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##=============================================================================

##

##      vectors.S

##

##      x86 exception vectors

##

##=============================================================================

## ####ECOSGPLCOPYRIGHTBEGIN####

## -------------------------------------------

## This file is part of eCos, the Embedded Configurable Operating System.

## Copyright (C) 1998, 1999, 2000, 2001, 2002 Free Software Foundation, Inc.

##

## eCos is free software; you can redistribute it and/or modify it under

## the terms of the GNU General Public License as published by the Free

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## version.

##

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## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

## FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

## for more details.

##

## You should have received a copy of the GNU General Public License

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## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.

##

## As a special exception, if other files instantiate templates or use

## macros or inline functions from this file, or you compile this file

## and link it with other works to produce a work based on this file,

## this file does not by itself cause the resulting work to be covered by

## the GNU General Public License. However the source code for this file

## must still be made available in accordance with section (3) of the GNU

## General Public License v2.

##

## This exception does not invalidate any other reasons why a work based

## on this file might be covered by the GNU General Public License.

## -------------------------------------------

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##=============================================================================

#######DESCRIPTIONBEGIN####

##

## Author(s):   bartv

## Contributors:bartv

## Date:        2001-03-16

## Purpose:     Synthetic target startup

## Description: When running on real hardware vectors.S contains

##              initialization code and usually the low-level interrupt and

##              exception support. On the synthetic target the latter is

##              handled by C code. The main initialization that is needed is

##              to jump into the C startup.

##

######DESCRIPTIONEND####

##

##=============================================================================

# According the SVR4/i386 ABI, most registers are undefined. However

# there is some interesting information on the stack:

#     %esp              argc

#     %esp+4            argv[0]

#     ...               argv[1 onwards]

#     %esp + (argc*4)   NULL

#     ...               environ[0]

#     ...               ...

#     ...               NULL

#

# There are some other things that could be done, for example aligning

# the stack to a 16-byte boundary for SSE, but it is not clear which of

# those things are actually useful. The glibc source file

# sysdeps/i386/elf/start.S contains some relevant information.

#==============================================================================

        .file   "vectors.S"

        .extern _hal_synth_user_desc

        .extern _linux_entry

        .data

        .global cyg_hal_sys_argc

cyg_hal_sys_argc:

        .long   0

        .global cyg_hal_sys_argv

cyg_hal_sys_argv:

        .long   0

        .global cyg_hal_sys_environ

cyg_hal_sys_environ:

        .long 0

        .text

        .globl  _start

_start:

        popl    %eax

        movl    %eax, cyg_hal_sys_argc

        movl    %esp, %ebx

        movl    %ebx, cyg_hal_sys_argv

        inc     %eax

        addl    %eax, %eax

        addl    %eax, %eax

        addl    %eax, %ebx

        movl    %ebx, cyg_hal_sys_environ

        // Clear the frame pointer, to facilitate debugging

        xorl    %ebp, %ebp

        // Align the stack to a 16-byte boundary.

        andl    $0xFFFFFFF0, %esp

        // Set up the TLS section. This must be done before any

        // C code gets to run, or -fstack-protector-all will fail.

        // _hal_synth_user_desc is statically initialized in tls.c

        movl    $_hal_synth_user_desc,%ebx

        // Syscall 243, set_thread_area

        movl    $0xf3, %eax

        int     $0x80

        // The syscall may have failed. That should only happen if running

        // on an old kernel which predates set_thread_area(), in which case

        // we are probably also using an old gcc which does not yet support

        // -fstack-protector. There is no obvious way forward if we are trying

        // to run an executable built with recent gcc on an old kernel.

        test    %eax, %eax

        jne     1f

        // gs value = (_hal_synth_user_desc.ud_entry_number * 8) + 3

        movl    _hal_synth_user_desc,%eax

        lea     0x3(,%eax,8),%eax

        mov     %eax,%gs

1:

        jmp     _linux_entry