can print from command line, but cannot get it from the program - gdb

Question

I use gdb to debug my program, when I unpack a message and wanna print it, I got a problem. It seems that i can print from command line in the terminal, but when program goes to the printf("%d has received msg: ", msg->connid);, I got the problem,
Program received signal SIGSEGV, Segmentation fault.
0xb7ff6301 in ?? () from /lib/ld-linux.so.2
(gdb)n
154 LSPMessage* msg = lspmessage__unpack(NULL, msg_len, buf);
(gdb) n
156 memcpy(pld, msg->payload.data, msg->payload.len);
(gdb) p msg->payload.data
$1 = (uint8_t *) 0x804c038 "Connectedrt,\031"
(gdb) p msg->connid
$2 = 1
(gdb) p msg->payload.len
$3 = 9
174 printf("%d has received msg: ", msg->connid); // required field
(gdb) n
Program received signal SIGSEGV, Segmentation fault.
0xb7ff6301 in ?? () from /lib/ld-linux.so.2

Answer 1

You did a remarkably poor job of explaining what it is you are actually asking.
I think your question is: "how come my printf call crashes?".
There could be several reasons
You have corrupted stdout earlier, or
msg->connid is not int (and so it is wrong to printf it with "%d", or
you have corrupted something else in the runtime loader state, and it now crashes while doing lazy PLT symbol resolution
Since you crash is inside the runtime loader, that last cause appears to be most likely. You can confirm this hypothesis by forcing the loader to perform symol resolution non-lazily:
(gdb) set env LD_BIND_NOW 1
(gdb) run
Did it still crash? If not, run your program under Valgrind, and be sure to fix all the problems it reports.