Accessing syscalls from C

This is a discussion on Accessing syscalls from C within the C Programming forums, part of the General Programming Boards category; Hi, I tried to access some syscalls using C but I'm stuck. I found an IBM-paper telling that the _syscallN() ...

  1. #1
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    Accessing syscalls from C

    Hi,
    I tried to access some syscalls using C but I'm stuck. I found an IBM-paper telling that the _syscallN() macros can be used for this. But I don't have these macros. Now someone told me that they would be obsolete on newer kernel-version. But how can I than access the syscalls from C ?

    PS: Without inline assembly if possible.
    Last edited by lilcoder; 09-07-2007 at 09:43 AM. Reason: added PS

  2. #2
    and the hat of wrongness Salem's Avatar
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    This seems horribly specific to the Operating system and compiler you're using at the moment.

    What are you using?
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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  3. #3
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    Hi Salem,
    • my kernel: 2.6.20-16-386
    • my compilersuite: gcc (GCC) 4.1.2 (Ubuntu 4.1.2-0ubuntu4)


    bye

  4. #4
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    Well, since the IBM paper is talking about Linux, I'll presume that the original poster is using Linux too.

    I'm pretty sure those macros are in <sys/syscall.h> - if you don't have that file, you may need to install something like a "Kernel headers" package, perhaps.

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    Please don't PM me for help - and no, I don't do help over instant messengers.

  5. #5
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    Well in the IBM-paper is written:
    The _syscallN macros are defined in /usr/include/linux/unistd.h and have the following format:

    _syscall0( ret-type, func-name )
    _syscall1( ret-type, func-name, arg1-type, arg1-name )
    _syscall2( ret-type, func-name, arg1-type, arg1-name, arg2-type, arg2-name )
    but they are not defined in unistd.h here. In syscall.h they are also not:
    Code:
    $ cat /usr/include/sys/syscall.h
    /* Copyright (C) 1995, 1996, 1997 Free Software Foundation, Inc.
       This file is part of the GNU C Library.
    
       The GNU C Library is free software; you can redistribute it and/or
       modify it under the terms of the GNU Lesser General Public
       License as published by the Free Software Foundation; either
       version 2.1 of the License, or (at your option) any later version.
    
       The GNU C Library is distributed in the hope that it will be useful,
       but WITHOUT ANY WARRANTY; without even the implied warranty of
       MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
       Lesser General Public License for more details.
    
       You should have received a copy of the GNU Lesser General Public
       License along with the GNU C Library; if not, write to the Free
       Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
       02111-1307 USA.  */
    
    #ifndef _SYSCALL_H
    #define _SYSCALL_H      1
    
    /* This file should list the numbers of the system the system knows.
       But instead of duplicating this we use the information available
       from the kernel sources.  */
    #include <asm/unistd.h>
    
    #ifndef _LIBC
    /* The Linux kernel header file defines macros `__NR_<name>', but some
       programs expect the traditional form `SYS_<name>'.  So in building libc
       we scan the kernel's list and produce <bits/syscall.h> with macros for
       all the `SYS_' names.  */
    # include <bits/syscall.h>
    #endif
    
    #endif
    And as said I was told they would have become obsolete on newer kernels but I couldn't find an other methode to access them.

  6. #6
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    Obsolete? Why? 2.6.20 that the document talks about is only a few months old, and you are using 2.6.20 anyways, so I don't see how it could be obsolete - no matter what, you do NEED system calls, and including <sys/syscalls.h> should achieve that, but it may well be inside the <bits/syscalls.h> or some include file further down the tree.

    I'm not entirely sure what you expect to achieve by this, but that's beside the point.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  7. #7
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    i found it by following the includes.
    #include <asm/unistd.h>

  8. #8
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    Hi,
    Code:
    $ cat /usr/include/linux/unistd.h
    #ifndef _LINUX_UNISTD_H_
    #define _LINUX_UNISTD_H_
    
    /*
     * Include machine specific syscall numbers
     */
    #include <asm/unistd.h>
    
    #endif /* _LINUX_UNISTD_H_ */
    
    $cat /usr/include/asm/unistd.h
    /* File autogenerated by 'make headers_install' */
    #ifndef __ASM_STUB_UNISTD_H
    #define __ASM_STUB_UNISTD_H
    # if defined __x86_64__
    #  include <asm-x86_64/unistd.h>
    # elif defined __i386__
    #  include <asm-i386/unistd.h>
    # else
    #  warning This machine appears to be neither x86_64 nor i386.
    # endif
    #endif /* __ASM_STUB_UNISTD_H */
    and /usr/include/asm-i386/unistd.h just contains the syscall numbers like:
    Code:
    #define __NR_restart_syscall      0
    #define __NR_exit                 1
    #define __NR_fork                 2
    #define __NR_read                 3
    #define __NR_write                4
    [...]
    But no _syscallN macros? Can it be that my distribution (Ubuntu) is not supporting them?

