perf tools: Fix kernel version error in ubuntu

On ubuntu the internal kernel version code is different from what can
be retrived from uname:

 $ uname -r
 4.4.0-47-generic
 $ cat /lib/modules/`uname -r`/build/include/generated/uapi/linux/version.h
 #define LINUX_VERSION_CODE 263192
 #define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))
 $ cat /lib/modules/`uname -r`/build/include/generated/utsrelease.h
 #define UTS_RELEASE "4.4.0-47-generic"
 #define UTS_UBUNTU_RELEASE_ABI 47
 $ cat /proc/version_signature
 Ubuntu 4.4.0-47.68-generic 4.4.24

The macro LINUX_VERSION_CODE is set to 4.4.24 (263192 == 0x40418), but
`uname -r` reports 4.4.0.

This mismatch causes LINUX_VERSION_CODE macro passed to BPF script become
an incorrect value, results in magic failure in BPF loading:

 $ sudo ./buildperf/perf record -e ./tools/perf/tests/bpf-script-example.c ls
 event syntax error: './tools/perf/tests/bpf-script-example.c'
                      \___ Failed to load program for unknown reason

According to Ubuntu document (https://wiki.ubuntu.com/Kernel/FAQ), the
correct kernel version can be retrived through /proc/version_signature, which
is ubuntu specific.

This patch checks the existance of /proc/version_signature, and returns
version number through parsing this file instead of uname. Version string
is untouched (value returns from uname) because `uname -r` is required
to be consistence with path of kbuild directory in /lib/module.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Cc: Alexei Starovoitov <ast@fb.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/r/20161115040617.69788-2-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 53 insertions, 2 deletions

diff --git a/tools/perf/util/util.c b/tools/perf/util/util.c
index 5bbd1f609f1f..67ac765da27a 100644
--- a/tools/perf/util/util.c
+++ b/tools/perf/util/util.c
@@ -637,12 +637,63 @@ bool find_process(const char *name)
         return ret ? false : true;
 }
 
+static int
+fetch_ubuntu_kernel_version(unsigned int *puint)
+{
+        ssize_t len;
+        size_t line_len = 0;
+        char *ptr, *line = NULL;
+        int version, patchlevel, sublevel, err;
+        FILE *vsig = fopen("/proc/version_signature", "r");
+
+        if (!vsig) {
+                pr_debug("Open /proc/version_signature failed: %s\n",
+                         strerror(errno));
+                return -1;
+        }
+
+        len = getline(&line, &line_len, vsig);
+        fclose(vsig);
+        err = -1;
+        if (len <= 0) {
+                pr_debug("Reading from /proc/version_signature failed: %s\n",
+                         strerror(errno));
+                goto errout;
+        }
+
+        ptr = strrchr(line, ' ');
+        if (!ptr) {
+                pr_debug("Parsing /proc/version_signature failed: %s\n", line);
+                goto errout;
+        }
+
+        err = sscanf(ptr + 1, "%d.%d.%d",
+                     &version, &patchlevel, &sublevel);
+        if (err != 3) {
+                pr_debug("Unable to get kernel version from /proc/version_signature '%s'\n",
+                         line);
+                goto errout;
+        }
+
+        if (puint)
+                *puint = (version << 16) + (patchlevel << 8) + sublevel;
+        err = 0;
+errout:
+        free(line);
+        return err;
+}
+
 int
 fetch_kernel_version(unsigned int *puint, char *str,
                      size_t str_size)
 {
         struct utsname utsname;
         int version, patchlevel, sublevel, err;
+        bool int_ver_ready = false;
+
+        if (access("/proc/version_signature", R_OK) == 0)
+                if (!fetch_ubuntu_kernel_version(puint))
+                        int_ver_ready = true;
 
         if (uname(&utsname))
                 return -1;
@@ -656,12 +707,12 @@ fetch_kernel_version(unsigned int *puint, char *str,
                      &version, &patchlevel, &sublevel);
 
         if (err != 3) {
-                pr_debug("Unablt to get kernel version from uname '%s'\n",
+                pr_debug("Unable to get kernel version from uname '%s'\n",
                          utsname.release);
                 return -1;
         }
 
-        if (puint)
+        if (puint && !int_ver_ready)
                 *puint = (version << 16) + (patchlevel << 8) + sublevel;
         return 0;
 }