Question
FreeRTOS + LWIP + MDNS
I have an STM32H735 Discovery Kit and am running the example LWIP code from STM32H7-LwIP-Examples/STM32H735_Disco_ETH. This works great. But, when I add MDNS, I get a very curious crash.
I enabled MDNS in CubeMX, and then created a new thread to wait for an address to be assigned by DHCP before initializing MDNS:
void mdns_thread(void *argument) {
mdns_resp_init();
while(!dhcp_supplied_address(&gnetif)) {
vTaskDelay(1000/ portTICK_PERIOD_MS);
}
LOCK_TCPIP_CORE();
mdns_resp_add_netif(&gnetif, "scion", 60);
/*
mdns_resp_add_service(&gnetif, "_scion", "_scion", DNSSD_PROTO_UDP, 9000, 3600, srv_txt, NULL);
mdns_resp_announce(&gnetif);
*/
UNLOCK_TCPIP_CORE();
while (1) {
vTaskDelay(500/ portTICK_PERIOD_MS);
}
}With the thread created as:
osThreadAttr_t attributes;
memset(&attributes, 0x0, sizeof(osThreadAttr_t));
attributes.name = "MDNS";
attributes.stack_size = 512;
attributes.priority = osPriorityNormal;
osThreadNew(mdns_thread, &gnetif, &attributes);The issue occurs when I uncomment mdns_resp_add_netif(), as per the code snippet above.
Enabling mdns_resp_add_netif(&gnetif, "scion", 60); causes the program to hang on:
configASSERT( pxQueue->uxItemSize == 0 );Inside xQueueSemaphoreTake:
Thread #1 [main] 1 [core: 0] (Suspended : Signal : SIGINT:Interrupt)
xQueueSemaphoreTake() at queue.c:1,433 0x8005210
osMutexAcquire() at cmsis_os2.c:1,416 0x8004586
sys_mutex_lock() at sys_arch.c:435 0x8011f9e
mem_trim() at mem.c:751 0x80089de
pbuf_realloc() at pbuf.c:444 0x800973e
mdns_send_outpacket() at mdns.c:1,485 0x80078c4
mdns_send_probe() at mdns.c:2,005 0x8007abe
mdns_probe() at mdns.c:2,035 0x800833c
sys_check_timeouts() at timeouts.c:390 0x800e276
tcpip_timeouts_mbox_fetch() at tcpip.c:98 0x8006b02
<...more frames...>This pxQueue is supposed to be a semaphore, but the data inside it has been corrupt.
p &pxQueue->uxItemSize
$3 = (UBaseType_t *) 0x24002e90 <ucHeap+3088>So, let's set a watch on that in GBD and restart:
watch *(uint32_t *)0x24002e90
Hardware watchpoint 6: *(uint32_t *)0x24002e90It first breaks in prvInitialiseNewQueue, which is totally kosher. Continuing execution and it breaks here:
Program received signal SIGTRAP, Trace/breakpoint trap.
0x08006d06 in mdns_readname_loop (p=p@entry=0x30000470, offset=offset@entry=12, domain=domain@entry=0x24002ec4 <ucHeap+3140>, depth=depth@entry=0)
Thread #1 [main] 1 [core: 0] (Suspended : Signal : SIGTRAP:Trace/breakpoint trap)
mdns_readname_loop() at mdns.c:360 0x8006d06
mdns_readname() at mdns.c:424 0x8006e12
mdns_compress_domain() at mdns.c:798 0x8006e12
mdns_compress_domain() at mdns.c:842 0x8006ee4
mdns_write_domain() at mdns.c:849 0x8006ee4
mdns_add_question() at mdns.c:923 0x8006fb4
mdns_add_answer() at mdns.c:1,001 0x8007086
mdns_add_a_answer() at mdns.c:1,176 0x80073fa
mdns_send_outpacket() at mdns.c:1,320 0x80079e8
mdns_send_probe() at mdns.c:2,005 0x8007abe
<...more frames...>Look at the psp:
info registers
r0 0x30000470 805307504
r1 0xc 12
r2 0x24002ec4 603991748
r3 0x0 0
r4 0x30000470 805307504
r5 0xc 12
r6 0x2400307c 603992188
r7 0xd 13
r8 0x0 0
r9 0x24003204 603992580
r10 0xa5a5a5a5 2779096485
r11 0x2400307c 603992188
r12 0x2e 46
sp 0x24002e90 0x24002e90 <ucHeap+3088>
lr 0x8006e13 134245907
pc 0x8006d06 0x8006d06 <mdns_readname_loop+6>
xpsr 0x81000000 -2130706432
fpscr 0x0 0
msp 0x2404ffe0 0x2404ffe0
psp 0x24002e90 0x24002e90 <ucHeap+3088> <== SHOULD BE &pxQueue->uxItemSize!!!
primask 0x0 0
basepri 0x0 0
faultmask 0x0 0
control 0x2 2So, psp is now pointing to an address inside a mutex. This shouldn't happen :)
and for reference we're in the "tcpip_thread", with
p pxCurrentTCB->pxTopOfStack
$3 = (volatile StackType_t *) 0x240032bc <ucHeap+4156>
p pxCurrentTCB->pxStack
$4 = (StackType_t *) 0x24002f70 <ucHeap+3312>
So psp is below pxStack. I'm at a loss as to what I should be changing in terms of memory settings, linker files, etc., to get this to work. Suggestion would be greatly appreciated!
My full source is attached.