x86/ftrace: Fix warning and considate ftrace_jmp_replace() and ftrace_call_replace()

Arnd reported the following compiler warning:

arch/x86/kernel/ftrace.c:669:23: error: 'ftrace_jmp_replace' defined but not used [-Werror=unused-function]

The ftrace_jmp_replace() function now only has a single user and should be
simply moved by that user. But looking at the code, it shows that
ftrace_jmp_replace() is similar to ftrace_call_replace() except that instead
of using the opcode of 0xe8 it uses 0xe9. It makes more sense to consolidate
that function into one implementation that both ftrace_jmp_replace() and
ftrace_call_replace() use by passing in the op code separate.

The structure in ftrace_code_union is also modified to replace the "e8"
field with the more appropriate name "op".

Cc: stable@vger.kernel.org
Reported-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: http://lkml.kernel.org/r/20190304200748.1418790-1-arnd@arndb.de
Fixes: d2a68c4effd8 ("x86/ftrace: Do not call function graph from dynamic trampolines")
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 8257a59..763d426 100644 (file)
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -49,7 +49,7 @@ int ftrace_arch_code_modify_post_process(void)
 union ftrace_code_union {
        char code[MCOUNT_INSN_SIZE];
        struct {
-               unsigned char e8;
+               unsigned char op;
                int offset;
        } __attribute__((packed));
 };
@@ -59,20 +59,23 @@ static int ftrace_calc_offset(long ip, long addr)
        return (int)(addr - ip);
 }
 
-static unsigned char *ftrace_call_replace(unsigned long ip, unsigned long addr)
+static unsigned char *
+ftrace_text_replace(unsigned char op, unsigned long ip, unsigned long addr)
 {
        static union ftrace_code_union calc;
 
-       calc.e8         = 0xe8;
+       calc.op         = op;
        calc.offset     = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
 
-       /*
-        * No locking needed, this must be called via kstop_machine
-        * which in essence is like running on a uniprocessor machine.
-        */
        return calc.code;
 }
 
+static unsigned char *
+ftrace_call_replace(unsigned long ip, unsigned long addr)
+{
+       return ftrace_text_replace(0xe8, ip, addr);
+}
+
 static inline int
 within(unsigned long addr, unsigned long start, unsigned long end)
 {
@@ -664,22 +667,6 @@ int __init ftrace_dyn_arch_init(void)
        return 0;
 }
 
-#if defined(CONFIG_X86_64) || defined(CONFIG_FUNCTION_GRAPH_TRACER)
-static unsigned char *ftrace_jmp_replace(unsigned long ip, unsigned long addr)
-{
-       static union ftrace_code_union calc;
-
-       /* Jmp not a call (ignore the .e8) */
-       calc.e8         = 0xe9;
-       calc.offset     = ftrace_calc_offset(ip + MCOUNT_INSN_SIZE, addr);
-
-       /*
-        * ftrace external locks synchronize the access to the static variable.
-        */
-       return calc.code;
-}
-#endif
-
 /* Currently only x86_64 supports dynamic trampolines */
 #ifdef CONFIG_X86_64
 
@@ -891,8 +878,8 @@ static void *addr_from_call(void *ptr)
                return NULL;
 
        /* Make sure this is a call */
-       if (WARN_ON_ONCE(calc.e8 != 0xe8)) {
-               pr_warn("Expected e8, got %x\n", calc.e8);
+       if (WARN_ON_ONCE(calc.op != 0xe8)) {
+               pr_warn("Expected e8, got %x\n", calc.op);
                return NULL;
        }
 
@@ -963,6 +950,11 @@ void arch_ftrace_trampoline_free(struct ftrace_ops *ops)
 #ifdef CONFIG_DYNAMIC_FTRACE
 extern void ftrace_graph_call(void);
 
+static unsigned char *ftrace_jmp_replace(unsigned long ip, unsigned long addr)
+{
+       return ftrace_text_replace(0xe9, ip, addr);
+}
+
 static int ftrace_mod_jmp(unsigned long ip, void *func)
 {
        unsigned char *new;