1/* Startup code for Nios II
2   Copyright (C) 1995-2022 Free Software Foundation, Inc.
3   This file is part of the GNU C Library.
4
5   The GNU C Library is free software; you can redistribute it and/or
6   modify it under the terms of the GNU Lesser General Public
7   License as published by the Free Software Foundation; either
8   version 2.1 of the License, or (at your option) any later version.
9
10   In addition to the permissions in the GNU Lesser General Public
11   License, the Free Software Foundation gives you unlimited
12   permission to link the compiled version of this file with other
13   programs, and to distribute those programs without any restriction
14   coming from the use of this file. (The GNU Lesser General Public
15   License restrictions do apply in other respects; for example, they
16   cover modification of the file, and distribution when not linked
17   into another program.)
18
19   Note that people who make modified versions of this file are not
20   obligated to grant this special exception for their modified
21   versions; it is their choice whether to do so. The GNU Lesser
22   General Public License gives permission to release a modified
23   version without this exception; this exception also makes it
24   possible to release a modified version which carries forward this
25   exception.
26
27   The GNU C Library is distributed in the hope that it will be useful,
28   but WITHOUT ANY WARRANTY; without even the implied warranty of
29   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
30   Lesser General Public License for more details.
31
32   You should have received a copy of the GNU Lesser General Public
33   License along with the GNU C Library.  If not, see
34   <https://www.gnu.org/licenses/>.  */
35
36/* This is the canonical entry point, usually the first thing in the text
37   segment.
38
39	Note that the code in the .init section has already been run.
40	This includes _init and _libc_init
41
42	The stack pointer, sp, will point to the argument count on the stack.
43	The initial state of the stack when a userspace process is started is:
44
45	    Purpose			Start Address	Length
46	    Unspecified			High Addresses
47	    Referenced strings, etc.			Varies
48	    Unspecified
49	    Null auxilliary vector entry		4bytes
50	    Auxilliary vector entries			8bytes each
51	    NULL terminator for envp			4bytes
52	    Environment pointers	sp+8+4*argc	4bytes each
53	    NULL terminator for argv	sp+4+4*argc	4bytes
54	    Argument pointers		sp+4		4bytes each
55	    Argument count		sp		4bytes
56	    Unspecified			Low Addresses
57
58	If the application should register a destructor function with atexit,
59	the pointer will be placed in r4. Otherwise r4 will be zero.
60
61	The contents of all other registers are unspecified. User code should
62	set fp to zero to mark the end of the frame chain.
63
64	The auxilliary vector is a series of pairs of 32-bit tag and 32-bit
65	value, terminated by an AT_NULL tag.
66*/
67
68	.text
69	.globl _start
70	.type _start,%function
71_start:
72	/* Set up the global pointer.  */
73	movhi	gp, %hiadj(_gp)
74	addi	gp, gp, %lo(_gp)
75
76	/* Save the stack pointer.  */
77	mov	r2, sp
78
79	/* Create room on the stack for the fini, rtld_fini and stack_end args
80	   to __libc_start_main. */
81	subi	sp, sp, 12
82
83	/* Push stack_end */
84	stw	r2, 8(sp)
85
86	/* Push rtld_fini */
87	stw	r4, 4(sp)
88
89	/* Set up the GOT pointer.  */
90	nextpc	r22
911:	movhi	r2, %hiadj(_gp_got - 1b)
92	addi	r2, r2, %lo(_gp_got - 1b)
93	add	r22, r22, r2
94
95	/* Used to be fini.  */
96	stw	zero, 0(sp)
97
98	/* Used to be init.  */
99	mov	r7, zero
100
101	/* r6 == argv */
102	addi	r6, sp, 16
103
104	/* r5 == argc */
105	ldw	r5, 12(sp)
106
107	/* r4 == main */
108	movhi	r4, %call_hiadj(main)
109	addi	r4, r4, %call_lo(main)
110	add	r4, r4, r22
111	ldw	r4, 0(r4)
112
113	/* fp == 0 */
114	mov	fp, zero
115
116	/* __libc_start_main (main, argc, argv, init, fini, rtld_fini,
117			      stack_end) */
118
119	/* Let the libc call main and exit with its return code.  */
120	movhi	r2, %call_hiadj(__libc_start_main)
121	addi	r2, r2, %call_lo(__libc_start_main)
122	add	r2, r2, r22
123	ldw	r2, 0(r2)
124	callr	r2
125
126	/* should never get here....*/
127	movhi	r2, %call_hiadj(abort)
128	addi	r2, r2, %call_lo(abort)
129	add	r2, r2, r22
130	ldw	r2, 0(r2)
131	callr	r2
132
133/* Define a symbol for the first piece of initialized data.  */
134	.data
135	.globl __data_start
136__data_start:
137	.long 0
138	.weak data_start
139	data_start = __data_start
140