[SRU][Disco][PATCH 2/3] perf record: Fix module size on s390

Kleber Sacilotto de Souza kleber.souza at canonical.com
Fri Aug 23 12:07:19 UTC 2019

From: Thomas Richter <tmricht at linux.ibm.com>

BugLink: https://bugs.launchpad.net/bugs/1828166

On s390 the modules loaded in memory have the text segment located after
the GOT and Relocation table. This can be seen with this output:

  [root at m35lp76 perf]# fgrep qeth /proc/modules
  qeth 151552 1 qeth_l2, Live 0x000003ff800b2000
  [root at m35lp76 perf]# cat /sys/module/qeth/sections/.text
  [root at m35lp76 perf]#

There is an offset of 0x1990 bytes. The size of the qeth module is
151552 bytes (0x25000 in hex).

The location of the GOT/relocation table at the beginning of a module is
unique to s390.

commit 203d8a4aa6ed ("perf s390: Fix 'start' address of module's map")
adjusts the start address of a module in the map structures, but does
not adjust the size of the modules. This leads to overlapping of module
maps as this example shows:

[root at m35lp76 perf] # ./perf report -D
     0 0 0xfb0 [0xa0]: PERF_RECORD_MMAP -1/0: [0x3ff800b3990(0x25000)
          @ 0]:  x /lib/modules/.../qeth.ko.xz
     0 0 0x1050 [0xb0]: PERF_RECORD_MMAP -1/0: [0x3ff800d85a0(0x8000)
          @ 0]:  x /lib/modules/.../ip6_tables.ko.xz

The module qeth.ko has an adjusted start address modified to b3990, but
its size is unchanged and the module ends at 0x3ff800d8990.  This end
address overlaps with the next modules start address of 0x3ff800d85a0.

When the size of the leading GOT/Relocation table stored in the
beginning of the text segment (0x1990 bytes) is subtracted from module
qeth end address, there are no overlaps anymore:

   0x3ff800d8990 - 0x1990 = 0x0x3ff800d7000

which is the same as

   0x3ff800b2000 + 0x25000 = 0x0x3ff800d7000.

To fix this issue, also adjust the modules size in function
arch__fix_module_text_start(). Add another function parameter named size
and reduce the size of the module when the text segment start address is

Output after:
     0 0 0xfb0 [0xa0]: PERF_RECORD_MMAP -1/0: [0x3ff800b3990(0x23670)
          @ 0]:  x /lib/modules/.../qeth.ko.xz
     0 0 0x1050 [0xb0]: PERF_RECORD_MMAP -1/0: [0x3ff800d85a0(0x7a60)
          @ 0]:  x /lib/modules/.../ip6_tables.ko.xz

Reported-by: Stefan Liebler <stli at linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht at linux.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens at de.ibm.com>
Cc: Hendrik Brueckner <brueckner at linux.ibm.com>
Cc: Vasily Gorbik <gor at linux.ibm.com>
Cc: stable at vger.kernel.org
Fixes: 203d8a4aa6ed ("perf s390: Fix 'start' address of module's map")
Link: http://lkml.kernel.org/r/20190724122703.3996-1-tmricht@linux.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme at redhat.com>
(cherry picked from commit 12a6d2940b5f02b4b9f71ce098e3bb02bc24a9ea)
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
 tools/perf/arch/s390/util/machine.c | 14 +++++++++++++-
 tools/perf/util/machine.c           |  3 ++-
 tools/perf/util/machine.h           |  2 +-
 3 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/tools/perf/arch/s390/util/machine.c b/tools/perf/arch/s390/util/machine.c
index a19690a17291..de26b1441a48 100644
--- a/tools/perf/arch/s390/util/machine.c
+++ b/tools/perf/arch/s390/util/machine.c
@@ -7,7 +7,7 @@
 #include "api/fs/fs.h"
 #include "debug.h"
-int arch__fix_module_text_start(u64 *start, const char *name)
+int arch__fix_module_text_start(u64 *start, u64 *size, const char *name)
 	u64 m_start = *start;
 	char path[PATH_MAX];
@@ -17,6 +17,18 @@ int arch__fix_module_text_start(u64 *start, const char *name)
 	if (sysfs__read_ull(path, (unsigned long long *)start) < 0) {
 		pr_debug2("Using module %s start:%#lx\n", path, m_start);
 		*start = m_start;
+	} else {
+		/* Successful read of the modules segment text start address.
+		 * Calculate difference between module start address
+		 * in memory and module text segment start address.
+		 * For example module load address is 0x3ff8011b000
+		 * (from /proc/modules) and module text segment start
+		 * address is 0x3ff8011b870 (from file above).
+		 *
+		 * Adjust the module size and subtract the GOT table
+		 * size located at the beginning of the module.
+		 */
+		*size -= (*start - m_start);
 	return 0;
diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 596db1daee35..d3a5890b5047 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1295,6 +1295,7 @@ 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,
+				u64 *size __maybe_unused,
 				const char *name __maybe_unused)
 	return 0;
@@ -1306,7 +1307,7 @@ 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)
+	if (arch__fix_module_text_start(&start, &size, name) < 0)
 		return -1;
 	map = machine__findnew_module_map(machine, start, name);
diff --git a/tools/perf/util/machine.h b/tools/perf/util/machine.h
index a5d1da60f751..85881aad1b75 100644
--- a/tools/perf/util/machine.h
+++ b/tools/perf/util/machine.h
@@ -219,7 +219,7 @@ struct symbol *machine__find_kernel_symbol_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 arch__fix_module_text_start(u64 *start, u64 *size, const char *name);
 int machine__load_kallsyms(struct machine *machine, const char *filename);

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