sysdeps/unix/syscall-template.S

   1 /* Assembly code template for system call stubs.
   2    Copyright (C) 2009-2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 /* The real guts of this work are in the macros defined in the
  20    machine- and kernel-specific sysdep.h header file.  When we
  21    are defining a cancellable system call, the sysdep-cancel.h
  22    versions of those macros are what we really use.
  23
  24    Each system call's object is built by a rule in sysd-syscalls
  25    generated by make-syscalls.sh that #include's this file after
  26    defining a few macros:
  27         SYSCALL_NAME            syscall name
  28         SYSCALL_NARGS           number of arguments this call takes
  29         SYSCALL_SYMBOL          primary symbol name
  30         SYSCALL_CANCELLABLE     1 if the call is a cancelation point
  31         SYSCALL_NOERRNO         1 to define a no-errno version (see below)
  32         SYSCALL_ERRVAL          1 to define an error-value version (see below)
  33
  34    We used to simply pipe the correct three lines below through cpp into
  35    the assembler.  The main reason to have this file instead is so that
  36    stub objects can be assembled with -g and get source line information
  37    that leads a user back to a source file and these fine comments.  The
  38    average user otherwise has a hard time knowing which "syscall-like"
  39    functions in libc are plain stubs and which have nontrivial C wrappers.
  40    Some versions of the "plain" stub generation macros are more than a few
  41    instructions long and the untrained eye might not distinguish them from
  42    some compiled code that inexplicably lacks source line information.  */
  43
  44 #if SYSCALL_CANCELLABLE
  45 # include <sysdep-cancel.h>
  46 #else
  47 # include <sysdep.h>
  48 #endif
  49
  50 #define T_PSEUDO(SYMBOL, NAME, N)               PSEUDO (SYMBOL, NAME, N)
  51 #define T_PSEUDO_NOERRNO(SYMBOL, NAME, N)       PSEUDO_NOERRNO (SYMBOL, NAME, N)
  52 #define T_PSEUDO_ERRVAL(SYMBOL, NAME, N)        PSEUDO_ERRVAL (SYMBOL, NAME, N)
  53 #define T_PSEUDO_END(SYMBOL)                    PSEUDO_END (SYMBOL)
  54 #define T_PSEUDO_END_NOERRNO(SYMBOL)            PSEUDO_END_NOERRNO (SYMBOL)
  55 #define T_PSEUDO_END_ERRVAL(SYMBOL)             PSEUDO_END_ERRVAL (SYMBOL)
  56
  57 #if SYSCALL_NOERRNO
  58
  59 /* This kind of system call stub never returns an error.
  60    We return the return value register to the caller unexamined.  */
  61
  62 T_PSEUDO_NOERRNO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
  63         ret_NOERRNO
  64 T_PSEUDO_END_NOERRNO (SYSCALL_SYMBOL)
  65
  66 #elif SYSCALL_ERRVAL
  67
  68 /* This kind of system call stub returns the errno code as its return
  69    value, or zero for success.  We may massage the kernel's return value
  70    to meet that ABI, but we never set errno here.  */
  71
  72 T_PSEUDO_ERRVAL (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
  73         ret_ERRVAL
  74 T_PSEUDO_END_ERRVAL (SYSCALL_SYMBOL)
  75
  76 #else
  77
  78 /* This is a "normal" system call stub: if there is an error,
  79    it returns -1 and sets errno.  */
  80
  81 T_PSEUDO (SYSCALL_SYMBOL, SYSCALL_NAME, SYSCALL_NARGS)
  82         ret
  83 T_PSEUDO_END (SYSCALL_SYMBOL)
  84
  85 #endif
  86
  87 libc_hidden_def (SYSCALL_SYMBOL)