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: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 9 insertions, 6 deletions

diff --git a/arch/s390/kernel/mcount64.S b/arch/s390/kernel/mcount64.S
index c67a8bf0fd9a..5b33c83adde9 100644
--- a/arch/s390/kernel/mcount64.S
+++ b/arch/s390/kernel/mcount64.S
@@ -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)