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Commit b3c18725 authored by Anton Blanchard's avatar Anton Blanchard Committed by Michael Ellerman
Browse files

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: default avatarAnton Blanchard <anton@samba.org>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent 7d56c65a

arch/powerpc/kernel/entry_32.S

+8 −2
Original line number Diff line number Diff line
@@ -1424,12 +1424,18 @@ _GLOBAL(ftrace_graph_caller) 
	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

arch/powerpc/kernel/entry_64.S

+9 −2
Original line number Diff line number Diff line
@@ -1227,13 +1227,20 @@ _GLOBAL(ftrace_graph_caller) 
	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

arch/powerpc/kernel/ftrace.c

+13 −46
Original line number Diff line number Diff line
@@ -512,67 +512,34 @@ int ftrace_disable_ftrace_graph_caller(void) 


/*

 * 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(&current->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(parent, ip, &trace.depth, 0) == -EBUSY)

		goto out;



	if (ftrace_push_return_trace(old, self_addr, &trace.depth, 0) == -EBUSY)

		*parent = old;

	parent = return_hooker;

out:

	return parent;

}

#endif /* CONFIG_FUNCTION_GRAPH_TRACER */