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Diffstat (limited to 'payloads/libpayload/i386/head.S')
-rw-r--r-- | payloads/libpayload/i386/head.S | 85 |
1 files changed, 85 insertions, 0 deletions
diff --git a/payloads/libpayload/i386/head.S b/payloads/libpayload/i386/head.S new file mode 100644 index 0000000000..1278bdf4ed --- /dev/null +++ b/payloads/libpayload/i386/head.S @@ -0,0 +1,85 @@ +/* + * This file is part of the libpayload project. + * + * Copyright (C) 2008 Advanced Micro Devices, Inc. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. 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. + * 3. 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 AND CONTRIBUTORS ``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 OR CONTRIBUTORS 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. + */ + + .global _entry, _leave + .text + .align 4 + +/* Our entry point - assume that the CPU is in + * 32 bit protected mode and all segments are in a + * flat model. Thats our operating mode, so we won't + * change anything + */ + +_entry: + call _init + + /* We're back - go back to the bootloader */ + ret + +/* This function saves off the previous stack and + switches us to our own execution enviornment +*/ + +_init: + /* No interrupts, please */ + cli + + /* Get the current stack pointer */ + movl %esp, %esi + + movl _istack, %ebx + + /* lret needs %cs in the stack, so copy it over */ + movw %cs, 4(%ebx) + + /* Exchange the current stack pointer for the one in + the initial stack (which happens to be the new + stack pointer) */ + + xchgl %esi, 16(%ebx) + + /* Set the new stack pointer */ + movl %esi, %esp + + /* Return into the main entry function + and go + */ + + lret + +_leave: + movl _istack, %ebx + + /* Restore the stack pointer from the storage area */ + movl 16(%ebx), %esp + + /* Return to the original context */ + lret + |