mes/lib/freebsd/x86-mes-gcc/hello-mes.S

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/*
* GNU Mes --- Maxwell Equations of Software
* Copyright © 2019 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
*
* This file is part of GNU Mes.
*
* GNU Mes 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 Software Foundation; either version 3 of the License, or (at
* your option) any later version.
*
* GNU Mes is distributed in the hope that it will be useful, but
* WITHOUT 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
* along with GNU Mes. If not, see <http://www.gnu.org/licenses/>.
*/
/** Commentary: */
/* Using gdb, esp. GUD in GNU Emacs is recommended
M-x gdb-display-disassembly-buffer
M-x gdb-display-io-buffer
set disassemble-next-line on
break _start
run
info registers
si
p/x $eax
RET
...
*/
/** Code: */
SYS_exit = 1 /* Linux syscalls. */
SYS_write = 4
stdout = 1 /* File discriptor */
.globl _start /* Magic linker symbol: --entry-address. */
.text /* Program text. */
_start:
mov $SYS_write,%eax /* System call function: write, in %eax. */
push $(bye-hello) /* 3rd parameter: byte count. */
push $hello /* 2nd parameter: address. */
push $stdout /* 1st parameter: file descriptor. */
push $0 /* ?? */
int $0x80 /* Call system. */
mov $SYS_exit,%eax /* System call function: exit, in %eax. */
push $0 /* 1st parameter: exit status. */
push $0 /* ?? */
int $0x80 /* Call system. */
hlt /* Should not be reached. */
.data
hello: .ascii "Hello, GNU Mes!\n"
bye: .byte 0