Commit 2481a87b authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky
Browse files

s390/ftrace: optimize function graph caller code 



When the function graph tracer is disabled we can skip three additional
instructions. So let's just do this.

So if function tracing is enabled but function graph tracing is
runtime disabled, we get away with a single unconditional branch.

Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 0f1b1ff5

arch/s390/include/asm/ftrace.h

+1 −0
Original line number Diff line number Diff line
@@ -4,6 +4,7 @@ 
#ifndef __ASSEMBLY__



extern void _mcount(void);

extern char ftrace_graph_caller_end;



struct dyn_arch_ftrace { };

arch/s390/kernel/ftrace.c

+24 −0
Original line number Diff line number Diff line
@@ -170,6 +170,29 @@ out: 
 * directly after the instructions. To enable the call we calculate

 * the original offset to prepare_ftrace_return and put it back.

 */



#ifdef CONFIG_64BIT



int ftrace_enable_ftrace_graph_caller(void)

{

	static unsigned short offset = 0x0002;



	return probe_kernel_write((void *) ftrace_graph_caller + 2,

				  &offset, sizeof(offset));

}



int ftrace_disable_ftrace_graph_caller(void)

{

	unsigned short offset;



	offset = ((void *) &ftrace_graph_caller_end -

		  (void *) ftrace_graph_caller) / 2;

	return probe_kernel_write((void *) ftrace_graph_caller + 2,

				  &offset, sizeof(offset));

}



#else /* CONFIG_64BIT */



int ftrace_enable_ftrace_graph_caller(void)

{

	unsigned short offset;
@@ -188,5 +211,6 @@ int ftrace_disable_ftrace_graph_caller(void) 
				  &offset, sizeof(offset));

}



#endif /* CONFIG_64BIT */

#endif /* CONFIG_DYNAMIC_FTRACE */

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

arch/s390/kernel/mcount64.S

+9 −6
Original line number Diff line number Diff line
@@ -32,14 +32,17 @@ ENTRY(ftrace_caller) 
	lg	%r14,0(%r14)

	basr	%r14,%r14

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

# The j instruction gets runtime patched to a nop instruction.

# See ftrace_enable_ftrace_graph_caller. The patched instruction is:

#	j	.+4

ENTRY(ftrace_graph_caller)

	j	ftrace_graph_caller_end

	lg	%r2,168(%r15)

	lg	%r3,272(%r15)

ENTRY(ftrace_graph_caller)

# The bras instruction gets runtime patched to call prepare_ftrace_return.

# See ftrace_enable_ftrace_graph_caller. The patched instruction is:

#	bras	%r14,prepare_ftrace_return

	bras	%r14,0f

0:	stg	%r2,168(%r15)

	brasl	%r14,prepare_ftrace_return

	stg	%r2,168(%r15)

ftrace_graph_caller_end:

	.globl	ftrace_graph_caller_end

#endif

	aghi	%r15,160

	lmg	%r2,%r5,32(%r15)

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