当我发现系统调用或Bust 章节中列出了getaddrinfo()时，我正在阅读http://beej.us/guide/bgnet/output/html/singlepage/bgnet.html#syscalls。
我想检查它是否真的是我的Debian 8 Linux系统上的系统调用。但我找不到任何证据表明它是系统调用。
例如，我写了一个程序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;
}
当我使用strace编译并运行此程序时，我看不到对getaddrinfo()的任何调用。
$ 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 +++
我在getaddrinfo()中没有看到man syscalls。
$ man syscalls | grep getaddrinfo
$
那么我可以得出结论getaddrinfo()不是我的Debian Linux系统上的系统调用吗？
在给定的Unix或Linux系统上，是否有更好的方法可以明确地确定给定的函数是否是系统调用？
答案 0 :(得分：3)
不，不是。你的调查证明了这一点。
此外，您可以尝试在Linux syscalls table中找到它。或者打开man page查看它是哪一章：2 - 系统调用; 3 - c函数。