linux-kernel - [PATCH v7 2/3] ftrace: introduce FTRACE_IP

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Date:   Wed, 25 Dec 2019 09:42:52 +0000
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jonathan Corbet <corbet@....net>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: [PATCH v7 2/3] ftrace: introduce FTRACE_IP_EXTENSION

On some architectures, the DYNAMIC_FTRACE_WITH_REGS is implemented by
gcc's -fpatchable-function-entry option. Take arm64 for example, arm64
makes use of GCC -fpatchable-function-entry=2 option to insert two
nops. When the function is traced, the first nop will be modified to
the LR saver, then the second nop to "bl <ftrace-entry>". we need to
update ftrace_location() to recognise these two instructions  as being
part of ftrace. To do this, we introduce FTRACE_IP_EXTENSION to let
ftrace_location search IP, IP + FTRACE_IP_EXTENSION range.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
Suggested-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
---
 include/linux/ftrace.h | 4 ++++
 kernel/trace/ftrace.c  | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 7247d35c3d16..05a03b2a2f39 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -20,6 +20,10 @@
 
 #include <asm/ftrace.h>
 
+#ifndef FTRACE_IP_EXTENSION
+#define  FTRACE_IP_EXTENSION 0
+#endif
+
 /*
  * If the arch supports passing the variable contents of
  * function_trace_op as the third parameter back from the
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 74439ab5c2b6..a8cfea502369 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1590,7 +1590,7 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end)
  */
 unsigned long ftrace_location(unsigned long ip)
 {
-	return ftrace_location_range(ip, ip);
+	return ftrace_location_range(ip, ip + FTRACE_IP_EXTENSION);
 }
 
 /**
-- 
2.24.1