Swift framework with a C lib inside: Got segmentation fault during working with C types - ios

Question

I'm building swift wrapper for PJSIP C lib.
I faced with a strange behaviour of memory alloc/free.
This func produces seg fault error [old plain NULL pointer]:
pjsua_msg_data is a C struct
static func makePj(fromHeaders headers: [SipHeader],
pool: inout UnsafeMutablePointer<pj_pool_t>) -> pjsua_msg_data {
var msgData = pjsua_msg_data()
pjsua_msg_data_init(&msgData)
pj_list_init(&msgData.hdr_list)
for header in headers {
let pjHeader = header.toPj(pool: &pool)
pj_list_push_back(&msgData.hdr_list, pjHeader)
}
return msgData
}
This implementation works (difference is that msgData as inout param)
static func makePj(fromHeaders headers: [SipHeader],
msgData: inout pjsua_msg_data,
pool: inout UnsafeMutablePointer<pj_pool_t>) {
pjsua_msg_data_init(&msgData)
pj_list_init(&msgData.hdr_list)
for header in headers {
let pjHeader = header.toPj(pool: &pool)
pj_list_push_back(&msgData.hdr_list, pjHeader)
}
}
Usage
var msgData = pjsua_msg_data()
var pool = try API.shared.createMemPool("pool", block: 4096, increment: 1024)
defer { try? API.shared.releaseMemPool(pool) }
if !headers.isEmpty {
// - usage of working implementations
//MessageData.makePj(fromHeaders: headers,
// msgData: &msgData,
// pool: &pool)
// - seg fault implementation usage
msgData = MessageData.makePj(fromHeaders: headers,
pool: &pool)
}
try callPJSUA {
pjsua_call_make_call(accountId,
&uriStr,
&callSetting,
nil,
&msgData,
&callId)
}
Little bit about framework:
it's a just Swift wrapper under C lib.
This framework then linked to the iOS app
Question:
I don't understand why inout param works but returning value doesn't.
Can I change this swift compiler behaviour? Build settings or smth else ?
Exception:
Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Subtype: KERN_INVALID_ADDRESS at 0x0000000000000000
Exception Codes: 0x0000000000000001, 0x0000000000000000
VM Region Info: 0 is not in any region. Bytes before following region: 4365074432
REGION TYPE START - END [ VSIZE] PRT/MAX SHRMOD REGION DETAIL
UNUSED SPACE AT START
--->
__TEXT 1042dc000-1056ec000 [ 20.1M] r-x/r-x SM=COW ...app/CallScape
Exception Note: EXC_CORPSE_NOTIFY
Termination Reason: SIGNAL 11 Segmentation fault: 11
Terminating Process: exc handler [2095]
Thread 11 name: Dispatch queue: working.queue
Thread 11 Crashed:
0 SDK 0x10d3f3f28 pjsip_hdr_clone + 36
1 SDK 0x10d6d7454 pjsua_msg_data_clone + 280
2 SDK 0x10d6d7454 pjsua_msg_data_clone + 280
3 SDK 0x10d6cc4c8 pjsua_call_make_call + 1276
4 SDK 0x10d38a710 specialized CallAPI.make(_:destinationURI:setting:headers:) + 1268
5 SDK 0x10d389de8 protocol witness for CallAPI.make(_:destinationURI:setting:headers:) in conformance API + 12
6 SDK 0x10d39c8a8 Call.make(to:setting:headers:) + 152