Cleanup the code flow of dso__find_kallsyms() to remove
redundant checking code and add some comment for readability.
Signed-off-by: Masami Hiramatsu <mhira...@kernel.org>
---
Changes in v8:
- Add comments why we can't use access(R_OK) for /proc/kcore access.
---
tools/perf/util/symbol.c | 68 ++++++++++++++++++++++++----------------------
1 file changed, 35 insertions(+), 33 deletions(-)
diff --git a/tools/perf/util/symbol.c b/tools/perf/util/symbol.c
index 2252b54..abda8ba 100644
--- a/tools/perf/util/symbol.c
+++ b/tools/perf/util/symbol.c
@@ -1641,6 +1641,20 @@ static int find_matching_kcore(struct map *map, char
*dir, size_t dir_sz)
return ret;
}
+/*
+ * Use open(O_RDONLY) to check readability directly instead of access(R_OK)
+ * since access(R_OK) only checks with real UID/GID but open() use effective
+ * UID/GID and actual capabilities (e.g. /proc/kcore requires CAP_SYS_RAWIO).
+ */
+static bool filename__readable(const char *file)
+{
+ int fd = open(file, O_RDONLY);
+ if (fd < 0)
+ return false;
+ close(fd);
+ return true;
+}
+
static char *dso__find_kallsyms(struct dso *dso, struct map *map)
{
u8 host_build_id[BUILD_ID_SIZE];
@@ -1660,45 +1674,36 @@ static char *dso__find_kallsyms(struct dso *dso, struct
map *map)
sizeof(host_build_id)) == 0)
is_host = dso__build_id_equal(dso, host_build_id);
- build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
-
- scnprintf(path, sizeof(path), "%s/%s/%s", buildid_dir,
- DSO__NAME_KCORE, sbuild_id);
-
- /* Use /proc/kallsyms if possible */
+ /* Try a fast path for /proc/kallsyms if possible */
if (is_host) {
- DIR *d;
- int fd;
-
- /* If no cached kcore go with /proc/kallsyms */
- d = opendir(path);
- if (!d)
- goto proc_kallsyms;
- closedir(d);
-
/*
- * Do not check the build-id cache, until we know we cannot use
- * /proc/kcore.
+ * Do not check the build-id cache, unless we know we cannot use
+ * /proc/kcore or module maps don't match to /proc/kallsyms.
+ * To check readability of /proc/kcore, do not use access(R_OK)
+ * since /proc/kcore requires CAP_SYS_RAWIO to read and access
+ * can't check it.
*/
- fd = open("/proc/kcore", O_RDONLY);
- if (fd != -1) {
- close(fd);
- /* If module maps match go with /proc/kallsyms */
- if (!validate_kcore_addresses("/proc/kallsyms", map))
- goto proc_kallsyms;
- }
-
- /* Find kallsyms in build-id cache with kcore */
- if (!find_matching_kcore(map, path, sizeof(path)))
- return strdup(path);
-
- goto proc_kallsyms;
+ if (filename__readable("/proc/kcore") &&
+ !validate_kcore_addresses("/proc/kallsyms", map))
+ goto proc_kallsyms;
}
+ build_id__sprintf(dso->build_id, sizeof(dso->build_id), sbuild_id);
+
/* Find kallsyms in build-id cache with kcore */
+ scnprintf(path, sizeof(path), "%s/%s/%s",
+ buildid_dir, DSO__NAME_KCORE, sbuild_id);
+
if (!find_matching_kcore(map, path, sizeof(path)))
return strdup(path);
+ /* Use current /proc/kallsyms if possible */
+ if (is_host) {
+proc_kallsyms:
+ return strdup("/proc/kallsyms");
+ }
+
+ /* Finally, find a cache of kallsyms */
scnprintf(path, sizeof(path), "%s/%s/%s",
buildid_dir, DSO__NAME_KALLSYMS, sbuild_id);
@@ -1709,9 +1714,6 @@ static char *dso__find_kallsyms(struct dso *dso, struct
map *map)
}
return strdup(path);
-
-proc_kallsyms:
- return strdup("/proc/kallsyms");
}
static int dso__load_kernel_sym(struct dso *dso, struct map *map,
