C - addrinfo - pointers segmentation fault
I'm getting a segmentation fault; I made a weird fix but I'm still worried because I can't figure out what the problem was. Any insight would be amazing! Working "fix" in the last code block!
segmentation fault when trying to bind using target_addrinfo:
struct addrinfo *my_server_res;
struct addrinfo *their_server_res;
int main(int argc, char **argv) {
//........
set_addrinfo();
handle_binding();
}
void set_addrinfo() {
int status;
struct addrinfo hints;
struct addrinfo *target_addrinfo; // fix (1/3): **target_addrinfo
char ipstr[INET6_ADDRSTRLEN];
// THIS IS TRUE, takes my_server_res
// fix(2/3): (l ? &my_server_res : &their_server_res)
target_addrinfo = (l ? my_server_res : their_server_res);
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
char *node;
node = (l ? "localhost" : host_name);
// fix (3/3) 3rd argument: target_addrinfo
if ((status = getaddrinfo(node, port, &hints, &target_addrinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
exit(1);
}
}
void handle_binding() {
struct addrinfo *target_addrinfo;
// THIS IS TRUE, takes my_server_res
target_addrinfo = (l ? my_server_res : their_server_res);
int b_res = bind(sockfd, target_addrinfo->ai_addr, target_addrinfo->ai_addrlen);
if (b_res == -1) {
perror("__Bind");
exit(1);
}
}
stack trace: problem when trying to use my_server_res again?:
Program received signal SIGSEGV, Segmentation fault.
0x0000000000401e16 in handle_binding () at ncTh.c:385
385 int b_res = bind(sockfd, target_addrinfo->ai_addr, target_addrinfo->ai_addrlen);
(gdb) backtrace
#0 0x0000000000401e16 in handle_binding () at ncTh.c:385
#1 0x0000000000401cad in setup_socket () at ncTh.c:330
#2 0x0000000000401ad0 in main (argc=6, argv=0x7fffffffdea8) at ncTh.c:266
(gdb) frame 0
#0 0x0000000000401e16 in handle_binding () at ncTh.c:385
385 int b_res = bind(sockfd, target_addrinfo->ai_addr, target_addrinfo->ai_addrlen);
(gdb)
working "fix", changes to set_addrinfo():
struct addrinfo **target_addrinfo; // was *target_addrinfo
char ipstr[INET6_ADDRSTRLEN];
target_addrinfo = (l ? &my_server_res : &their_server_res); // was my_server_res : their_server_res
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
char *node;
node = (l ? "localhost" : host_name);
// 3rd argument was &target_addrinfo :
if ((status = getaddrinfo(node, port, &hints, target_addrinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
exit(1);
}
In the original code:
struct addrinfo *target_addrinfo;
target_addrinfo = (l ? my_server_res : their_server_res);
This copies the value of the pointer my_server_res
into target_addrinfo
.
getaddrinfo(node, port, &hints, &target_addrinfo)
This passes a pointer to target_addrinfo
(a pointer to a pointer) into the function getaddrinfo
which then assigns a new value to it, by doing the equivalent of *&target_addrinfo = new_ptr
. This new value is a pointer to the information getaddrinfo
is retrieving for you.
All this has no effect on my_server_res
which remains with its original value, likely NULL.
In the new code:
struct addrinfo **target_addrinfo;
target_addrinfo = (l ? &my_server_res : &their_server_res);
This copies a pointer to my_server_res
into target_addrinfo
(which is now a pointer to a pointer).
getaddrinfo(node, port, &hints, target_addrinfo)
This passes the value of target_addrinfo
(which is currently a pointer to my_server_res
) into the function getaddrinfo
which then assigns a new value to it, by doing the equivalent of *target_addrinfo = new_ptr
. my_server_res
now contains a pointer to the information getaddrinfo
is retrieving for you.
you will probably fall in dereferencing of target_addrinfo
problem, i posted this code. (better late then never :))
struct addrinfo *my_server_res;
struct addrinfo *their_server_res;
struct addrinfo **target_addrinfo; //this should be global
int main(int argc, char **argv) {
//........
set_addrinfo();
handle_binding();
}
void set_addrinfo() {
int status;
struct addrinfo hints;
char ipstr[INET6_ADDRSTRLEN];
// THIS IS TRUE, takes my_server_res
target_addrinfo = (l ? &my_server_res : &their_server_res); //set it once here
memset(&hints, 0, sizeof hints);
hints.ai_family = AF_INET;
hints.ai_socktype = SOCK_STREAM;
hints.ai_flags = AI_PASSIVE;
char *node;
node = (l ? "localhost" : host_name);
if ((status = getaddrinfo(node, port, &hints, &target_addrinfo)) != 0) {
fprintf(stderr, "getaddrinfo error: %s\n", gai_strerror(status));
exit(1);
}
}
void handle_binding() {
//target_addrinfo should be initialized in set_addrinfo()
int b_res = bind(sockfd,
(*target_addrinfo)->ai_addr, // don't forget to dereference target_addrinfo, here
(*target_addrinfo)->ai_addrlen); // and here
if (b_res == -1) {
perror("__Bind");
exit(1);
}
}
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