jump label: Make dynamic no-op selection available outside of ftrace
Move Steve's code for finding the best 5-byte no-op from ftrace.c to
alternative.c. The idea is that other consumers (in this case jump label)
want to make use of that code.
Signed-off-by: Jason Baron <jbaron@redhat.com>
LKML-Reference: <96259ae74172dcac99c0020c249743c523a92e18.1284733808.git.jbaron@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index f65ab8b..1849d80 100644
--- a/arch/x86/kernel/alternative.c
+++ b/arch/x86/kernel/alternative.c
@@ -641,3 +641,67 @@
return addr;
}
+#if defined(CONFIG_DYNAMIC_FTRACE)
+
+unsigned char ideal_nop5[IDEAL_NOP_SIZE_5];
+
+void __init arch_init_ideal_nop5(void)
+{
+ extern const unsigned char ftrace_test_p6nop[];
+ extern const unsigned char ftrace_test_nop5[];
+ extern const unsigned char ftrace_test_jmp[];
+ int faulted = 0;
+
+ /*
+ * There is no good nop for all x86 archs.
+ * We will default to using the P6_NOP5, but first we
+ * will test to make sure that the nop will actually
+ * work on this CPU. If it faults, we will then
+ * go to a lesser efficient 5 byte nop. If that fails
+ * we then just use a jmp as our nop. This isn't the most
+ * efficient nop, but we can not use a multi part nop
+ * since we would then risk being preempted in the middle
+ * of that nop, and if we enabled tracing then, it might
+ * cause a system crash.
+ *
+ * TODO: check the cpuid to determine the best nop.
+ */
+ asm volatile (
+ "ftrace_test_jmp:"
+ "jmp ftrace_test_p6nop\n"
+ "nop\n"
+ "nop\n"
+ "nop\n" /* 2 byte jmp + 3 bytes */
+ "ftrace_test_p6nop:"
+ P6_NOP5
+ "jmp 1f\n"
+ "ftrace_test_nop5:"
+ ".byte 0x66,0x66,0x66,0x66,0x90\n"
+ "1:"
+ ".section .fixup, \"ax\"\n"
+ "2: movl $1, %0\n"
+ " jmp ftrace_test_nop5\n"
+ "3: movl $2, %0\n"
+ " jmp 1b\n"
+ ".previous\n"
+ _ASM_EXTABLE(ftrace_test_p6nop, 2b)
+ _ASM_EXTABLE(ftrace_test_nop5, 3b)
+ : "=r"(faulted) : "0" (faulted));
+
+ switch (faulted) {
+ case 0:
+ pr_info("converting mcount calls to 0f 1f 44 00 00\n");
+ memcpy(ideal_nop5, ftrace_test_p6nop, IDEAL_NOP_SIZE_5);
+ break;
+ case 1:
+ pr_info("converting mcount calls to 66 66 66 66 90\n");
+ memcpy(ideal_nop5, ftrace_test_nop5, IDEAL_NOP_SIZE_5);
+ break;
+ case 2:
+ pr_info("converting mcount calls to jmp . + 5\n");
+ memcpy(ideal_nop5, ftrace_test_jmp, IDEAL_NOP_SIZE_5);
+ break;
+ }
+
+}
+#endif