[PATCH v3 56/59] x86/ftrace: Remove ftrace_epilogue()

Peter Zijlstra
2022-09-15T11:42:39Z

From: Peter Zijlstra <peterz@infradead.org>

Remove the weird jumps to RET and simply use RET.

This then promotes ftrace_stub() to a real function; which becomes
important for kcfi.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/kernel/ftrace_64.S | 21 ++++++---------------
1 file changed, 6 insertions(+), 15 deletions(-)

--- a/arch/x86/kernel/ftrace_64.S
+++ b/arch/x86/kernel/ftrace_64.S
@@ -172,20 +172,14 @@ SYM_INNER_LABEL(ftrace_call, SYM_L_GLOBA
*/
SYM_INNER_LABEL(ftrace_caller_end, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
-
- jmp ftrace_epilogue
+ RET
SYM_FUNC_END(ftrace_caller);
STACK_FRAME_NON_STANDARD_FP(ftrace_caller)

-SYM_FUNC_START(ftrace_epilogue)
-/*
- * This is weak to keep gas from relaxing the jumps.
- */
-SYM_INNER_LABEL_ALIGN(ftrace_stub, SYM_L_WEAK)
+SYM_FUNC_START(ftrace_stub)
UNWIND_HINT_FUNC
- ENDBR
RET
-SYM_FUNC_END(ftrace_epilogue)
+SYM_FUNC_END(ftrace_stub)

SYM_FUNC_START(ftrace_regs_caller)
/* Save the current flags before any operations that can change them */
@@ -262,14 +256,11 @@ SYM_INNER_LABEL(ftrace_regs_caller_jmp,
popfq

/*
- * As this jmp to ftrace_epilogue can be a short jump
- * it must not be copied into the trampoline.
- * The trampoline will add the code to jump
- * to the return.
+ * The trampoline will add the return.
*/
SYM_INNER_LABEL(ftrace_regs_caller_end, SYM_L_GLOBAL)
ANNOTATE_NOENDBR
- jmp ftrace_epilogue
+ RET

/* Swap the flags with orig_rax */
1: movq MCOUNT_REG_SIZE(%rsp), %rdi
@@ -280,7 +271,7 @@ SYM_INNER_LABEL(ftrace_regs_caller_end,
/* Restore flags */
popfq
UNWIND_HINT_FUNC
- jmp ftrace_epilogue
+ RET

SYM_FUNC_END(ftrace_regs_caller)
STACK_FRAME_NON_STANDARD_FP(ftrace_regs_caller)