1/* Startup code for ARM & ELF
2   Copyright (C) 1995-2021 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
43	At this entry point, most registers' values are unspecified, except:
44
45   a1		Contains a function pointer to be registered with `atexit'.
46		This is how the dynamic linker arranges to have DT_FINI
47		functions called for shared libraries that have been loaded
48		before this code runs.
49
50   sp		The stack contains the arguments and environment:
51		0(sp)			argc
52		4(sp)			argv[0]
53		...
54		(4*argc)(sp)		NULL
55		(4*(argc+1))(sp)	envp[0]
56		...
57					NULL
58*/
59
60/* Tag_ABI_align8_preserved: This code preserves 8-byte
61   alignment in any callee.  */
62	.eabi_attribute 25, 1
63/* Tag_ABI_align8_needed: This code may require 8-byte alignment from
64   the caller.  */
65	.eabi_attribute 24, 1
66
67#if defined(__thumb2__)
68	.thumb
69	.syntax unified
70#endif
71
72	.text
73	.globl _start
74	.type _start,#function
75_start:
76       /* Protect against unhandled exceptions.  */
77       .fnstart
78	/* Clear the frame pointer and link register since this is the outermost frame. */
79	mov fp, #0
80	mov lr, #0
81
82	/* Pop argc off the stack and save a pointer to argv */
83	pop { a2 }
84	mov a3, sp
85
86	/* Push stack limit */
87	push { a3 }
88
89	/* Push rtld_fini */
90	push { a1 }
91
92#ifdef PIC
93	ldr sl, .L_GOT
94	adr a4, .L_GOT
95	add sl, sl, a4
96
97	mov a4, #0		/* Used to be init.  */
98	push { a4 }		/* Used to be fini.  */
99
100	ldr a1, .L_GOT+4	/* main */
101	ldr a1, [sl, a1]
102
103	/* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end) */
104	/* Let the libc call main and exit with its return code.  */
105	bl __libc_start_main(PLT)
106#else
107
108	mov a4, #0		/* Used to init.  */
109	push { a4 }		/* Used to fini.  */
110	ldr a1, =main
111
112	/* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end) */
113	/* Let the libc call main and exit with its return code.  */
114	bl __libc_start_main
115#endif
116
117	/* should never get here....*/
118	bl abort
119
120#ifdef PIC
121	.align 2
122.L_GOT:
123	.word _GLOBAL_OFFSET_TABLE_ - .L_GOT
124	.word main(GOT)
125#endif
126
127       .cantunwind
128       .fnend
129
130/* Define a symbol for the first piece of initialized data.  */
131	.data
132	.globl __data_start
133__data_start:
134	.long 0
135	.weak data_start
136	data_start = __data_start
137