SIGSEGV at somewhere should not be, there's no NULL pointer - c

Question

I use gdb test core and get this:
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x0000557ce64b63f8 in _create (str=str#entry=0x557ce80a8820 "SEND")
at system.c:708
708 data->res = command->data->res;
(gdb) bt
#0 0x0000557ce64b63f8 in _create (str=str#entry=0x557ce80a8820 "SEND")
at system.c:708
#1 0x0000557ce64b2ef1 in make_command (s=<optimized out>, cmd=0x557ce809cb70) at command.c:121
#2 0x0000557ce63aefdf in main (argc=<optimized out>, argv=0x7fff19053278) at main.c:394
(gdb) p *command
$1 = {status = 1, data = 0x7f21027e9a80, sum = 1543465568, time = 0, msg = { str = 0x7f20fd19f080 "GOOD", len = 4}, id = 2}
(gdb) p *command->data
$2 = {status = 1, item = 0x7f21027eb780, res = 0x7f2100990b00, sum = 1133793665}
(gdb) p *command->data->res
$3 = {msg = { str = 0x7f21010a5500 "Hi, test, test"..., len = 14}, status = 1}
(gdb) p *data
$4 = {status = 1, type = 5, res = 0x0, id = 2}
as you can see, the pointer command and command->data and data are all valid, why this SIGSEGV happened?

Answer 1

why this SIGSEGV happened?
We can't tell.
One possible reason: some other code is actually executing and crashing.
This could happen if system.c has been edited or updated, but the program has not been rebuilt with the new source. Or if the compiler mapping of program counter to file/line is inaccurate (this often happens with optimized code).
If you edit your question to show the output from list _create, disas $pc and info registers, we may be able to tell you more.