  9. #9
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    Quote Originally Posted by lilcoder View Post
    Hi,
    I tried to access some syscalls using C but I'm stuck. I found an IBM-paper telling that the _syscallN() macros can be used for this. But I don't have these macros. Now someone told me that they would be obsolete on newer kernel-version. But how can I than access the syscalls from C ?

    PS: Without inline assembly if possible.
    Is there some reason you don't want to call them through the C library?

  10. #10
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    Quote Originally Posted by lilcoder View Post
    But no _syscallN macros? Can it be that my distribution (Ubuntu) is not supporting them?
    do a find (Ctrl-F) for syscall. NR macros are just listed first.

  11. #11
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    No they are not here:
    Code:
     cat /usr/include/asm-i386/unistd.h
    #ifndef _ASM_I386_UNISTD_H_
    #define _ASM_I386_UNISTD_H_
    
    /*
     * This file contains the system call numbers.
     */
    
    #define __NR_restart_syscall      0
    #define __NR_exit                 1
    #define __NR_fork                 2
    #define __NR_read                 3
    #define __NR_write                4
    #define __NR_open                 5
    #define __NR_close                6
    #define __NR_waitpid              7
    #define __NR_creat                8
    #define __NR_link                 9
    #define __NR_unlink              10
    #define __NR_execve              11
    #define __NR_chdir               12
    #define __NR_time                13
    #define __NR_mknod               14
    #define __NR_chmod               15
    #define __NR_lchown              16
    #define __NR_break               17
    #define __NR_oldstat             18
    #define __NR_lseek               19
    #define __NR_getpid              20
    #define __NR_mount               21
    #define __NR_umount              22
    #define __NR_setuid              23
    #define __NR_getuid              24
    #define __NR_stime               25
    #define __NR_ptrace              26
    #define __NR_alarm               27
    #define __NR_oldfstat            28
    #define __NR_pause               29
    #define __NR_utime               30
    #define __NR_stty                31
    #define __NR_gtty                32
    #define __NR_access              33
    #define __NR_nice                34
    #define __NR_ftime               35
    #define __NR_sync                36
    #define __NR_kill                37
    #define __NR_rename              38
    #define __NR_mkdir               39
    #define __NR_rmdir               40
    #define __NR_dup                 41
    #define __NR_pipe                42
    #define __NR_times               43
    #define __NR_prof                44
    #define __NR_brk                 45
    #define __NR_setgid              46
    #define __NR_getgid              47
    #define __NR_signal              48
    #define __NR_geteuid             49
    #define __NR_getegid             50
    #define __NR_acct                51
    #define __NR_umount2             52
    #define __NR_lock                53
    #define __NR_ioctl               54
    #define __NR_fcntl               55
    #define __NR_mpx                 56
    #define __NR_setpgid             57
    #define __NR_ulimit              58
    #define __NR_oldolduname         59
    #define __NR_umask               60
    #define __NR_chroot              61
    #define __NR_ustat               62
    #define __NR_dup2                63
    #define __NR_getppid             64
    #define __NR_getpgrp             65
    #define __NR_setsid              66
    #define __NR_sigaction           67
    #define __NR_sgetmask            68
    #define __NR_ssetmask            69
    #define __NR_setreuid            70
    #define __NR_setregid            71
    #define __NR_sigsuspend          72
    #define __NR_sigpending          73
    #define __NR_sethostname         74
    #define __NR_setrlimit           75
    #define __NR_getrlimit           76     /* Back compatible 2Gig limited rlimit */
    #define __NR_getrusage           77
    #define __NR_gettimeofday        78
    #define __NR_settimeofday        79
    #define __NR_getgroups           80
    #define __NR_setgroups           81
    #define __NR_select              82
    #define __NR_symlink             83
    #define __NR_oldlstat            84
    #define __NR_readlink            85
    #define __NR_uselib              86
    #define __NR_swapon              87
    #define __NR_reboot              88
    #define __NR_readdir             89
    #define __NR_mmap                90
    #define __NR_munmap              91
    #define __NR_truncate            92
    #define __NR_ftruncate           93
    #define __NR_fchmod              94
    #define __NR_fchown              95
    #define __NR_getpriority         96
    #define __NR_setpriority         97
    #define __NR_profil              98
    #define __NR_statfs              99
    #define __NR_fstatfs            100
    #define __NR_ioperm             101
