linux-kernel - [RFC PATCH v3 07/26] ftrace: allow search ftrace addr before ftrace fully inited.

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Message-ID: <1423806034-61781-1-git-send-email-wangnan0@huawei.com>
Date:	Fri, 13 Feb 2015 13:40:34 +0800
From:	Wang Nan <wangnan0@...wei.com>
To:	<linux@....linux.org.uk>, <tglx@...utronix.de>, <mingo@...hat.com>,
	<hpa@...or.com>, <rostedt@...dmis.org>, <ananth@...ibm.com>,
	<anil.s.keshavamurthy@...el.com>, <davem@...emloft.net>,
	<masami.hiramatsu.pt@...achi.com>, <luto@...capital.net>,
	<keescook@...omium.org>, <oleg@...hat.com>, <wangnan0@...wei.com>,
	<dave.long@...aro.org>, <tixy@...aro.org>, <nico@...aro.org>,
	<yalin.wang2010@...il.com>, <catalin.marinas@....com>,
	<Yalin.Wang@...ymobile.com>, <mark.rutland@....com>,
	<dave.hansen@...ux.intel.com>, <jkenisto@...ibm.com>,
	<anton@...ba.org>, <stefani@...bold.net>, <JBeulich@...e.com>,
	<akpm@...ux-foundation.org>, <rusty@...tcorp.com.au>,
	<peterz@...radead.org>, <prarit@...hat.com>, <fabf@...net.be>,
	<hannes@...xchg.org>
CC:	<x86@...nel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>, <lizefan@...wei.com>
Subject: [RFC PATCH v3 07/26] ftrace: allow search ftrace addr before ftrace fully inited.

This patch enables ftrace_location() to be used before ftrace_init().
The first user should be early kprobes, which can insert kprobes to
kernel code even before setup_arch() finishes. This patch gives it a
chance to determine whether it is probing ftrace entries and allows it
do some special treatment.

ftrace_cmp_ips_insn() is introduced to make early ftrace_location()
behavior consistent with normal ftrace_location(). With existing
ftrace_cmp_ips(), searching an address in middle of an instruction will
fail, which is inconsistent with ftrace_cmp_recs() used by normal
ftrace_location().

With this and previous patch ftrace_location() now is able to be called
in and after setup_arch().

Signed-off-by: Wang Nan <wangnan0@...wei.com>
---
 kernel/trace/ftrace.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index a75cfbe..fc0c1aa 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1539,6 +1539,8 @@ static unsigned long ftrace_location_range(unsigned long start, unsigned long en
 	return 0;
 }
 
+static unsigned long ftrace_search_mcount_ip(unsigned long ip);
+
 /**
  * ftrace_location - return true if the ip giving is a traced location
  * @ip: the instruction pointer to check
@@ -1550,6 +1552,9 @@ static unsigned long ftrace_location_range(unsigned long start, unsigned long en
  */
 unsigned long ftrace_location(unsigned long ip)
 {
+	if (unlikely(!ftrace_pages_start))
+		return ftrace_search_mcount_ip(ip);
+
 	return ftrace_location_range(ip, ip);
 }
 
@@ -4733,6 +4738,18 @@ static int ftrace_cmp_ips(const void *a, const void *b)
 	return 0;
 }
 
+static int ftrace_cmp_ips_insn(const void *a, const void *b)
+{
+	const unsigned long *ipa = a;
+	const unsigned long *ipb = b;
+
+	if (*ipa >= *ipb + MCOUNT_INSN_SIZE)
+		return 1;
+	if (*ipa < *ipb)
+		return -1;
+	return 0;
+}
+
 static void ftrace_swap_ips(void *a, void *b, int size)
 {
 	unsigned long *ipa = a;
@@ -4770,6 +4787,27 @@ static void ftrace_sort_mcount_area(unsigned long *start, unsigned long *end)
 		kernel_mcount_sorted = true;
 }
 
+static unsigned long ftrace_search_mcount_ip(unsigned long ip)
+{
+	extern unsigned long __start_mcount_loc[];
+	extern unsigned long __stop_mcount_loc[];
+
+	unsigned long *mcount_start = __start_mcount_loc;
+	unsigned long *mcount_end = __stop_mcount_loc;
+	unsigned long count = mcount_end - mcount_start;
+	unsigned long *retval;
+
+	if (!kernel_mcount_sorted)
+		return 0;
+
+	retval = bsearch(&ip, mcount_start, count,
+			sizeof(unsigned long), ftrace_cmp_ips_insn);
+	if (!retval)
+		return 0;
+
+	return ftrace_call_adjust(ip);
+}
+
 static int ftrace_process_locs(struct module *mod,
 			       unsigned long *start,
 			       unsigned long *end)
-- 
1.8.4

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