powerpc/ftrace: simplify prepare_ftrace_return
Instead of passing in the stack address of the link register
to be modified, just pass in the old value and return the
new value and rely on ftrace_graph_caller to do the
modification.
This removes the exception handling around the stack update -
it isn't needed and we weren't consistent about it. Later on
we would do an unprotected modification:
if (!ftrace_graph_entry(&trace)) {
*parent = old;
Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/kernel/entry_32.S b/arch/powerpc/kernel/entry_32.S
index 22b45a4..ad837d8 100644
--- a/arch/powerpc/kernel/entry_32.S
+++ b/arch/powerpc/kernel/entry_32.S
@@ -1424,12 +1424,18 @@
lwz r4, 44(r1)
subi r4, r4, MCOUNT_INSN_SIZE
- /* get the parent address */
- addi r3, r1, 52
+ /* Grab the LR out of the caller stack frame */
+ lwz r3,52(r1)
bl prepare_ftrace_return
nop
+ /*
+ * prepare_ftrace_return gives us the address we divert to.
+ * Change the LR in the callers stack frame to this.
+ */
+ stw r3,52(r1)
+
MCOUNT_RESTORE_FRAME
/* old link register ends up in ctr reg */
bctr
diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
index 66f7ed3..194e46d 100644
--- a/arch/powerpc/kernel/entry_64.S
+++ b/arch/powerpc/kernel/entry_64.S
@@ -1227,13 +1227,20 @@
ld r4, 128(r1)
subi r4, r4, MCOUNT_INSN_SIZE
- /* get the parent address */
+ /* Grab the LR out of the caller stack frame */
ld r11, 112(r1)
- addi r3, r11, 16
+ ld r3, 16(r11)
bl prepare_ftrace_return
nop
+ /*
+ * prepare_ftrace_return gives us the address we divert to.
+ * Change the LR in the callers stack frame to this.
+ */
+ ld r11, 112(r1)
+ std r3, 16(r11)
+
ld r0, 128(r1)
mtlr r0
addi r1, r1, 112
diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index abf7921..d795031 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -512,67 +512,34 @@
/*
* Hook the return address and push it in the stack of return addrs
- * in current thread info.
+ * in current thread info. Return the address we want to divert to.
*/
-void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr)
+unsigned long prepare_ftrace_return(unsigned long parent, unsigned long ip)
{
- unsigned long old;
- int faulted;
struct ftrace_graph_ent trace;
unsigned long return_hooker;
if (unlikely(ftrace_graph_is_dead()))
- return;
+ goto out;
if (unlikely(atomic_read(¤t->tracing_graph_pause)))
- return;
+ goto out;
return_hooker = ppc_function_entry(return_to_handler);
- /*
- * Protect against fault, even if it shouldn't
- * happen. This tool is too much intrusive to
- * ignore such a protection.
- */
- asm volatile(
- "1: " PPC_LL "%[old], 0(%[parent])\n"
- "2: " PPC_STL "%[return_hooker], 0(%[parent])\n"
- " li %[faulted], 0\n"
- "3:\n"
-
- ".section .fixup, \"ax\"\n"
- "4: li %[faulted], 1\n"
- " b 3b\n"
- ".previous\n"
-
- ".section __ex_table,\"a\"\n"
- PPC_LONG_ALIGN "\n"
- PPC_LONG "1b,4b\n"
- PPC_LONG "2b,4b\n"
- ".previous"
-
- : [old] "=&r" (old), [faulted] "=r" (faulted)
- : [parent] "r" (parent), [return_hooker] "r" (return_hooker)
- : "memory"
- );
-
- if (unlikely(faulted)) {
- ftrace_graph_stop();
- WARN_ON(1);
- return;
- }
-
- trace.func = self_addr;
+ trace.func = ip;
trace.depth = current->curr_ret_stack + 1;
/* Only trace if the calling function expects to */
- if (!ftrace_graph_entry(&trace)) {
- *parent = old;
- return;
- }
+ if (!ftrace_graph_entry(&trace))
+ goto out;
- if (ftrace_push_return_trace(old, self_addr, &trace.depth, 0) == -EBUSY)
- *parent = old;
+ if (ftrace_push_return_trace(parent, ip, &trace.depth, 0) == -EBUSY)
+ goto out;
+
+ parent = return_hooker;
+out:
+ return parent;
}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */