[PATCH 1/3] x86/ftrace: Make non direct case the default in ftrace_regs_caller

Steven Rostedt
2020-04-22T16:28:02Z

If a direct function is hooked along with one of the ftrace registered
functions, then the ftrace_regs_caller is attached to the function that
shares the direct hook as well as the ftrace hook. The ftrace_regs_caller
will call ftrace_ops_list_func() that iterates through all the registered
ftrace callbacks, and if there's a direct callback attached to that
function, the direct ftrace_ops callback is called to notify that
ftrace_regs_caller to return to the direct caller instead of going back to
the function that called it.

But this is a very uncommon case. Currently, the code has it as the default
case. Modify ftrace_regs_caller to make the default case (the non jump) to
just return normally, and have the jump to the handling of the direct
caller.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
arch/x86/kernel/ftrace_64.S | 31 +++++++++++++++----------------
1 file changed, 15 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 9738ed23964e..c93ee7195af0 100644
--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -241,22 +241,9 @@ SYM_INNER_LABEL(ftrace_regs_call, SYM_L_GLOBAL)
*/
movq ORIG_RAX(%rsp), %rax
testq %rax, %rax
- jz 1f
+ jnz 1f

- /* Swap the flags with orig_rax */
- movq MCOUNT_REG_SIZE(%rsp), %rdi
- movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
- movq %rax, MCOUNT_REG_SIZE(%rsp)
-
- restore_mcount_regs 8
- /* Restore flags */
- popfq
-
-SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL);
- UNWIND_HINT_RET_OFFSET
- jmp ftrace_epilogue
-
-1: restore_mcount_regs
+ restore_mcount_regs
/* Restore flags */
popfq

@@ -266,9 +253,21 @@ SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL);
* The trampoline will add the code to jump
* to the return.
*/
-SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
+SYM_INNER_LABEL(ftrace_regs_caller_ret, SYM_L_GLOBAL)
jmp ftrace_epilogue

+ /* Swap the flags with orig_rax */
+1: movq MCOUNT_REG_SIZE(%rsp), %rdi
+ movq %rdi, MCOUNT_REG_SIZE-8(%rsp)
+ movq %rax, MCOUNT_REG_SIZE(%rsp)
+
+ restore_mcount_regs 8
+ /* Restore flags */
+ popfq
+SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
+ UNWIND_HINT_RET_OFFSET
+ jmp ftrace_epilogue
+
SYM_FUNC_END(ftrace_regs_caller)

--
2.26.1