ftrace/x86: Add separate function to save regs

Add a way to have different functions calling different trampolines.
If a ftrace_ops wants regs saved on the return, then have only the
functions with ops registered to save regs. Functions registered by
other ops would not be affected, unless the functions overlap.

If one ftrace_ops registered functions A, B and C and another ops
registered fucntions to save regs on A, and D, then only functions
A and D would be saving regs. Function B and C would work as normal.
Although A is registered by both ops: normal and saves regs; this is fine
as saving the regs is needed to satisfy one of the ops that calls it
but the regs are ignored by the other ops function.

x86_64 implements the full regs saving, and i386 just passes a NULL
for regs to satisfy the ftrace_ops passing. Where an arch must supply
both regs and ftrace_ops parameters, even if regs is just NULL.

It is OK for an arch to pass NULL regs. All function trace users that
require regs passing must add the flag FTRACE_OPS_FL_SAVE_REGS when
registering the ftrace_ops. If the arch does not support saving regs
then the ftrace_ops will fail to register. The flag
FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED may be set that will prevent the
ftrace_ops from failing to register. In this case, the handler may
either check if regs is not NULL or check if ARCH_SUPPORTS_FTRACE_SAVE_REGS.
If the arch supports passing regs it will set this macro and pass regs
for ops that request them. All other archs will just pass NULL.

Link: Link: http://lkml.kernel.org/r/20120711195745.107705970@goodmis.org

Cc: Alexander van Heukelum <heukelum@fastmail.fm>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

1 files changed, 83 insertions, 8 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 6ff07ad0ede3..c55f7e274613 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -314,6 +314,20 @@ static int __register_ftrace_function(struct ftrace_ops *ops)
         if ((ops->flags & FL_GLOBAL_CONTROL_MASK) == FL_GLOBAL_CONTROL_MASK)
                 return -EINVAL;
 
+#ifndef ARCH_SUPPORTS_FTRACE_SAVE_REGS
+        /*
+         * If the ftrace_ops specifies SAVE_REGS, then it only can be used
+         * if the arch supports it, or SAVE_REGS_IF_SUPPORTED is also set.
+         * Setting SAVE_REGS_IF_SUPPORTED makes SAVE_REGS irrelevant.
+         */
+        if (ops->flags & FTRACE_OPS_FL_SAVE_REGS &&
+            !(ops->flags & FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED))
+                return -EINVAL;
+
+        if (ops->flags & FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED)
+                ops->flags |= FTRACE_OPS_FL_SAVE_REGS;
+#endif
+
         if (!core_kernel_data((unsigned long)ops))
                 ops->flags |= FTRACE_OPS_FL_DYNAMIC;
 
@@ -1515,6 +1529,12 @@ static void __ftrace_hash_rec_update(struct ftrace_ops *ops,
                         rec->flags++;
                         if (FTRACE_WARN_ON((rec->flags & ~FTRACE_FL_MASK) == FTRACE_REF_MAX))
                                 return;
+                        /*
+                         * If any ops wants regs saved for this function
+                         * then all ops will get saved regs.
+                         */
+                        if (ops->flags & FTRACE_OPS_FL_SAVE_REGS)
+                                rec->flags |= FTRACE_FL_REGS;
                 } else {
                         if (FTRACE_WARN_ON((rec->flags & ~FTRACE_FL_MASK) == 0))
                                 return;
@@ -1606,18 +1626,59 @@ static int ftrace_check_record(struct dyn_ftrace *rec, int enable, int update)
         if (enable && (rec->flags & ~FTRACE_FL_MASK))
                 flag = FTRACE_FL_ENABLED;
 
