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