

	addl	$4, %esp			/* skip parent ip */

# endif

#endif

.Lftrace_ret:

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

.globl ftrace_graph_call
@@ -81,6 +130,10 @@ ENTRY(ftrace_regs_caller) 
	pushl	%edx

	pushl	%ecx

	pushl	%ebx

#ifdef CC_USING_FENTRY

	/* Load 4 off of the parent ip addr into ebp */

	lea	14*4(%esp), %ebp

#endif



	movl	12*4(%esp), %eax		/* Load ip (1st parameter) */

	subl	$MCOUNT_INSN_SIZE, %eax		/* Adjust ip */
@@ -119,7 +172,7 @@ GLOBAL(ftrace_regs_call) 
	jmp	.Lftrace_ret

#else /* ! CONFIG_DYNAMIC_FTRACE */



ENTRY(mcount)

ENTRY(function_hook)

	cmpl	$__PAGE_OFFSET, %esp

	jb	ftrace_stub			/* Paging not enabled yet? */
@@ -151,9 +204,8 @@ ftrace_stub: 
	popl	%ecx

	popl	%eax

	jmp	ftrace_stub

END(mcount)

END(function_hook)

#endif /* CONFIG_DYNAMIC_FTRACE */

EXPORT_SYMBOL(mcount)

#endif /* CONFIG_FUNCTION_TRACER */



#ifdef CONFIG_FUNCTION_GRAPH_TRACER
@@ -161,9 +213,15 @@ ENTRY(ftrace_graph_caller) 
	pushl	%eax

	pushl	%ecx

	pushl	%edx

	movl	0xc(%esp), %eax

	movl	3*4(%esp), %eax

	/* Even with frame pointers, fentry doesn't have one here */

#ifdef CC_USING_FENTRY

	lea	4*4(%esp), %edx

	movl	$0, %ecx

#else

	lea	0x4(%ebp), %edx

	movl	(%ebp), %ecx

#endif

	subl	$MCOUNT_INSN_SIZE, %eax

	call	prepare_ftrace_return

	popl	%edx
@@ -176,7 +234,11 @@ END(ftrace_graph_caller) 
return_to_handler:

	pushl	%eax

	pushl	%edx

#ifdef CC_USING_FENTRY

	movl	$0, %eax

#else

	movl	%ebp, %eax

#endif

	call	ftrace_return_to_handler

	movl	%eax, %ecx

	popl	%edx