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#
# Copyright (c) 2001-2004 Jakub Jermar
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions
# are met:
#
# - Redistributions of source code must retain the above copyright
#   notice, this list of conditions and the following disclaimer.
# - Redistributions in binary form must reproduce the above copyright
#   notice, this list of conditions and the following disclaimer in the
#   documentation and/or other materials provided with the distribution.
# - The name of the author may not be used to endorse or promote products
#   derived from this software without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
# IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
# OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
# IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
# INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
# NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
# THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#

.text

.global context_save
.global context_restore


## Save current CPU context
#
# Save CPU context to the context_t variable
# pointed by the 1st argument. Returns 1 in EAX.
#
context_save:
    movl 0(%esp),%eax   # the caller's return %eip
    movl 4(%esp),%edx   # address of the kernel_context variable to save context to

    movl %esp,0(%edx)   # %esp -> ctx->sp
    movl %eax,4(%edx)   # %eip -> ctx->pc
    movl %ebx,8(%edx)   # %ebx -> ctx->ebx
    movl %esi,12(%edx)  # %esi -> ctx->esi
    movl %edi,16(%edx)  # %edi -> ctx->edi
    movl %ebp,20(%edx)  # %ebp -> ctx->ebp

    # Save TLS
    movl %gs:0, %eax
    movl %eax, 24(%edx)     # tls -> ctx->tls
    
    xorl %eax,%eax      # context_save returns 1
    incl %eax
    ret


## Restore saved CPU context
#
# Restore CPU context from context_t variable
# pointed by the 1st argument. Returns 0 in EAX.
#
context_restore:
    movl 4(%esp),%eax   # address of the kernel_context variable to restore context from
    movl 0(%eax),%esp   # ctx->sp -> %esp
    movl 4(%eax),%edx   # ctx->pc -> %edx
    movl 8(%eax),%ebx   # ctx->ebx -> %ebx
    movl 12(%eax),%esi  # ctx->esi -> %esi
    movl 16(%eax),%edi  # ctx->edi -> %edi
    movl 20(%eax),%ebp  # ctx->ebp -> %ebp

    movl %edx,0(%esp)   # ctx->pc -> saver's return %eip

    # Set thread local storage
    pushl %edi
    movl 24(%eax), %eax   # Set arg1 to TLS addr
    movl $1, %edi         # Syscall 1
    int $0x30
    popl %edi
    
    xorl %eax,%eax      # context_restore returns 0
    ret