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           #define _GNU_SOURCE         /* See feature_test_macros(7) */
           #include <unistd.h>
           #include <sys/syscall.h>   /* For SYS_xxx definitions */
           int syscall(int number, ...);


           syscall()  is  a  small  library  function that invokes the system call
           whose assembly language interface has the  specified  number  with  the
           specified  arguments.  Employing syscall() is useful, for example, when
           invoking a system call that has no wrapper function in the C library.
           syscall() saves CPU registers before making the system  call,  restores
           the  registers  upon  return from the system call, and stores any error
           code returned by the system call in errno(3) if an error occurs.
           Symbolic constants for system call numbers can be found in  the  header
           file <sys/syscall.h>.


           The  return value is defined by the system call being invoked.  In gen-
           eral, a 0 return value indicates success.  A -1 return value  indicates
           an error, and an error code is stored in errno.


           syscall() first appeared in 4BSD.
       Architecture-specific requirements
           Each architecture ABI has its own requirements on how system call argu-
           ments are passed to the kernel.  For system calls  that  have  a  glibc
           wrapper (e.g., most system calls), glibc handles the details of copying
           arguments to the right registers in a manner suitable for the architec-
           ture.   However, when using syscall() to make a system call, the caller
           might need to handle architecture-dependent details;  this  requirement
           is most commonly encountered on certain 32-bit architectures.
           For  example,  on  the  ARM  architecture Embedded ABI (EABI), a 64-bit
           value (e.g., long long) must be  aligned  to  an  even  register  pair.
           Thus,  using  syscall()  instead  of the wrapper provided by glibc, the
           readahead() system call would be invoked as follows on the  ARM  archi-
           tecture with the EABI:
               syscall(SYS_readahead, fd, 0,
                       (unsigned int) (offset >> 32),
                       (unsigned int) (offset & 0xFFFFFFFF),
           Since  the  offset  argument is 64 bits, and the first argument (fd) is
           passed in r0, the caller must manually split and align the 64-bit value
           so  that it is passed in the r2/r3 register pair.  That means inserting
           a dummy value into r1 (the second argument of 0).
           mode, (which might not be the fastest or best way to transition to  the
           kernel,  so  you  might have to refer to vdso(7)), the register used to
           indicate the system call number, and the register used  to  return  the
           system call result.
           arch/ABI   instruction          syscall #   retval Notes
           arm/OABI   swi NR               -           a1     NR is syscall #
           arm/EABI   swi 0x0              r7          r0
           blackfin   excpt 0x0            P0          R0
           i386       int $0x80            eax         eax
           ia64       break 0x100000       r15         r10/r8 bool error/
                                                              errno value
           parisc     ble 0x100(%sr2, %r0) r20         r28
           s390       svc 0                r1          r2     See below
           s390x      svc 0                r1          r2     See below
           sparc/32   t 0x10               g1          o0
           sparc/64   t 0x6d               g1          o0
           x86_64     syscall              rax         rax
           For  s390 and s390x, NR (the system call number) may be passed directly
           with "svc NR" if it is less than 256.
           The second table shows the registers used to pass the system call argu-
           arch/ABI   arg1   arg2   arg3   arg4   arg5   arg6   arg7
           arm/OABI   a1     a2     a3     a4     v1     v2     v3
           arm/EABI   r0     r1     r2     r3     r4     r5     r6
           blackfin   R0     R1     R2     R3     R4     R5     -
           i386       ebx    ecx    edx    esi    edi    ebp    -
           ia64       out0   out1   out2   out3   out4   out5   -
           parisc     r26    r25    r24    r23    r22    r21    -
           s390       r2     r3     r4     r5     r6     r7     -
           s390x      r2     r3     r4     r5     r6     r7     -
           sparc/32   o0     o1     o2     o3     o4     o5     -
           sparc/64   o0     o1     o2     o3     o4     o5     -
           x86_64     rdi    rsi    rdx    r10    r8     r9     -
           Note  that  these tables don't cover the entire calling convention--some
           architectures may indiscriminately clobber other registers  not  listed


           #define _GNU_SOURCE
           #include <unistd.h>
           #include <sys/syscall.h>
           #include <sys/types.h>
           #include <signal.h>

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