Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit 0cccdda8 authored by Heiko Carstens's avatar Heiko Carstens Committed by Martin Schwidefsky
Browse files

s390/ftrace: simplify enabling/disabling of ftrace_graph_caller 



We can simply patch the mask field within the branch relative on
condition instruction at the beginning of the ftrace_graph_caller
code block.
This makes the logic even simpler and we get rid of the displacement
calculation.

Signed-off-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 53255c9a

arch/s390/kernel/ftrace.c

+9 −13
Original line number Diff line number Diff line
@@ -138,28 +138,24 @@ unsigned long __kprobes prepare_ftrace_return(unsigned long parent, 


/*

 * Patch the kernel code at ftrace_graph_caller location. The instruction

 * there is branch relative and save to prepare_ftrace_return. To disable

 * the call to prepare_ftrace_return we patch the bras offset to point

 * directly after the instructions. To enable the call we calculate

 * the original offset to prepare_ftrace_return and put it back.

 * there is branch relative on condition. To enable the ftrace graph code

 * block, we simply patch the mask field of the instruction to zero and

 * turn the instruction into a nop.

 * To disable the ftrace graph code the mask field will be patched to

 * all ones, which turns the instruction into an unconditional branch.

 */



int ftrace_enable_ftrace_graph_caller(void)

{

	static unsigned short offset = 0x0002;

	u8 op = 0x04; /* set mask field to zero */



	return probe_kernel_write((void *) ftrace_graph_caller + 2,

				  &offset, sizeof(offset));

	return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));

}



int ftrace_disable_ftrace_graph_caller(void)

{

	unsigned short offset;

	u8 op = 0xf4; /* set mask field to all ones */



	offset = ((void *) &ftrace_graph_caller_end -

		  (void *) ftrace_graph_caller) / 2;

	return probe_kernel_write((void *) ftrace_graph_caller + 2,

				  &offset, sizeof(offset));

	return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));

}



#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

arch/s390/kernel/mcount.S

+1 −2
Original line number Diff line number Diff line
@@ -49,8 +49,7 @@ ENTRY(ftrace_caller) 
	basr	%r14,%r1

#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

# See ftrace_enable_ftrace_graph_caller.

ENTRY(ftrace_graph_caller)

	j	ftrace_graph_caller_end

	lg	%r2,(STACK_PTREGS_GPRS+14*8)(%r15)