I was reading http://beej.us/guide/bgnet/output/html/singlepage/bgnet.html#syscalls when I found that getaddrinfo() is listed under the System Calls or Bust chapter.
I wanted to check if it really is a system call on my Debian 8 Linux system. But I can't find any evidence of it being a system call.
For example, I wrote a program foo.c.
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
int main()
{
struct addrinfo *ai;
int ret;
ret = getaddrinfo("localhost", "http", NULL, &ai);
printf("ret: %d\n", ret);
return 0;
}
When I compile and run this program with strace, I don't see any call to getaddrinfo().
$ gcc foo.c && strace ./a.out
execve("./a.out", ["./a.out"], [/* 40 vars */]) = 0
brk(0) = 0x1190000
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a59000
access("/etc/ld.so.preload", R_OK) = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=76177, ...}) = 0
mmap(NULL, 76177, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f99f5a46000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\34\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1738176, ...}) = 0
mmap(NULL, 3844640, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f99f5490000
mprotect(0x7f99f5632000, 2093056, PROT_NONE) = 0
mmap(0x7f99f5831000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1a1000) = 0x7f99f5831000
mmap(0x7f99f5837000, 14880, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7f99f5837000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a45000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a44000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a43000
arch_prctl(ARCH_SET_FS, 0x7f99f5a44700) = 0
mprotect(0x7f99f5831000, 16384, PROT_READ) = 0
mprotect(0x7f99f5a5b000, 4096, PROT_READ) = 0
munmap(0x7f99f5a46000, 76177) = 0
socket(PF_NETLINK, SOCK_RAW, NETLINK_ROUTE) = 3
bind(3, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 0
getsockname(3, {sa_family=AF_NETLINK, pid=24206, groups=00000000}, [12]) = 0
sendto(3, "\24\0\0\0\26\0\1\3c\350DX\0\0\0\0\0\0\0\0", 20, 0, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 20
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"L\0\0\0\24\0\2\0c\350DX\216^\0\0\2\10\200\376\1\0\0\0\10\0\1\0\177\0\0\1"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 252
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"H\0\0\0\24\0\2\0c\350DX\216^\0\0\n\200\200\376\1\0\0\0\24\0\1\0\0\0\0\0"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 216
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"\24\0\0\0\3\0\2\0c\350DX\216^\0\0\0\0\0\0", 4096}], msg_controllen=0, msg_flags=0}, 0) = 20
brk(0) = 0x1190000
brk(0x11b1000) = 0x11b1000
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
connect(4, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(4) = 0
close(3) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3) = 0
open("/etc/nsswitch.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=529, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# /etc/nsswitch.conf\n#\n# Example"..., 4096) = 529
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=76177, ...}) = 0
mmap(NULL, 76177, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f99f5a46000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu/tls/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu/tls", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64-linux-gnu", {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0
open("/usr/lib/x86_64-linux-gnu/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/tls/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/tls", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64-linux-gnu/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64-linux-gnu", {st_mode=S_IFDIR|0755, st_size=49152, ...}) = 0
open("/lib/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/tls/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/lib/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/tls", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/lib/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/lib/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/lib", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/usr/lib/tls/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/usr/lib/tls/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/tls", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/usr/lib/x86_64/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib/x86_64", 0x7ffee66a14d0) = -1 ENOENT (No such file or directory)
open("/usr/lib/libnss_db.so.2", O_RDONLY|O_CLOEXEC) = -1 ENOENT (No such file or directory)
stat("/usr/lib", {st_mode=S_IFDIR|0755, st_size=12288, ...}) = 0
munmap(0x7f99f5a46000, 76177) = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=76177, ...}) = 0
mmap(NULL, 76177, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7f99f5a46000
close(3) = 0
access("/etc/ld.so.nohwcap", F_OK) = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libnss_files.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240\"\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0644, st_size=47712, ...}) = 0
