crti.asm

gcc-you can use this code to learn something about gcc, and inquire further into linux,

/* Copyright (C) 2001, 2002 Free Software Foundation, Inc.
   Contributed by Hans-Peter Nilsson <[e-mail]>

This file 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 2, or (at your option) any
later version.

In addition to the permissions in the GNU General Public License, the
Free Software Foundation gives you unlimited permission to link the
compiled version of this file into combinations with other programs,
and to distribute those combinations without any restriction coming
from the use of this file.  (The General Public License restrictions
do apply in other respects; for example, they cover modification of
the file, and distribution when not linked into a combine
executable.)

This file 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 this program; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */

% This is the crt0 equivalent for mmix-knuth-mmixware, for setting up
% things for compiler-generated assembly-code and for setting up things
% between where the simulator calls and main, and shutting things down on
% the way back.  There's an actual crt0.o elsewhere, but that's a dummy.

% This file and the GCC output are supposed to be *reasonably*
% mmixal-compatible to enable people to re-use output with Knuth's mmixal.
% However, forward references are used more freely: we are using the
% binutils tools.  Users of mmixal beware; you will sometimes have to
% re-order things or use temporary variables.

% Users of mmixal will want to set up 8H and 9H to be .text and .data
% respectively, so the compiler can switch between them pretending they're
% segments.

% This little treasure is here so the 32 lowest address bits of user data
% will not be zero.  Because of truncation, that would cause test-case
% gcc.c-torture/execute/980701-1.c to incorrectly fail.

	.data	! mmixal:= 8H LOC Data_Segment
	.p2align 3
	LOC @+(8-@)@7
	OCTA 2009

	.text	! mmixal:= 9H LOC 8B; LOC #100
	.global Main

% The __Stack_start symbol is provided by the link script.
stackpp	OCTA __Stack_start

% "Main" is the magic symbol the simulator jumps to.  We want to go
% on to "main".
% We need to set rG explicitly to avoid hard-to-debug situations.
Main	SETL	$255,32
	PUT	rG,$255

% Initialize the stack pointer.  It is supposedly made a global
% zero-initialized (allowed to change) register in crtn.asm; we use the
% explicit number.
	GETA	$255,stackpp
	LDOU	$254,$255,0

% Make sure we get more than one mem, to simplify counting cycles.
	LDBU	$255,$1,0
	LDBU	$255,$1,1

	PUSHJ	$2,_init

#ifdef __MMIX_ABI_GNU__
% Copy argc and argv from their initial position to argument registers
% where necessary.
	SET	$231,$0
	SET	$232,$1
#else
% For the mmixware ABI, we need to move arguments.  The return value will
% appear in $0.
	SET	$2,$1
	SET	$1,$0
#endif

	PUSHJ	$0,main
	JMP	exit

% Provide the first part of _init and _fini.  Save the return address on the
% register stack.  We eventually ignore the return address of these
% PUSHJ:s, so it doesn't matter that whether .init and .fini code calls
% functions or where they store rJ.  We shouldn't get there, so abort
% (TRAP Halt) if that happens.

	.section .init,"ax",@progbits
	.global	_init
_init:
	GET	$0,:rJ
	PUSHJ	$1,0F
	SETL	$255,255
	TRAP	0,0,0
0H	IS	@

% Register _fini to be executed as the last atexit function.
#ifdef __MMIX_ABI_GNU__
	GETA	$231,_fini
#else
	GETA	$1,_fini
#endif
	PUSHJ	$0,atexit

	.section .fini,"ax",@progbits
	.global	_fini
_fini:
	GET	$0,:rJ
	PUSHJ	$1,0F
	SETL	$255,255
	TRAP	0,0,0
0H	IS	@