linux-kernel - [PATCH v2 08/13] powerpc/ftrace: Prepare PPC64's ftrace_caller() for CONFIG_DYNAMIC_FTRACE_WITH

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Date:   Mon, 20 Dec 2021 16:38:25 +0000
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N . Rao" <naveen.n.rao@...ux.vnet.ibm.com>
CC:     Christophe Leroy <christophe.leroy@...roup.eu>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>
Subject: [PATCH v2 08/13] powerpc/ftrace: Prepare PPC64's ftrace_caller() for
 CONFIG_DYNAMIC_FTRACE_WITH_ARGS

In order to implement CONFIG_DYNAMIC_FTRACE_WITH_ARGS, change ftrace_caller()
to handle LIVEPATCH the same way as frace_caller_regs().

Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
---
 .../powerpc/kernel/trace/ftrace_64_mprofile.S | 25 ++++++++++++++-----
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
index d636fc755f60..f6f787819273 100644
--- a/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
+++ b/arch/powerpc/kernel/trace/ftrace_64_mprofile.S
@@ -172,14 +172,19 @@ _GLOBAL(ftrace_caller)
 	addi	r3, r3, function_trace_op@toc@l
 	ld	r5, 0(r3)
 
+#ifdef CONFIG_LIVEPATCH_64
+	SAVE_GPR(14, r1)
+	mr	r14,r7		/* remember old NIP */
+#endif
 	/* Calculate ip from nip-4 into r3 for call below */
 	subi    r3, r7, MCOUNT_INSN_SIZE
 
 	/* Put the original return address in r4 as parent_ip */
+	std	r0, _LINK(r1)
 	mr	r4, r0
 
-	/* Set pt_regs to NULL */
-	li	r6, 0
+	/* Load &pt_regs in r6 for call below */
+	addi    r6, r1 ,STACK_FRAME_OVERHEAD
 
 	/* ftrace_call(r3, r4, r5, r6) */
 .globl ftrace_call
@@ -189,6 +194,10 @@ ftrace_call:
 
 	ld	r3, _NIP(r1)
 	mtctr	r3
+#ifdef CONFIG_LIVEPATCH_64
+	cmpd	r14, r3		/* has NIP been altered? */
+	REST_GPR(14, r1)
+#endif
 
 	/* Restore gprs */
 	REST_GPRS(3, 10, r1)
@@ -196,13 +205,17 @@ ftrace_call:
 	/* Restore callee's TOC */
 	ld	r2, 24(r1)
 
+	/* Restore possibly modified LR */
+	ld	r0, _LINK(r1)
+	mtlr	r0
+
 	/* Pop our stack frame */
 	addi	r1, r1, SWITCH_FRAME_SIZE
 
-	/* Reload original LR */
-	ld	r0, LRSAVE(r1)
-	mtlr	r0
-
+#ifdef CONFIG_LIVEPATCH_64
+        /* Based on the cmpd above, if the NIP was altered handle livepatch */
+	bne-	livepatch_handler
+#endif
 	/* Handle function_graph or go back */
 	b	ftrace_caller_common
 
-- 
2.33.1