x86/ftrace: Make non direct case the default in ftrace_regs_caller

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.

Link: http://lkml.kernel.org/r/20200422162750.350373278@goodmis.org
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

diff --git a/arch/x86/kernel/ftrace_64.S b/arch/x86/kernel/ftrace_64.S
index 083a3da..3ba32cc 100644 (file)
--- 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)