commit 93ad3fd9b9aed26a609551c06a80db0e276eb4f1
author Vadim Yanitskiy <vyanitskiy@sysmocom.de> Sat May 23 18:17:19 2020 +0700
committer Vadim Yanitskiy <vyanitskiy@sysmocom.de> Sat May 23 19:26:58 2020 +0700
tree 10e66f12cd5093a32bc407d6be510b08f8af8b0a
parent 0614e9333fb5072640ba9939a28ffc1588cfe5bd

csn1: fix: never use enumerated types in codec structures

I faced a problem while working on EGPRS Packet Channel Request
coding support: the unit test I wrote for it was passing when
compiled with AddressSanitizer, but failing when compiled
without it o_O. Somehow this was observed only with GCC 10.

Here is a part the standard output diff for that unit test:

   *** testEGPRSPktChReq ***
   decode_egprs_pkt_ch_req(0x2b5) returns 0
  - ==> One Phase Access
  + ==> unknown 0xdd5f4e00
   decode_egprs_pkt_ch_req(0x14a) returns 0
  - ==> One Phase Access
  + ==> unknown 0xdd5f4e00
   decode_egprs_pkt_ch_req(0x428) returns 0
  - ==> Short Access
  + ==> unknown 0xdd5f4e01

At the same time, debug output of the CSN.1 decoder looked fine.
So WYSINWYG (What You See Is *NOT* What You Get)! As it turned
out, this was happening because I used an enumerated type to
represent the sub-type of EGPRS Packet Channel Request.

  typedef struct
  {
    EGPRS_PacketChannelRequestType_t      Type; // <-- enum
    EGPRS_PacketChannelRequestContent_t	  Content;
  } EGPRS_PacketChannelRequest_t;

The problem is that length of an enumerated field, more precisely
the amount of bytes it takes in the memory, is compiler/machine
dependent. While the CSN.1 decoder assumes that the field holding
sequential number of the chosen element is one octet long, so its
address is getting casted to (guint8 *) and the value is written
to the first MSB.

  // csnStreamDecoder(), case CSN_CHOICE:
  pui8  = pui8DATA(data, pDescr->offset);
  *pui8 = i; // [ --> xx .. .. .. ]

Let's make sure that none of the existing RLC/MAC definitions is
using enumerated types, and add a warning comment to CSN_CHOICE.

Affected CSN.1 definitions (unit test output adjusted):

  - Additional_access_technologies_struct_t,
  - Channel_Request_Description_t.

Change-Id: I917a40647480c6f6f3b0e68674ce9894379a9e7f