1/* Startup code for ARM & ELF
2 Copyright (C) 1995-2020 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 ldr ip, .L_GOT+4 /* __libc_csu_fini */
98 ldr ip, [sl, ip]
99
100 push { ip } /* Push __libc_csu_fini */
101
102 ldr a4, .L_GOT+8 /* __libc_csu_init */
103 ldr a4, [sl, a4]
104
105 ldr a1, .L_GOT+12 /* main */
106 ldr a1, [sl, a1]
107
108 /* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end) */
109 /* Let the libc call main and exit with its return code. */
110 bl __libc_start_main(PLT)
111#else
112 /* Fetch address of __libc_csu_fini */
113 ldr ip, =__libc_csu_fini
114
115 /* Push __libc_csu_fini */
116 push { ip }
117
118 /* Set up the other arguments in registers */
119 ldr a1, =main
120 ldr a4, =__libc_csu_init
121
122 /* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end) */
123 /* Let the libc call main and exit with its return code. */
124 bl __libc_start_main
125#endif
126
127 /* should never get here....*/
128 bl abort
129
130#ifdef PIC
131 .align 2
132.L_GOT:
133 .word _GLOBAL_OFFSET_TABLE_ - .L_GOT
134 .word __libc_csu_fini(GOT)
135 .word __libc_csu_init(GOT)
136 .word main(GOT)
137#endif
138
139 .cantunwind
140 .fnend
141
142/* Define a symbol for the first piece of initialized data. */
143 .data
144 .globl __data_start
145__data_start:
146 .long 0
147 .weak data_start
148 data_start = __data_start