X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=liblttng-ust%2Flttng-context-perf-counters.c;fp=liblttng-ust%2Flttng-context-perf-counters.c;h=61149d061310af0ec8f8f15902b36bff72bb2c15;hb=e83cec0b52e0c2c1939d8b9c8aa11be3c7a672fd;hp=83b371c5ba91431f47f44ce6880a4087d2e0244c;hpb=f8dc4e455a3aa1745a5b789fc707182b7b5439e0;p=lttng-ust.git

diff --git a/liblttng-ust/lttng-context-perf-counters.c b/liblttng-ust/lttng-context-perf-counters.c
index 83b371c5..61149d06 100644
--- a/liblttng-ust/lttng-context-perf-counters.c
+++ b/liblttng-ust/lttng-context-perf-counters.c
@@ -110,11 +110,17 @@ uint64_t read_perf_counter(struct perf_event_mmap_page *pc)
 		cmm_barrier();
 
 		idx = pc->index;
-		if (idx)
-			count = pc->offset + rdpmc(idx - 1);
-		else
+		if (idx) {
+			int64_t pmcval;
+
+			pmcval = rdpmc(idx - 1);
+			/* Sign-extend the pmc register result. */
+			pmcval <<= 64 - pc->pmc_width;
+			pmcval >>= 64 - pc->pmc_width;
+			count = pc->offset + pmcval;
+		} else {
 			count = 0;
-
+		}
 		cmm_barrier();
 	} while (CMM_LOAD_SHARED(pc->lock) != seq);