sysdeps/unix/sysv/linux/i386/sysdep.h

   1 /* Copyright (C) 1992, 93, 95, 96 Free Software Foundation, Inc.
   2 This file is part of the GNU C Library.
   3 Contributed by Ulrich Drepper, <drepper@gnu.ai.mit.edu>, August 1995.
   4
   5 The GNU C Library is free software; you can redistribute it and/or
   6 modify it under the terms of the GNU Library General Public License as
   7 published by the Free Software Foundation; either version 2 of the
   8 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 Library General Public License for more details.
  14
  15 You should have received a copy of the GNU Library General Public
  16 License along with the GNU C Library; see the file COPYING.LIB.  If
  17 not, write to the Free Software Foundation, Inc., 675 Mass Ave,
  18 Cambridge, MA 02139, USA.  */
  19
  20 #ifndef _LINUX_I386_SYSDEP_H
  21 #define _LINUX_I386_SYSDEP_H 1
  22
  23 /* There is some commonality.  */
  24 #include <sysdeps/unix/i386/sysdep.h>
  25
  26 /* For Linux we can use the system call table in the header file
  27         /usr/include/asm/unistd.h
  28    of the kernel.  But these symbols do not follow the SYS_* syntax
  29    so we have to redefine the `SYS_ify' macro here.  */
  30 #undef SYS_ify
  31 #define SYS_ify(syscall_name)   __NR_##syscall_name
  32
  33
  34 #ifdef ASSEMBLER
  35
  36 /* Linux uses a negative return value to indicate syscall errors,
  37    unlike most Unices, which use the condition codes' carry flag.
  38
  39    Since version 2.1 the return value of a system call might be
  40    negative even if the call succeeded.  E.g., the `lseek' system call
  41    might return a large offset.  Therefore we must not anymore test
  42    for < 0, but test for a real error by making sure the value in %eax
  43    is a real error number.  For now (as of 2.1.1) 122 is the largest
  44    defined error number.  Given a bit room for development, Linus
  45    chose in <asm/unistd.h> to use the values -125 to -1 for error
  46    values.  We follow him here.  */
  47 #undef  PSEUDO
  48 #define PSEUDO(name, syscall_name, args)                                      \
  49   .text;                                                                      \
  50   ENTRY (name)                                                                \
  51     DO_CALL (args, syscall_name);                                             \
  52     cmpl $-125, %eax;                                                         \
  53     jae syscall_error;
  54
  55 #undef  PSEUDO_END
  56 #define PSEUDO_END(name)                                                      \
  57   SYSCALL_ERROR_HANDLER                                                       \
  58   END (name)
  59
  60 #ifndef PIC
  61 #define SYSCALL_ERROR_HANDLER   /* Nothing here; code in sysdep.S is used.  */
  62 #else
  63 /* Store (- %eax) into errno through the GOT.  */
  64 #ifdef _LIBC_REENTRANT
  65 #define SYSCALL_ERROR_HANDLER                                                 \
  66 syscall_error:                                                                \
  67   pushl %ebx;                                                                 \
  68   call 0f;                                                                    \
  69 0:popl %ebx;                                                                  \
  70   xorl %edx, %edx;                                                            \
  71   addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ebx;                                   \
  72   subl %eax, %edx;                                                            \
  73   movl errno@GOT(%ebx), %ecx;                                                 \
  74   movl %edx, (%ecx);                                                          \
  75   pushl %edx;                                                                 \
  76   call __errno_location@PLT;                                                  \
  77   popl %ecx;                                                                  \
  78   popl %ebx;                                                                  \
  79   movl %ecx, (%eax);                                                          \
  80   movl $-1, %eax;                                                             \
  81   ret;
  82 /* A quick note: it is assumed that the call to `__errno_location' does
  83    not modify the stack!  */
  84 #else
  85 #define SYSCALL_ERROR_HANDLER                                                 \
  86 syscall_error:                                                                \
  87   call 0f;                                                                    \
  88 0:popl %ecx;                                                                  \
  89   xorl %edx, %edx;                                                            \
  90   addl $_GLOBAL_OFFSET_TABLE_+[.-0b], %ecx;                                   \
  91   subl %eax, %edx;                                                            \
  92   movl errno@GOT(%ecx), %ecx;                                                 \
  93   movl %edx, (%ecx);                                                          \
  94   movl $-1, %eax;                                                             \
  95   ret;
  96 #endif  /* _LIBC_REENTRANT */
  97 #endif  /* PIC */
  98
  99 /* Linux takes system call arguments in registers:
 100
 101         syscall number  %eax         call-clobbered
 102         arg 1           %ebx         call-saved
 103         arg 2           %ecx         call-clobbered
 104         arg 3           %edx         call-clobbered
 105         arg 4           %esi         call-saved
 106         arg 5           %edi         call-saved
 107
 108    The stack layout upon entering the function is:
 109
 110         20(%esp)        Arg# 5
 111         16(%esp)        Arg# 4
 112         12(%esp)        Arg# 3
 113          8(%esp)        Arg# 2
 114          4(%esp)        Arg# 1
 115           (%esp)        Return address
 116
 117    (Of course a function with say 3 arguments does not have entries for
 118    arguments 4 and 5.)