mmap(NULL, 2144392, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7f99f5284000
mprotect(0x7f99f528f000, 2093056, PROT_NONE) = 0
mmap(0x7f99f548e000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xa000) = 0x7f99f548e000
close(3) = 0
mprotect(0x7f99f548e000, 4096, PROT_READ) = 0
munmap(0x7f99f5a46000, 76177) = 0
open("/etc/services", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=19605, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Network services, Internet sty"..., 4096) = 4096
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/services", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=19605, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Network services, Internet sty"..., 4096) = 4096
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/services", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=19605, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Network services, Internet sty"..., 4096) = 4096
read(3, "\t\t# IPX\nipx\t\t213/udp\nimap3\t\t220/"..., 4096) = 4096
read(3, "nessus\t\t1241/tcp\t\t\t# Nessus vuln"..., 4096) = 4096
read(3, "347/tcp\t\t\t# gnutella\ngnutella-rt"..., 4096) = 4096
read(3, "ureg\t779/udp\t\tmoira_ureg\t# Moira"..., 4096) = 3221
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/services", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=19605, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Network services, Internet sty"..., 4096) = 4096
read(3, "\t\t# IPX\nipx\t\t213/udp\nimap3\t\t220/"..., 4096) = 4096
read(3, "nessus\t\t1241/tcp\t\t\t# Nessus vuln"..., 4096) = 4096
read(3, "347/tcp\t\t\t# gnutella\ngnutella-rt"..., 4096) = 4096
read(3, "ureg\t779/udp\t\tmoira_ureg\t# Moira"..., 4096) = 3221
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/services", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=19605, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Network services, Internet sty"..., 4096) = 4096
read(3, "\t\t# IPX\nipx\t\t213/udp\nimap3\t\t220/"..., 4096) = 4096
read(3, "nessus\t\t1241/tcp\t\t\t# Nessus vuln"..., 4096) = 4096
read(3, "347/tcp\t\t\t# gnutella\ngnutella-rt"..., 4096) = 4096
read(3, "ureg\t779/udp\t\tmoira_ureg\t# Moira"..., 4096) = 3221
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/services", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=19605, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Network services, Internet sty"..., 4096) = 4096
read(3, "\t\t# IPX\nipx\t\t213/udp\nimap3\t\t220/"..., 4096) = 4096
read(3, "nessus\t\t1241/tcp\t\t\t# Nessus vuln"..., 4096) = 4096
read(3, "347/tcp\t\t\t# gnutella\ngnutella-rt"..., 4096) = 4096
read(3, "ureg\t779/udp\t\tmoira_ureg\t# Moira"..., 4096) = 3221
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
socket(PF_LOCAL, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_LOCAL, sun_path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3) = 0
open("/etc/host.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=9, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "multi on\n", 4096) = 9
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
getpid() = 24206
open("/etc/resolv.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=124, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Generated by NetworkManager\nse"..., 4096) = 124
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=207, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "127.0.0.1\tlocalhost\n127.0.1.1\tde"..., 4096) = 207
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
open("/etc/gai.conf", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=2584, ...}) = 0
fstat(3, {st_mode=S_IFREG|0644, st_size=2584, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
read(3, "# Configuration for getaddrinfo("..., 4096) = 2584
read(3, "", 4096) = 0
close(3) = 0
munmap(0x7f99f5a58000, 4096) = 0
socket(PF_INET, SOCK_DGRAM, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(80), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
getsockname(3, {sa_family=AF_INET, sin_port=htons(60650), sin_addr=inet_addr("127.0.0.1")}, [16]) = 0
close(3) = 0
socket(PF_INET6, SOCK_DGRAM, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET6, sin6_port=htons(80), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, 28) = 0
getsockname(3, {sa_family=AF_INET6, sin6_port=htons(51869), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=0, sin6_scope_id=0}, [28]) = 0
close(3) = 0
fstat(1, {st_mode=S_IFREG|0644, st_size=13847, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f99f5a58000
write(1, "ret: 0\n", 7ret: 0
) = 7
exit_group(0) = ?
+++ exited with 0 +++
I don't see getaddrinfo() mentioned in man syscalls.
$ man syscalls | grep getaddrinfo
$
So can I conclude that getaddrinfo() is not a system call on my Debian Linux system?
Is there a better way to definitevely determine if a given function is a system call or not on a given Unix or Linux system?
No, it is not. Your investigation proves it.
Additionally, you can try to find it in the Linux syscalls table. Or open man page for it check which chapter it is: 2 - system calls; 3 - c functions.