From 0cccdda8d1512af4d3f6913044e8c8e58e15ef37 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Wed, 8 Oct 2014 10:03:08 +0200 Subject: 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 Signed-off-by: Martin Schwidefsky --- arch/s390/kernel/ftrace.c | 22 +++++++++------------- arch/s390/kernel/mcount.S | 3 +-- 2 files changed, 10 insertions(+), 15 deletions(-) (limited to 'arch/s390') diff --git a/arch/s390/kernel/ftrace.c b/arch/s390/kernel/ftrace.c index f0072125926c..51d14fe5eb9a 100644 --- a/arch/s390/kernel/ftrace.c +++ b/arch/s390/kernel/ftrace.c @@ -138,28 +138,24 @@ out: /* * 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 07abe8d464d4..4300ea374826 100644 --- a/arch/s390/kernel/mcount.S +++ b/arch/s390/kernel/mcount.S @@ -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) -- cgit v1.2.3-55-g7522