CSN1 decoding: add test to show bug in CSN_LEFT_ALIGNED_VAR_BMP
CSN1 decoding currently contains an attempted read past vector boundaries in
case of a starting bit offset != 0, so that the last amount of bits read should
be < 8. In the case of CSN_LEFT_ALIGNED_VAR_BMP, the mod-8 calculation is
flawed, and in what should be the final step of reading n < 8 bits, 8 bits are
read instead of n (with an extraneous read of n bits following after that).
This leads to -EINVAL being returned by bitvec_get_bit_pos() and bogus
resulting data.
Add testCsnLeftAlignedVarBmpBounds() in RLCMACTest.cpp to show and expect this
bug. The test's expectation shall be corrected along with the bug fix in a
subsequent commit.
Related: OS#1805
Tweaked-by: Neels Hofmeyr <nhofmeyr@sysmocom.de>
Change-Id: I4641f5d1d49f66cb1a5cd813befb3a2a266001b0
diff --git a/tests/rlcmac/RLCMACTest.cpp b/tests/rlcmac/RLCMACTest.cpp
index 466b89e..f633dd8 100644
--- a/tests/rlcmac/RLCMACTest.cpp
+++ b/tests/rlcmac/RLCMACTest.cpp
@@ -30,6 +30,7 @@
#include "pcu_vty.h"
#include <osmocom/vty/telnet_interface.h>
#include <osmocom/vty/logging.h>
+#include <osmocom/core/utils.h>
#include <osmocom/core/application.h>
}
using namespace std;
@@ -211,6 +212,26 @@
bitvec_free(resultVector);
}
+void testCsnLeftAlignedVarBmpBounds()
+{
+ bitvec *vector = bitvec_alloc(23);
+
+ bitvec_unhex(vector, "40200bffd161003e0e519ffffffb800000000000000000");
+ RlcMacUplink_t data;
+
+ EGPRS_AckNack_Desc_t *urbb =
+ &data.u.Egprs_Packet_Downlink_Ack_Nack.EGPRS_AckNack.Desc;
+ decode_gsm_rlcmac_uplink(vector, &data);
+
+ /*
+ * TODO: URBB len is decoded as 102 bits. So 96 + 6 bits = 12 bytes + 6
+ * bits should be decoded. The 13th byte should end up as 0x00, but we
+ * see data coming from bitvec_get_bit_pos() returning -EINVAL.
+ */
+ OSMO_ASSERT(!strcmp(osmo_hexdump(urbb->URBB, 13),
+ "7f ff ff ee 00 00 00 00 00 00 00 00 ea "));
+}
+
int main(int argc, char *argv[])
{
osmo_init_logging(&gprs_log_info);
@@ -218,5 +239,5 @@
//printSizeofRLCMAC();
testRlcMacDownlink();
testRlcMacUplink();
-
+ testCsnLeftAlignedVarBmpBounds();
}