Commit 654b3fa6 authored Oct 30, 2024 by Naveen N Rao Committed by Michael Ellerman Oct 31, 2024

powerpc32/ftrace: Unify 32-bit and 64-bit ftrace entry code



On 32-bit powerpc, gcc generates a three instruction sequence for
function profiling:
	mflr	r0
	stw	r0, 4(r1)
	bl	_mcount

On kernel boot, the call to _mcount() is nop-ed out, to be patched back
in when ftrace is actually enabled. The 'stw' instruction therefore is
not necessary unless ftrace is enabled. Nop it out during ftrace init.

When ftrace is enabled, we want the 'stw' so that stack unwinding works
properly. Perform the same within the ftrace handler, similar to 64-bit
powerpc.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241030070850.1361304-5-hbathini@linux.ibm.com

parent 161d62c2

arch/powerpc/kernel/trace/ftrace.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -240,8 +240,10 @@ int ftrace_init_nop(struct module mod, struct dyn_ftrace rec)
		} else if (IS_ENABLED(CONFIG_PPC32)) {
		/* Expected sequence: 'mflr r0', 'stw r0,4(r1)', 'bl _mcount' */
		ret = ftrace_validate_inst(ip - 8, ppc_inst(PPC_RAW_MFLR(_R0)));
		if (!ret)
		ret = ftrace_validate_inst(ip - 4, ppc_inst(PPC_RAW_STW(_R0, _R1, 4)));
		if (ret)
		return ret;
		ret = ftrace_modify_code(ip - 4, ppc_inst(PPC_RAW_STW(_R0, _R1, 4)),
		ppc_inst(PPC_RAW_NOP()));
		} else if (IS_ENABLED(CONFIG_MPROFILE_KERNEL)) {
		/* Expected sequence: 'mflr r0', ['std r0,16(r1)'], 'bl _mcount' */
		ret = ftrace_read_inst(ip - 4, &old);

arch/powerpc/kernel/trace/ftrace_entry.S

+2 −2

Original line number	Diff line number	Diff line
		@@ -33,6 +33,8 @@
		* and then arrange for the ftrace function to be called.
		*/
		.macro ftrace_regs_entry allregs
		/* Save the original return address in A's stack frame */
		PPC_STL r0, LRSAVE(r1)
		/* Create a minimal stack frame for representing B */
		PPC_STLU r1, -STACK_FRAME_MIN_SIZE(r1)

		@@ -44,8 +46,6 @@
		SAVE_GPRS(3, 10, r1)

		#ifdef CONFIG_PPC64
		/* Save the original return address in A's stack frame */
		std r0, LRSAVE+SWITCH_FRAME_SIZE+STACK_FRAME_MIN_SIZE(r1)
		/* Ok to continue? */
		lbz r3, PACA_FTRACE_ENABLED(r13)
		cmpdi r3, 0