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>
diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c
index f007212..51d14fe5 100644
--- a/arch/s390/kernel/ftrace.c
+++ b/arch/s390/kernel/ftrace.c
@@ -138,28 +138,24 @@
/*
* 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 */
diff --git a/arch/s390/kernel/mcount.S b/arch/s390/kernel/mcount.S
index 07abe8d..4300ea3 100644
--- a/arch/s390/kernel/mcount.S
+++ b/arch/s390/kernel/mcount.S
@@ -49,8 +49,7 @@
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)
