[RFC PATCH V2] s390/perf: fix 'start' address of module's map

[Song Shan Gong]

At preset, when creating module's map, perf gets 'start' address by parsing
'/proc/modules', but it's module base address, isn't the start address of
'.text' section. In most archs, 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@xxxxxxxxxxxxxxxxxx>
---
 tools/perf/arch/s390/util/Build          |  2 ++
 tools/perf/arch/s390/util/sym-handling.c | 27 +++++++++++++++++++++++++++
 tools/perf/util/machine.c                |  8 ++++++++
 tools/perf/util/machine.h                |  1 +
 4 files changed, 38 insertions(+)
 create mode 100644 tools/perf/arch/s390/util/sym-handling.c

diff --git a/tools/perf/arch/s390/util/Build b/tools/perf/arch/s390/util/Build
index 8a61372..5e322ed 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 += sym-handling.o
diff --git a/tools/perf/arch/s390/util/sym-handling.c b/tools/perf/arch/s390/util/sym-handling.c
new file mode 100644
index 0000000..ff51336
--- /dev/null
+++ b/tools/perf/arch/s390/util/sym-handling.c
@@ -0,0 +1,27 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.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];
+	char *module_name = NULL;
+	int len;
+
+	if (!(module_name = strdup(name)))
+		return -1;
+
+	len = strlen(module_name);
+	module_name[len - 1] = '\0';
+	snprintf(path, PATH_MAX, "module/%s/sections/.text",
+				module_name + 1);
+
+	if (sysfs__read_ull(path, (unsigned long long *)start) < 0) {
+		free(module_name);
+		return -1;
+	}
+	return 0;
+}
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index b177218..97cc9f0 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1091,12 +1091,20 @@ 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 41ac9cf..20739f7 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);
-- 
2.3.0