linux-kernel - [PATCH 2/3] samples/hw_breakpoint: Drop use of kallsyms_lookup

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Date:   Fri, 21 Feb 2020 11:44:03 +0000
From:   Will Deacon <will@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     kernel-team@...roid.com, akpm@...ux-foundation.org,
        Will Deacon <will@...nel.org>,
        "K . Prasad" <prasad@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Quentin Perret <qperret@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [PATCH 2/3] samples/hw_breakpoint: Drop use of kallsyms_lookup_name()

The 'data_breakpoint' test code is the only modular user of
kallsyms_lookup_name(), which was exported as part of fixing the test in
f60d24d2ad04 ("hw-breakpoints: Fix broken hw-breakpoint sample module").

In preparation for un-exporting this symbol, switch the test over to
using __symbol_get(), which can be used to place breakpoints on exported
symbols.

Cc: K.Prasad <prasad@...ux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Christoph Hellwig <hch@....de>
Cc: Quentin Perret <qperret@...gle.com>
Signed-off-by: Will Deacon <will@...nel.org>
---
 samples/hw_breakpoint/data_breakpoint.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
index 469b36f93696..418c46fe5ffc 100644
--- a/samples/hw_breakpoint/data_breakpoint.c
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -23,7 +23,7 @@
 
 struct perf_event * __percpu *sample_hbp;
 
-static char ksym_name[KSYM_NAME_LEN] = "pid_max";
+static char ksym_name[KSYM_NAME_LEN] = "jiffies";
 module_param_string(ksym, ksym_name, KSYM_NAME_LEN, S_IRUGO);
 MODULE_PARM_DESC(ksym, "Kernel symbol to monitor; this module will report any"
 			" write operations on the kernel symbol");
@@ -41,9 +41,13 @@ static int __init hw_break_module_init(void)
 {
 	int ret;
 	struct perf_event_attr attr;
+	void *addr = __symbol_get(ksym_name);
+
+	if (!addr)
+		return -ENXIO;
 
 	hw_breakpoint_init(&attr);
-	attr.bp_addr = kallsyms_lookup_name(ksym_name);
+	attr.bp_addr = (unsigned long)addr;
 	attr.bp_len = HW_BREAKPOINT_LEN_4;
 	attr.bp_type = HW_BREAKPOINT_W;
 
@@ -66,6 +70,7 @@ static int __init hw_break_module_init(void)
 static void __exit hw_break_module_exit(void)
 {
 	unregister_wide_hw_breakpoint(sample_hbp);
+	symbol_put(ksym_name);
 	printk(KERN_INFO "HW Breakpoint for %s write uninstalled\n", ksym_name);
 }
 
-- 
2.25.0.265.gbab2e86ba0-goog