+        /*
+         * If enabling and the REGS flag does not match the REGS_EN, then
+         * do not ignore this record. Set flags to fail the compare against
+         * ENABLED.
+         */
+        if (flag &&
+            (!(rec->flags & FTRACE_FL_REGS) != !(rec->flags & FTRACE_FL_REGS_EN)))
+                flag |= FTRACE_FL_REGS;
+
         /* If the state of this record hasn't changed, then do nothing */
         if ((rec->flags & FTRACE_FL_ENABLED) == flag)
                 return FTRACE_UPDATE_IGNORE;
 
         if (flag) {
-                if (update)
+                /* Save off if rec is being enabled (for return value) */
+                flag ^= rec->flags & FTRACE_FL_ENABLED;
+
+                if (update) {
                         rec->flags |= FTRACE_FL_ENABLED;
-                return FTRACE_UPDATE_MAKE_CALL;
+                        if (flag & FTRACE_FL_REGS) {
+                                if (rec->flags & FTRACE_FL_REGS)
+                                        rec->flags |= FTRACE_FL_REGS_EN;
+                                else
+                                        rec->flags &= ~FTRACE_FL_REGS_EN;
+                        }
+                }
+
+                /*
+                 * If this record is being updated from a nop, then
+                 *   return UPDATE_MAKE_CALL.
+                 * Otherwise, if the EN flag is set, then return
+                 *   UPDATE_MODIFY_CALL_REGS to tell the caller to convert
+                 *   from the non-save regs, to a save regs function.
+                 * Otherwise,
+                 *   return UPDATE_MODIFY_CALL to tell the caller to convert
+                 *   from the save regs, to a non-save regs function.
+                 */
+                if (flag & FTRACE_FL_ENABLED)
+                        return FTRACE_UPDATE_MAKE_CALL;
+                else if (rec->flags & FTRACE_FL_REGS_EN)
+                        return FTRACE_UPDATE_MODIFY_CALL_REGS;
+                else
+                        return FTRACE_UPDATE_MODIFY_CALL;
         }
 
-        if (update)
-                rec->flags &= ~FTRACE_FL_ENABLED;
+        if (update) {
+                /* If there's no more users, clear all flags */
+                if (!(rec->flags & ~FTRACE_FL_MASK))
+                        rec->flags = 0;
+                else
+                        /* Just disable the record (keep REGS state) */
+                        rec->flags &= ~FTRACE_FL_ENABLED;
+        }
 
         return FTRACE_UPDATE_MAKE_NOP;
 }
@@ -1652,13 +1713,17 @@ int ftrace_test_record(struct dyn_ftrace *rec, int enable)
 static int
 __ftrace_replace_code(struct dyn_ftrace *rec, int enable)
 {
+        unsigned long ftrace_old_addr;
         unsigned long ftrace_addr;
         int ret;
 
-        ftrace_addr = (unsigned long)FTRACE_ADDR;
-
         ret = ftrace_update_record(rec, enable);
 
+        if (rec->flags & FTRACE_FL_REGS)
+                ftrace_addr = (unsigned long)FTRACE_REGS_ADDR;
+        else
+                ftrace_addr = (unsigned long)FTRACE_ADDR;
+
         switch (ret) {
         case FTRACE_UPDATE_IGNORE:
                 return 0;
@@ -1668,6 +1733,15 @@ __ftrace_replace_code(struct dyn_ftrace *rec, int enable)
 
         case FTRACE_UPDATE_MAKE_NOP:
                 return ftrace_make_nop(NULL, rec, ftrace_addr);
+
+        case FTRACE_UPDATE_MODIFY_CALL_REGS:
+        case FTRACE_UPDATE_MODIFY_CALL:
+                if (rec->flags & FTRACE_FL_REGS)
+                        ftrace_old_addr = (unsigned long)FTRACE_ADDR;
+                else
+                        ftrace_old_addr = (unsigned long)FTRACE_REGS_ADDR;
+
+                return ftrace_modify_call(rec, ftrace_old_addr, ftrace_addr);
         }
 
         return -1; /* unknow ftrace bug */
@@ -2421,8 +2495,9 @@ static int t_show(struct seq_file *m, void *v)
 
         seq_printf(m, "%ps", (void *)rec->ip);
         if (iter->flags & FTRACE_ITER_ENABLED)
-                seq_printf(m, " (%ld)",
-                           rec->flags & ~FTRACE_FL_MASK);
+                seq_printf(m, " (%ld)%s",
+                           rec->flags & ~FTRACE_FL_MASK,
+                           rec->flags & FTRACE_FL_REGS ? " R" : "");
         seq_printf(m, "\n");
 
         return 0;