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Subject[PATCH v4] tools/lib/traceevent: Separate out tep_strerror() for strerror_r() issues

From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>

While working on having PowerTop use libtracevent as a shared object
library, Tzvetomir hit "str_error_r not defined". This was added by commit
c3cec9e68f12d ("tools lib traceevent: Use str_error_r()") because
strerror_r() has two definitions, where one is GNU specific, and the other
is XSI complient. The strerror_r() is in a wrapper str_error_r() to keep the
code from having to worry about which compiler is being used.

The problem is that str_error_r() is external to libtraceevent, and not part
of the library. If it is used as a shared object then the tools using it
will need to define that function. I do not want that function defined in
libtraceevent itself, as it is out of scope for that library.

As there's only a single instance of this call, and its in the traceevent
library's own tep_strerror() function, we can copy what was done in perf,
and create yet another external file that undefs _GNU_SOURCE to use the more
portable version of the function. We don't need to worry about the errors
that strerror_r() returns. If the buffer isn't big enough, we simply
truncate it.

Link: http://lkml.kernel.org/r/20181002175539.2ac894c7@gandalf.local.home
Reported-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
tools/lib/traceevent/Build | 1 +
tools/lib/traceevent/event-parse.c | 30 ---------------------
tools/lib/traceevent/tep_strerror.c | 53 +++++++++++++++++++++++++++++++++++++
3 files changed, 54 insertions(+), 30 deletions(-)
create mode 100644 tools/lib/traceevent/tep_strerror.c

diff --git a/tools/lib/traceevent/Build b/tools/lib/traceevent/Build
index c681d0575d16..0050c145d806 100644
--- a/tools/lib/traceevent/Build
+++ b/tools/lib/traceevent/Build
@@ -4,6 +4,7 @@ libtraceevent-y += trace-seq.o
libtraceevent-y += parse-filter.o
libtraceevent-y += parse-utils.o
libtraceevent-y += kbuffer-parse.o
+libtraceevent-y += tep_strerror.o

plugin_jbd2-y += plugin_jbd2.o
plugin_hrtimer-y += plugin_hrtimer.o
diff --git a/tools/lib/traceevent/event-parse.c b/tools/lib/traceevent/event-parse.c
index 7980fc6c3bac..233179a712d6 100644
--- a/tools/lib/traceevent/event-parse.c
+++ b/tools/lib/traceevent/event-parse.c
@@ -18,7 +18,6 @@
#include <errno.h>
#include <stdint.h>
#include <limits.h>
-#include <linux/string.h>
#include <linux/time64.h>

#include <netinet/in.h>
@@ -6201,35 +6200,6 @@ enum tep_errno tep_parse_event(struct tep_handle *pevent, const char *buf,
return __parse_event(pevent, &event, buf, size, sys);
}

-#undef _PE
-#define _PE(code, str) str
-static const char * const tep_error_str[] = {
- TEP_ERRORS
-};
-#undef _PE
-
-int tep_strerror(struct tep_handle *pevent __maybe_unused,
- enum tep_errno errnum, char *buf, size_t buflen)
-{
- int idx;
- const char *msg;
-
- if (errnum >= 0) {
- str_error_r(errnum, buf, buflen);
- return 0;
- }
-
- if (errnum <= __TEP_ERRNO__START ||
- errnum >= __TEP_ERRNO__END)
- return -1;
-
- idx = errnum - __TEP_ERRNO__START - 1;
- msg = tep_error_str[idx];
- snprintf(buf, buflen, "%s", msg);
-
- return 0;
-}
-
int get_field_val(struct trace_seq *s, struct tep_format_field *field,
const char *name, struct tep_record *record,
unsigned long long *val, int err)
diff --git a/tools/lib/traceevent/tep_strerror.c b/tools/lib/traceevent/tep_strerror.c
new file mode 100644
index 000000000000..4ac26445b2f6
--- /dev/null
+++ b/tools/lib/traceevent/tep_strerror.c
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: LGPL-2.1
+#undef _GNU_SOURCE
+#include <string.h>
+#include <stdio.h>
+
+#include "event-parse.h"
+
+#undef _PE
+#define _PE(code, str) str
+static const char * const tep_error_str[] = {
+ TEP_ERRORS
+};
+#undef _PE
+
+/*
+ * The tools so far have been using the strerror_r() GNU variant, that returns
+ * a string, be it the buffer passed or something else.
+ *
+ * But that, besides being tricky in cases where we expect that the function
+ * using strerror_r() returns the error formatted in a provided buffer (we have
+ * to check if it returned something else and copy that instead), breaks the
+ * build on systems not using glibc, like Alpine Linux, where musl libc is
+ * used.
+ *
+ * So, introduce yet another wrapper, str_error_r(), that has the GNU
+ * interface, but uses the portable XSI variant of strerror_r(), so that users
+ * rest asured that the provided buffer is used and it is what is returned.
+ */
+int tep_strerror(struct tep_handle *tep __maybe_unused,
+ enum tep_errno errnum, char *buf, size_t buflen)
+{
+ const char *msg;
+ int idx;
+
+ if (!buflen)
+ return 0;
+
+ if (errnum >= 0) {
+ int err = strerror_r(errnum, buf, buflen);
+ buf[buflen - 1] = 0;
+ return err;
+ }
+
+ if (errnum <= __TEP_ERRNO__START ||
+ errnum >= __TEP_ERRNO__END)
+ return -1;
+
+ idx = errnum - __TEP_ERRNO__START - 1;
+ msg = tep_error_str[idx];
+ snprintf(buf, buflen, "%s", msg);
+
+ return 0;
+}
--
2.13.6
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