perf trace: Allow specifying index offset in strarrays

So that the index passed doesn't have to start at zero, being
decremented from an offset specified when declaring the strarray before
being used as the real array index.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-k1ce6uqyt4qar9edrj3mevod@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-trace.c

@@ -44,6 +44,7 @@ struct syscall_arg {
 };
 
 struct strarray {
+	int	    offset;
 	int	    nr_entries;
 	const char **entries;
 };
@@ -53,14 +54,20 @@ struct strarray {
 	.entries = array, \
 }
 
+#define DEFINE_STRARRAY_OFFSET(array, off) struct strarray strarray__##array = { \
+	.offset	    = off, \
+	.nr_entries = ARRAY_SIZE(array), \
+	.entries = array, \
+}
+
 static size_t syscall_arg__scnprintf_strarray(char *bf, size_t size,
 					      struct syscall_arg *arg)
 {
-	int idx = arg->val;
 	struct strarray *sa = arg->parm;
+	int idx = arg->val - sa->offset;
 
 	if (idx < 0 || idx >= sa->nr_entries)
-		return scnprintf(bf, size, "%d", idx);
+		return scnprintf(bf, size, "%d", arg->val);
 
 	return scnprintf(bf, size, "%s", sa->entries[idx]);
 }
@@ -288,8 +295,8 @@ static size_t syscall_arg__scnprintf_futex_op(char *bf, size_t size, struct sysc
 
 #define SCA_FUTEX_OP  syscall_arg__scnprintf_futex_op
 
-static const char *epoll_ctl_ops[] = { [1] = "ADD", "DEL", "MOD", };
-static DEFINE_STRARRAY(epoll_ctl_ops);
+static const char *epoll_ctl_ops[] = { "ADD", "DEL", "MOD", };
+static DEFINE_STRARRAY_OFFSET(epoll_ctl_ops, 1);
 
 static const char *itimers[] = { "REAL", "VIRTUAL", "PROF", };
 static DEFINE_STRARRAY(itimers);