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Subjectperf tools: interface for improved PEBS ABI can accept wrong parameter
For the commit: ab60834 perf, x86: Improve the PEBS ABI
The precise_ip is restricted to 2 bits. The values larger than 3 are truncated less or equal to 3.
This can effectively restricted value passing to syscall. But the user space interface can accept other wrong values which are larger than 3 and lowest 2 bits are 0 can meet the requirement.

# Here is an example, Monitor "All branches" events on Sandybridge platform( Please refer to SDM 3B Table 30-21 to check Sandybridge specific events )

perf top -e r04c4:p # precise_ip = 1 , Correct
perf top -e r04c4:pp # precise_ip =2, Correct
perf top -e r04c4:ppp # not supported, Correct
perf top -e r04c4:pppppp # should not be supported, but after truncation , the number of 'p' treated as 2 which is accepted


diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index c816075..07d3cf9 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -216,6 +216,7 @@ struct perf_event_attr {
*
* See also PERF_RECORD_MISC_EXACT_IP
*/
+#define SAMPLE_IP_MAX 3
precise_ip : 2, /* skid constraint */
mmap_data : 1, /* non-exec mmap data */
sample_id_all : 1, /* sample_type all events */
diff --git a/tools/perf/util/parse-events.c b/tools/perf/util/parse-events.c
index 928918b..a2068cc 100644
--- a/tools/perf/util/parse-events.c
+++ b/tools/perf/util/parse-events.c
@@ -775,7 +775,10 @@ parse_event_modifier(const char **strp, struct perf_event_attr *attr)
attr->exclude_user = eu;
attr->exclude_kernel = ek;
attr->exclude_hv = eh;
- attr->precise_ip = precise;
+ if ( precise < SAMPLE_IP_MAX )
+ attr->precise_ip = precise;
+ else
+ return -1;

return 0;
}

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