    #define __NR_socketcall         102
    #define __NR_syslog             103
    #define __NR_setitimer          104
    #define __NR_getitimer          105
    #define __NR_stat               106
    #define __NR_lstat              107
    #define __NR_fstat              108
    #define __NR_olduname           109
    #define __NR_iopl               110
    #define __NR_vhangup            111
    #define __NR_idle               112
    #define __NR_vm86old            113
    #define __NR_wait4              114
    #define __NR_swapoff            115
    #define __NR_sysinfo            116
    #define __NR_ipc                117
    #define __NR_fsync              118
    #define __NR_sigreturn          119
    #define __NR_clone              120
    #define __NR_setdomainname      121
    #define __NR_uname              122
    #define __NR_modify_ldt         123
    #define __NR_adjtimex           124
    #define __NR_mprotect           125
    #define __NR_sigprocmask        126
    #define __NR_create_module      127
    #define __NR_init_module        128
    #define __NR_delete_module      129
    #define __NR_get_kernel_syms    130
    #define __NR_quotactl           131
    #define __NR_getpgid            132
    #define __NR_fchdir             133
    #define __NR_bdflush            134
    #define __NR_sysfs              135
    #define __NR_personality        136
    #define __NR_afs_syscall        137 /* Syscall for Andrew File System */
    #define __NR_setfsuid           138
    #define __NR_setfsgid           139
    #define __NR__llseek            140
    #define __NR_getdents           141
    #define __NR__newselect         142
    #define __NR_flock              143
    #define __NR_msync              144
    #define __NR_readv              145
    #define __NR_writev             146
    #define __NR_getsid             147
    #define __NR_fdatasync          148
    #define __NR__sysctl            149
    #define __NR_mlock              150
    #define __NR_munlock            151
    #define __NR_mlockall           152
    #define __NR_munlockall         153
    #define __NR_sched_setparam             154
    #define __NR_sched_getparam             155
    #define __NR_sched_setscheduler         156
    #define __NR_sched_getscheduler         157
    #define __NR_sched_yield                158
    #define __NR_sched_get_priority_max     159
    #define __NR_sched_get_priority_min     160
    #define __NR_sched_rr_get_interval      161
    #define __NR_nanosleep          162
    #define __NR_mremap             163
    #define __NR_setresuid          164
    #define __NR_getresuid          165
    #define __NR_vm86               166
    #define __NR_query_module       167
    #define __NR_poll               168
    #define __NR_nfsservctl         169
    #define __NR_setresgid          170
    #define __NR_getresgid          171
    #define __NR_prctl              172
    #define __NR_rt_sigreturn       173
    #define __NR_rt_sigaction       174
    #define __NR_rt_sigprocmask     175
    #define __NR_rt_sigpending      176
    #define __NR_rt_sigtimedwait    177
    #define __NR_rt_sigqueueinfo    178
    #define __NR_rt_sigsuspend      179
    #define __NR_pread64            180
    #define __NR_pwrite64           181
    #define __NR_chown              182
    #define __NR_getcwd             183
    #define __NR_capget             184
    #define __NR_capset             185
    #define __NR_sigaltstack        186
    #define __NR_sendfile           187
    #define __NR_getpmsg            188     /* some people actually want streams */
    #define __NR_putpmsg            189     /* some people actually want streams */
    #define __NR_vfork              190
    #define __NR_ugetrlimit         191     /* SuS compliant getrlimit */
    #define __NR_mmap2              192
    #define __NR_truncate64         193
    #define __NR_ftruncate64        194
    #define __NR_stat64             195
    #define __NR_lstat64            196
    #define __NR_fstat64            197
    #define __NR_lchown32           198
    #define __NR_getuid32           199
    #define __NR_getgid32           200
    #define __NR_geteuid32          201
    #define __NR_getegid32          202
    #define __NR_setreuid32         203
    #define __NR_setregid32         204
    #define __NR_getgroups32        205
    #define __NR_setgroups32        206
    #define __NR_fchown32           207
    #define __NR_setresuid32        208
    #define __NR_getresuid32        209
    #define __NR_setresgid32        210
    #define __NR_getresgid32        211
    #define __NR_chown32            212
    #define __NR_setuid32           213
    #define __NR_setgid32           214
    #define __NR_setfsuid32         215
    #define __NR_setfsgid32         216
    #define __NR_pivot_root         217
    #define __NR_mincore            218
    #define __NR_madvise            219
    #define __NR_madvise1           219     /* delete when C lib stub is removed */
    #define __NR_getdents64         220
    #define __NR_fcntl64            221
    /* 223 is unused */
    #define __NR_gettid             224
