1 files changed, 61 insertions, 7 deletions

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 96aadbfedcc6..4151c91254e8 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -16,8 +16,8 @@
 #include <linux/init.h>
 #include <linux/list.h>
 
-#include <asm/alternative.h>
 #include <asm/ftrace.h>
+#include <asm/nops.h>
 
 
 /* Long is fine, even if it is only 4 bytes ;-) */
@@ -119,13 +119,67 @@ notrace int ftrace_mcount_set(unsigned long *data)
 
 int __init ftrace_dyn_arch_init(void *data)
 {
-        const unsigned char *const *noptable = find_nop_table();
-
-        /* This is running in kstop_machine */
-
-        ftrace_mcount_set(data);
+        extern const unsigned char ftrace_test_p6nop[];
+        extern const unsigned char ftrace_test_nop5[];
+        extern const unsigned char ftrace_test_jmp[];
+        int faulted = 0;
 
-        ftrace_nop = (unsigned long *)noptable[MCOUNT_INSN_SIZE];
+        /*
+         * 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 (
+                "jmp ftrace_test_jmp\n"
+                /* This code needs to stay around */
+                ".section .text, \"ax\"\n"
+                "ftrace_test_jmp:"
+                "jmp ftrace_test_p6nop\n"
+                ".byte 0x00,0x00,0x00\n"  /* 2 byte jmp + 3 bytes */
+                "ftrace_test_p6nop:"
+                P6_NOP5
+                "jmp 1f\n"
+                "ftrace_test_nop5:"
+                ".byte 0x66,0x66,0x66,0x66,0x90\n"
+                "jmp 1f\n"
+                ".previous\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("ftrace: converting mcount calls to 0f 1f 44 00 00\n");
+                ftrace_nop = (unsigned long *)ftrace_test_p6nop;
+                break;
+        case 1:
+                pr_info("ftrace: converting mcount calls to 66 66 66 66 90\n");
+                ftrace_nop = (unsigned long *)ftrace_test_nop5;
+                break;
+        case 2:
+                pr_info("ftrace: converting mcount calls to jmp 1f\n");
+                ftrace_nop = (unsigned long *)ftrace_test_jmp;
+                break;
+        }
+
+        /* The return code is retured via data */
+        *(unsigned long *)data = 0;
 
         return 0;
 }