linux-kernel - [PATCH 2/7] arm: ftrace: Add call modify mechanism

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Message-Id: <1481043967-15602-3-git-send-email-abelvesa@linux.com>
Date:   Tue,  6 Dec 2016 17:06:02 +0000
From:   Abel Vesa <abelvesa@...ux.com>
To:     linux@...linux.org.uk, jpoimboe@...hat.com, jeyu@...hat.com,
        jikos@...nel.org, mbenes@...e.cz, pmladek@...e.com
Cc:     rostedt@...dmis.org, mingo@...hat.com, gregkh@...uxfoundation.org,
        geert+renesas@...der.be, davem@...emloft.net,
        akpm@...ux-foundation.org, emil.l.velikov@...il.com,
        mchehab@...nel.org, linux@...ck-us.net, ard.biesheuvel@...aro.org,
        jens.wiklander@...aro.org, jean-philippe.brucker@....com,
        viro@...iv.linux.org.uk, stefano.stabellini@...citrix.com,
        chris.brandt@...esas.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, Abel Vesa <abelvesa@...ux.com>
Subject: [PATCH 2/7] arm: ftrace: Add call modify mechanism

Function ftrace_modify_call provides a way to replace ftrace_stub
with the ftrace function. This helps the klp_ftrace_handler to be
called via ftrace_ops_no_ops, which in turn will set the pc with
the patched function's starting address. This is used for
livepatching.

Signed-off-by: Abel Vesa <abelvesa@...ux.com>
---
 arch/arm/kernel/ftrace.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/arch/arm/kernel/ftrace.c b/arch/arm/kernel/ftrace.c
index 3f17594..cb4543a 100644
--- a/arch/arm/kernel/ftrace.c
+++ b/arch/arm/kernel/ftrace.c
@@ -139,6 +139,15 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 
 	ret = ftrace_modify_code(pc, 0, new, false);
 
+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
+	if (!ret) {
+		pc = (unsigned long)&ftrace_regs_call;
+		new = ftrace_call_replace(pc, (unsigned long)func);
+
+		ret = ftrace_modify_code(pc, 0, new, false);
+	}
+#endif
+
 #ifdef CONFIG_OLD_MCOUNT
 	if (!ret) {
 		pc = (unsigned long)&ftrace_call_old;
@@ -151,6 +160,18 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
 	return ret;
 }
 
+int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
+	       unsigned long addr)
+{
+	unsigned long pc = rec->ip;
+	u32 old, new;
+
+	old = arm_gen_branch(pc, old_addr);
+	new = arm_gen_branch(pc, addr);
+
+	return ftrace_modify_code(pc, old, new, true);
+}
+
 int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 {
 	unsigned long new, old;
-- 
2.7.4