    #define __NR_readahead          225
    #define __NR_setxattr           226
    #define __NR_lsetxattr          227
    #define __NR_fsetxattr          228
    #define __NR_getxattr           229
    #define __NR_lgetxattr          230
    #define __NR_fgetxattr          231
    #define __NR_listxattr          232
    #define __NR_llistxattr         233
    #define __NR_flistxattr         234
    #define __NR_removexattr        235
    #define __NR_lremovexattr       236
    #define __NR_fremovexattr       237
    #define __NR_tkill              238
    #define __NR_sendfile64         239
    #define __NR_futex              240
    #define __NR_sched_setaffinity  241
    #define __NR_sched_getaffinity  242
    #define __NR_set_thread_area    243
    #define __NR_get_thread_area    244
    #define __NR_io_setup           245
    #define __NR_io_destroy         246
    #define __NR_io_getevents       247
    #define __NR_io_submit          248
    #define __NR_io_cancel          249
    #define __NR_fadvise64          250
    /* 251 is available for reuse (was briefly sys_set_zone_reclaim) */
    #define __NR_exit_group         252
    #define __NR_lookup_dcookie     253
    #define __NR_epoll_create       254
    #define __NR_epoll_ctl          255
    #define __NR_epoll_wait         256
    #define __NR_remap_file_pages   257
    #define __NR_set_tid_address    258
    #define __NR_timer_create       259
    #define __NR_timer_settime      (__NR_timer_create+1)
    #define __NR_timer_gettime      (__NR_timer_create+2)
    #define __NR_timer_getoverrun   (__NR_timer_create+3)
    #define __NR_timer_delete       (__NR_timer_create+4)
    #define __NR_clock_settime      (__NR_timer_create+5)
    #define __NR_clock_gettime      (__NR_timer_create+6)
    #define __NR_clock_getres       (__NR_timer_create+7)
    #define __NR_clock_nanosleep    (__NR_timer_create+8)
    #define __NR_statfs64           268
    #define __NR_fstatfs64          269
    #define __NR_tgkill             270
    #define __NR_utimes             271
    #define __NR_fadvise64_64       272
    #define __NR_vserver            273
    #define __NR_mbind              274
    #define __NR_get_mempolicy      275
    #define __NR_set_mempolicy      276
    #define __NR_mq_open            277
    #define __NR_mq_unlink          (__NR_mq_open+1)
    #define __NR_mq_timedsend       (__NR_mq_open+2)
    #define __NR_mq_timedreceive    (__NR_mq_open+3)
    #define __NR_mq_notify          (__NR_mq_open+4)
    #define __NR_mq_getsetattr      (__NR_mq_open+5)
    #define __NR_kexec_load         283
    #define __NR_waitid             284
    /* #define __NR_sys_setaltroot  285 */
    #define __NR_add_key            286
    #define __NR_request_key        287
    #define __NR_keyctl             288
    #define __NR_ioprio_set         289
    #define __NR_ioprio_get         290
    #define __NR_inotify_init       291
    #define __NR_inotify_add_watch  292
    #define __NR_inotify_rm_watch   293
    #define __NR_migrate_pages      294
    #define __NR_openat             295
    #define __NR_mkdirat            296
    #define __NR_mknodat            297
    #define __NR_fchownat           298
    #define __NR_futimesat          299
    #define __NR_fstatat64          300
    #define __NR_unlinkat           301
    #define __NR_renameat           302
    #define __NR_linkat             303
    #define __NR_symlinkat          304
    #define __NR_readlinkat         305
    #define __NR_fchmodat           306
    #define __NR_faccessat          307
    #define __NR_pselect6           308
    #define __NR_ppoll              309
    #define __NR_unshare            310
    #define __NR_set_robust_list    311
    #define __NR_get_robust_list    312
    #define __NR_splice             313
    #define __NR_sync_file_range    314
    #define __NR_tee                315
    #define __NR_vmsplice           316
    #define __NR_move_pages         317
    #define __NR_getcpu             318
    #define __NR_epoll_pwait        319
    
    #endif /* _ASM_I386_UNISTD_H_ */
    Any idea?

  12. #12
    Woof, woof! zacs7's Avatar
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    I don't think they asked you to post the entire header... rather look for it yourself.

    Why not just search in the files? (All files in /usr/include/ or something), do a man find and man grep and whack something together, like:

    Code:
    find /usr/include | xargs grep 'blah'
    Last edited by zacs7; 09-10-2007 at 12:32 AM.

  13. #13
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    Quote Originally Posted by zacs7 View Post
    I don't think they asked you to post the entire header... rather look for it yourself.
    lol I know how to use grep... I just posted the whole file in order not to get answers telling me to look closer, or I overlooked them. They are not here.

    Really noone any idea?

  14. #14
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    nope, no idea. maybe try a linux forum?

  15. #15
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    Could you point me to a good linux coding forum for advaced topics?

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