mirror of git://sourceware.org/git/glibc.git
136 lines
4.6 KiB
C
136 lines
4.6 KiB
C
/* Copyright (C) 1992, 1993, 1995 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper, <drepper@gnu.ai.mit.edu>, August 1995.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Library General Public License as
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published by the Free Software Foundation; either version 2 of the
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License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Library General Public License for more details.
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You should have received a copy of the GNU Library General Public
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License along with the GNU C Library; see the file COPYING.LIB. If
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not, write to the Free Software Foundation, Inc., 675 Mass Ave,
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Cambridge, MA 02139, USA. */
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/* In the Linux/ELF world, C symbols are asm symbols. */
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#define NO_UNDERSCORES
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/* There is some commonality. */
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#include <sysdeps/unix/i386/sysdep.h>
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/* For Linux we can use the system call table in the header file
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/usr/include/asm/unistd.h
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of the kernel. But these symbols do not follow the SYS_* syntax
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so we have to redefine the `SYS_ify' macro here. */
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#undef SYS_ify
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#ifdef __STDC__
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# define SYS_ify(syscall_name) __NR_##syscall_name
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#else
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# define SYS_ify(syscall_name) __NR_/**/syscall_name
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#endif
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#ifdef ASSEMBLER
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/* Linux uses a negative return value to indicate syscall errors, unlike
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most Unices, which use the condition codes' carry flag. */
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#undef PSEUDO
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#define PSEUDO(name, syscall_name, args) \
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.text; \
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.globl syscall_error; \
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ENTRY (name) \
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movl $SYS_ify (syscall_name), %eax; \
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DO_CALL (args); \
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testl %eax, %eax; \
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jl JUMPTARGET (syscall_error)
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/* We define our own ENTRY macro because the alignment should be 16 for ELF. */
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#undef ENTRY
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#define ENTRY(name) \
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ASM_GLOBAL_DIRECTIVE C_SYMBOL_NAME (name); \
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ASM_TYPE_DIRECTIVE (C_SYMBOL_NAME (name), @function) \
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.align 16; \
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C_LABEL (name)
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/* Linux takes system call arguments in registers:
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syscall number %eax call-clobbered
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arg 1 %ebx call-saved
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arg 2 %ecx call-clobbered
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arg 3 %edx call-clobbered
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arg 4 %esi call-saved
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arg 5 %edi call-saved
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The stack layout upon entering the function is:
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20(%esp) Arg# 5
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16(%esp) Arg# 4
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12(%esp) Arg# 3
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8(%esp) Arg# 2
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4(%esp) Arg# 1
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(%esp) Return address
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(Of course a function with say 3 arguments does not have entries for
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arguments 4 and 5.)
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The following code tries hard to be optimal. A general assuption
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(which is true accoriding to the data books I have) is that
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2 * xchg is more expensive than pushl + movl + popl
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Beside this a neat trick is used. The calling conventions for Linux
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tell that among the registers used for parameters %ecx and %edx need
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not be saved. Beside this we may clobber this registers even when
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they are not used for parameter passing.
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As a result one can see below that we save the content of the %ebx
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register in the %edx register when we have less than 3 arguments
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(2 * movl is less expensive than pushl + popl).
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Second unlike for the other registers we don't save the content of
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%ecx and %edx when we have than 1 and 2 registers resp. */
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#undef DO_CALL
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#define DO_CALL(args) \
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DOARGS_##args \
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int $0x80; \
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UNDOARGS_##args
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#define DOARGS_0 /* No arguments to frob. */
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#define UNDOARGS_0 /* No arguments to unfrob. */
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#define _DOARGS_0(n) /* No arguments to frob. */
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#define _UNDOARGS_0 /* No arguments to unfrob. */
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#define DOARGS_1 movl %ebx, %edx; movl 4(%esp), %ebx; DOARGS_0
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#define UNDOARGS_1 UNDOARGS_0; movl %edx, %ebx
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#define _DOARGS_1(n) pushl %ebx; movl n+4(%esp), %ebx; _DOARGS_0 (n)
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#define _UNDOARGS_1 _UNDOARGS_0; popl %ebx
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#define DOARGS_2 movl 8(%esp), %ecx; DOARGS_1
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#define UNDOARGS_2 UNDOARGS_1
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#define _DOARGS_2(n) movl n(%esp), %ecx; _DOARGS_1 (n-4)
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#define _UNDOARGS_2 _UNDOARGS_1
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#define DOARGS_3 _DOARGS_3 (12)
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#define UNDOARGS_3 _UNDOARGS_3
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#define _DOARGS_3(n) movl n(%esp), %edx; _DOARGS_2 (n-4)
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#define _UNDOARGS_3 _UNDOARGS_2
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#define DOARGS_4 _DOARGS_4 (16)
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#define UNDOARGS_4 _UNDOARGS_4
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#define _DOARGS_4(n) pushl %esi; movl n+4(%esp), %esi; _DOARGS_3 (n)
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#define _UNDOARGS_4 _UNDOARGS_3; popl %esi
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#define DOARGS_5 _DOARGS_5 (20)
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#define UNDOARGS_5 _UNDOARGS_5
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#define _DOARGS_5(n) pushl %edi; movl n+4(%esp), %edi; _DOARGS_4 (n)
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#define _UNDOARGS_5 _UNDOARGS_4; popl %edi
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#endif /* ASSEMBLER */
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