 119
 120    The following code tries hard to be optimal.  A general assumption
 121    (which is true according to the data books I have) is that
 122
 123         2 * xchg        is more expensive than  pushl + movl + popl
 124
 125    Beside this a neat trick is used.  The calling conventions for Linux
 126    tell that among the registers used for parameters %ecx and %edx need
 127    not be saved.  Beside this we may clobber this registers even when
 128    they are not used for parameter passing.
 129
 130    As a result one can see below that we save the content of the %ebx
 131    register in the %edx register when we have less than 3 arguments
 132    (2 * movl is less expensive than pushl + popl).
 133
 134    Second unlike for the other registers we don't save the content of
 135    %ecx and %edx when we have more than 1 and 2 registers resp.
 136
 137    The code below might look a bit long but we have to take care for
 138    the pipelined processors (i586 and up).  Here the `pushl' and `popl'
 139    instructions are marked as NP (not pairable) but the exception is
 140    two consecutive of these instruction.  This gives no penalty on
 141    i386 and i486 processors though.  */
 142
 143 #undef  DO_CALL
 144 #define DO_CALL(args, syscall_name)                                           \
 145     PUSHARGS_##args                                                           \
 146     DOARGS_##args                                                             \
 147     movl $SYS_ify (syscall_name), %eax;                                       \
 148     int $0x80                                                                 \
 149     POPARGS_##args
 150
 151 #define PUSHARGS_0      /* No arguments to push.  */
 152 #define DOARGS_0        /* No arguments to frob.  */
 153 #define POPARGS_0       /* No arguments to pop.  */
 154 #define _PUSHARGS_0     /* No arguments to push.  */
 155 #define _DOARGS_0(n)    /* No arguments to frob.  */
 156 #define _POPARGS_0      /* No arguments to pop.  */
 157
 158 #define PUSHARGS_1      movl %ebx, %edx; PUSHARGS_0
 159 #define DOARGS_1        _DOARGS_1 (4)
 160 #define POPARGS_1       POPARGS_0; movl %edx, %ebx
 161 #define _PUSHARGS_1     pushl %ebx; _PUSHARGS_0
 162 #define _DOARGS_1(n)    movl n(%esp), %ebx; _DOARGS_0(n-4)
 163 #define _POPARGS_1      _POPARGS_0; popl %ebx
 164
 165 #define PUSHARGS_2      PUSHARGS_1
 166 #define DOARGS_2        _DOARGS_2 (8)
 167 #define POPARGS_2       POPARGS_1
 168 #define _PUSHARGS_2     _PUSHARGS_1
 169 #define _DOARGS_2(n)    movl n(%esp), %ecx; _DOARGS_1 (n-4)
 170 #define _POPARGS_2      _POPARGS_1
 171
 172 #define PUSHARGS_3      _PUSHARGS_2
 173 #define DOARGS_3        _DOARGS_3 (16)
 174 #define POPARGS_3       _POPARGS_3
 175 #define _PUSHARGS_3     _PUSHARGS_2
 176 #define _DOARGS_3(n)    movl n(%esp), %edx; _DOARGS_2 (n-4)
 177 #define _POPARGS_3      _POPARGS_2
 178
 179 #define PUSHARGS_4      _PUSHARGS_4
 180 #define DOARGS_4        _DOARGS_4 (24)
 181 #define POPARGS_4       _POPARGS_4
 182 #define _PUSHARGS_4     pushl %esi; _PUSHARGS_3
 183 #define _DOARGS_4(n)    movl n(%esp), %esi; _DOARGS_3 (n-4)
 184 #define _POPARGS_4      _POPARGS_3; popl %esi
 185
 186 #define PUSHARGS_5      _PUSHARGS_5
 187 #define DOARGS_5        _DOARGS_5 (32)
 188 #define POPARGS_5       _POPARGS_5
 189 #define _PUSHARGS_5     pushl %edi; _PUSHARGS_4
 190 #define _DOARGS_5(n)    movl n(%esp), %edi; _DOARGS_4 (n-4)
 191 #define _POPARGS_5      _POPARGS_4; popl %edi
 192
 193 #endif  /* ASSEMBLER */
 194
 195 #endif /* linux/i386/sysdep.h */