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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: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Heiko Carstens 2014-10-08 10:03:08 +02:00 committed by Martin Schwidefsky
parent 53255c9a4d
commit 0cccdda8d1
2 changed files with 10 additions and 15 deletions
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22
arch/s390/kernel/ftrace.c
View File

@ -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 */

3
arch/s390/kernel/mcount.S
View File

@ -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)