powerpc: ftrace, use create_branch

Impact: clean up

Paul Mackerras pointed out that the code to determine if the branch
can reach the destination is incorrect. Michael Ellerman suggested
to pull out the code from create_branch and use that.

Simply using create_branch is probably the best.

Reported-by: Michael Ellerman <michael@ellerman.id.au>
Reported-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 12 insertions, 42 deletions

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index a4640e4f1172..5355244c99ff 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -114,19 +114,9 @@ ftrace_modify_code(unsigned long ip, unsigned char *old_code,
  */
 static int test_24bit_addr(unsigned long ip, unsigned long addr)
 {
-        long diff;
 
-        /*
-         * Can we get to addr from ip in 24 bits?
-         *  (26 really, since we mulitply by 4 for 4 byte alignment)
-         */
-        diff = addr - ip;
-
-        /*
-         * Return true if diff is less than 1 << 25
-         *  and greater than -1 << 26.
-         */
-        return (diff < (1 << 25)) && (diff > (-1 << 26));
+        /* use the create_branch to verify that this offset can be branched */
+        return create_branch((unsigned int *)ip, addr, 0);
 }
 
 static int is_bl_op(unsigned int op)
@@ -134,11 +124,6 @@ static int is_bl_op(unsigned int op)
         return (op & 0xfc000003) == 0x48000001;
 }
 
-static int test_offset(unsigned long offset)
-{
-        return (offset + 0x2000000 > 0x3ffffff) || ((offset & 3) != 0);
-}
-
 static unsigned long find_bl_target(unsigned long ip, unsigned int op)
 {
         static int offset;
@@ -151,12 +136,6 @@ static unsigned long find_bl_target(unsigned long ip, unsigned int op)
         return ip + (long)offset;
 }
 
-static unsigned int branch_offset(unsigned long offset)
-{
-        /* return "bl ip+offset" */
-        return 0x48000001 | (offset & 0x03fffffc);
-}
-
 #ifdef CONFIG_PPC64
 static int
 __ftrace_make_nop(struct module *mod,
@@ -402,7 +381,6 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
         unsigned int op[2];
         unsigned long ip = rec->ip;
-        unsigned long offset;
 
         /* read where this goes */
         if (probe_kernel_read(op, (void *)ip, MCOUNT_INSN_SIZE * 2))
@@ -424,17 +402,14 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
                 return -EINVAL;
         }
 
-        /* now calculate a jump to the ftrace caller trampoline */
-        offset = rec->arch.mod->arch.tramp - ip;
-
-        if (test_offset(offset)) {
-                printk(KERN_ERR "REL24 %li out of range!\n",
-                       (long int)offset);
+        /* create the branch to the trampoline */
+        op[0] = create_branch((unsigned int *)ip,
+                              rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
+        if (!op[0]) {
+                printk(KERN_ERR "REL24 out of range!\n");
                 return -EINVAL;
         }
 
-        /* Set to "bl addr" */
-        op[0] = branch_offset(offset);
         /* ld r2,40(r1) */
         op[1] = 0xe8410028;
 
@@ -453,7 +428,6 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
         unsigned int op;
         unsigned long ip = rec->ip;
-        unsigned long offset;
 
         /* read where this goes */
         if (probe_kernel_read(&op, (void *)ip, MCOUNT_INSN_SIZE))
@@ -471,18 +445,14 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
                 return -EINVAL;
         }
 
-        /* now calculate a jump to the ftrace caller trampoline */
-        offset = rec->arch.mod->arch.tramp - ip;
-
-        if (test_offset(offset)) {
-                printk(KERN_ERR "REL24 %li out of range!\n",
-                       (long int)offset);
+        /* create the branch to the trampoline */
+        op = create_branch((unsigned int *)ip,
+                           rec->arch.mod->arch.tramp, BRANCH_SET_LINK);
+        if (!op) {
+                printk(KERN_ERR "REL24 out of range!\n");
                 return -EINVAL;
         }
 
-        /* Set to "bl addr" */
-        op = branch_offset(offset);
-
         DEBUGP("write to %lx\n", rec->ip);
 
         if (probe_kernel_write((void *)ip, &op, MCOUNT_INSN_SIZE))