linux-kernel - [PATCH 2/2] perf s390: Fix 'start' address of module's map

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Date:	Tue, 26 Jul 2016 18:07:35 -0300
From:	Arnaldo Carvalho de Melo <acme@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Song Shan Gong <gongss@...ux.vnet.ibm.com>,
	Christian Borntraeger <borntraeger@...ibm.com>,
	David Ahern <dsahern@...il.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: [PATCH 2/2] perf s390: Fix 'start' address of module's map

From: Song Shan Gong <gongss@...ux.vnet.ibm.com>

At present, when creating module's map, perf gets 'start' address by
parsing '/proc/modules', but it's the module base address, it isn't the
start address of the '.text' section.

In most arches, it's OK. But for s390, it places 'GOT' and 'PLT'
relocations before '.text' section. So there exists an offset between
module base address and '.text' section, which will incur wrong symbol
resolution for modules.

Fix this bug by getting 'start' address of module's map from parsing
'/sys/module/[module name]/sections/.text', not from '/proc/modules'.

Signed-off-by: Song Shan Gong <gongss@...ux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@...nel.org>
Cc: Christian Borntraeger <borntraeger@...ibm.com>
Cc: David Ahern <dsahern@...il.com>
Link: http://lkml.kernel.org/r/1469070651-6447-2-git-send-email-gongss@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@...hat.com>
---
 tools/perf/arch/s390/util/Build     |  2 ++
 tools/perf/arch/s390/util/machine.c | 19 +++++++++++++++++++
 tools/perf/util/machine.c           |  8 ++++++++
 tools/perf/util/machine.h           |  1 +
 4 files changed, 30 insertions(+)
 create mode 100644 tools/perf/arch/s390/util/machine.c

diff --git a/tools/perf/arch/s390/util/Build b/tools/perf/arch/s390/util/Build
index 8a61372bb47a..5bd7b9260cc0 100644
--- a/tools/perf/arch/s390/util/Build
+++ b/tools/perf/arch/s390/util/Build
@@ -2,3 +2,5 @@ libperf-y += header.o
 libperf-y += kvm-stat.o
 
 libperf-$(CONFIG_DWARF) += dwarf-regs.o
+
+libperf-y += machine.o
diff --git a/tools/perf/arch/s390/util/machine.c b/tools/perf/arch/s390/util/machine.c
new file mode 100644
index 000000000000..b9a95a1a8e69
--- /dev/null
+++ b/tools/perf/arch/s390/util/machine.c
@@ -0,0 +1,19 @@
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include "util.h"
+#include "machine.h"
+#include "api/fs/fs.h"
+
+int arch__fix_module_text_start(u64 *start, const char *name)
+{
+	char path[PATH_MAX];
+
+	snprintf(path, PATH_MAX, "module/%.*s/sections/.text",
+				(int)strlen(name) - 2, name + 1);
+
+	if (sysfs__read_ull(path, (unsigned long long *)start) < 0)
+		return -1;
+
+	return 0;
+}
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index bc2cdbd09a25..cb6388dbdd98 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1093,12 +1093,20 @@ static int machine__set_modules_path(struct machine *machine)
 
 	return map_groups__set_modules_path_dir(&machine->kmaps, modules_path, 0);
 }
+int __weak arch__fix_module_text_start(u64 *start __maybe_unused,
+				const char *name __maybe_unused)
+{
+	return 0;
+}
 
 static int machine__create_module(void *arg, const char *name, u64 start)
 {
 	struct machine *machine = arg;
 	struct map *map;
 
+	if (arch__fix_module_text_start(&start, name) < 0)
+		return -1;
+
 	map = machine__findnew_module_map(machine, start, name);
 	if (map == NULL)
 		return -1;
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index 41ac9cfd416b..20739f746bc4 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -216,6 +216,7 @@ struct symbol *machine__find_kernel_function_by_name(struct machine *machine,
 
 struct map *machine__findnew_module_map(struct machine *machine, u64 start,
 					const char *filename);
+int arch__fix_module_text_start(u64 *start, const char *name);
 
 int __machine__load_kallsyms(struct machine *machine, const char *filename,
 			     enum map_type type, bool no_kcore, symbol_filter_t filter);
-- 
2.7.4