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Commit ff04b440 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware) Committed by Thomas Gleixner
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x86/ftrace: Clean up ftrace_regs_caller 



When ftrace_regs_caller was created, it was designed to preserve flags as
much as possible as it needed to act just like a breakpoint triggered on the
same location. But the design is over complicated as it treated all
operations as modifying flags. But push, mov and lea do not modify flags.
This means the code can become more simplified by allowing flags to be
stored further down.

Making ftrace_regs_caller simpler will also be useful in implementing fentry
logic.

Suggested-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
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>
Link: http://lkml.kernel.org/r/20170316135328.36123c3e@gandalf.local.home
Link: http://lkml.kernel.org/r/20170323143445.917292592@goodmis.org


Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
parent e6928e58

arch/x86/kernel/ftrace_32.S

+21 −19
Original line number Diff line number Diff line
@@ -54,23 +54,27 @@ WEAK(ftrace_stub) 
END(ftrace_caller)



ENTRY(ftrace_regs_caller)

	pushf	/* push flags before compare (in cs location) */



	/*

	 * i386 does not save SS and ESP when coming from kernel.

	 * Instead, to get sp, &regs->sp is used (see ptrace.h).

	 * Unfortunately, that means eflags must be at the same location

	 * as the current return ip is. We move the return ip into the

	 * ip location, and move flags into the return ip location.

	 * regs->ip location, and move flags into the return ip location.

	 */

	pushl	4(%esp)				/* save return ip into ip slot */



	pushl	$__KERNEL_CS

	pushl	4(%esp)				/* Save the return ip */

	pushl	$0				/* Load 0 into orig_ax */

	pushl	%gs

	pushl	%fs

	pushl	%es

	pushl	%ds

	pushl	%eax



	/* Get flags and place them into the return ip slot */

	pushf

	popl	%eax

	movl	%eax, 8*4(%esp)



	pushl	%ebp

	pushl	%edi

	pushl	%esi
@@ -78,11 +82,6 @@ ENTRY(ftrace_regs_caller) 
	pushl	%ecx

	pushl	%ebx



	movl	13*4(%esp), %eax		/* Get the saved flags */

	movl	%eax, 14*4(%esp)		/* Move saved flags into regs->flags location */

						/* clobbering return ip */

	movl	$__KERNEL_CS, 13*4(%esp)



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

	subl	$MCOUNT_INSN_SIZE, %eax		/* Adjust ip */

	movl	0x4(%ebp), %edx			/* Load parent ip (2nd parameter) */
@@ -93,10 +92,14 @@ GLOBAL(ftrace_regs_call) 
	call	ftrace_stub



	addl	$4, %esp			/* Skip pt_regs */

	movl	14*4(%esp), %eax		/* Move flags back into cs */

	movl	%eax, 13*4(%esp)		/* Needed to keep addl	from modifying flags */

	movl	12*4(%esp), %eax		/* Get return ip from regs->ip */

	movl	%eax, 14*4(%esp)		/* Put return ip back for ret */



	/* restore flags */

	push	14*4(%esp)

	popf



	/* Move return ip back to its original location */

	movl	12*4(%esp), %eax

	movl	%eax, 14*4(%esp)



	popl	%ebx

	popl	%ecx
@@ -109,12 +112,11 @@ GLOBAL(ftrace_regs_call) 
	popl	%es

	popl	%fs

	popl	%gs

	addl	$8, %esp			/* Skip orig_ax and ip */

	popf					/* Pop flags at end (no addl to corrupt flags) */

	jmp	.Lftrace_ret



	popf

	jmp	ftrace_stub

	/* use lea to not affect flags */

	lea	3*4(%esp), %esp			/* Skip orig_ax, ip and cs */



	jmp	.Lftrace_ret

#else /* ! CONFIG_DYNAMIC_FTRACE */



ENTRY(mcount)