| 1 | /* Startup code for ARM & ELF |
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| 2 | Copyright (C) 1995-2022 Free Software Foundation, Inc. |
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| 3 | This file is part of the GNU C Library. |
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| 4 | |
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| 5 | The GNU C Library is free software; you can redistribute it and/or |
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| 6 | modify it under the terms of the GNU Lesser General Public |
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| 7 | License as published by the Free Software Foundation; either |
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| 8 | version 2.1 of the License, or (at your option) any later version. |
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| 9 | |
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| 10 | In addition to the permissions in the GNU Lesser General Public |
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| 11 | License, the Free Software Foundation gives you unlimited |
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| 12 | permission to link the compiled version of this file with other |
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| 13 | programs, and to distribute those programs without any restriction |
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| 14 | coming from the use of this file. (The GNU Lesser General Public |
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| 15 | License restrictions do apply in other respects; for example, they |
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| 16 | cover modification of the file, and distribution when not linked |
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| 17 | into another program.) |
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| 18 | |
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| 19 | Note that people who make modified versions of this file are not |
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| 20 | obligated to grant this special exception for their modified |
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| 21 | versions; it is their choice whether to do so. The GNU Lesser |
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| 22 | General Public License gives permission to release a modified |
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| 23 | version without this exception; this exception also makes it |
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| 24 | possible to release a modified version which carries forward this |
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| 25 | exception. |
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| 26 | |
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| 27 | The GNU C Library is distributed in the hope that it will be useful, |
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| 28 | but WITHOUT ANY WARRANTY; without even the implied warranty of |
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| 29 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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| 30 | Lesser General Public License for more details. |
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| 31 | |
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| 32 | You should have received a copy of the GNU Lesser General Public |
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| 33 | License along with the GNU C Library. If not, see |
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| 34 | <https://www.gnu.org/licenses/>. */ |
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| 35 | |
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| 36 | /* This is the canonical entry point, usually the first thing in the text |
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| 37 | segment. |
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| 38 | |
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| 39 | Note that the code in the .init section has already been run. |
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| 40 | This includes _init and _libc_init |
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| 41 | |
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| 42 | |
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| 43 | At this entry point, most registers' values are unspecified, except: |
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| 44 | |
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| 45 | a1 Contains a function pointer to be registered with `atexit'. |
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| 46 | This is how the dynamic linker arranges to have DT_FINI |
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| 47 | functions called for shared libraries that have been loaded |
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| 48 | before this code runs. |
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| 49 | |
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| 50 | sp The stack contains the arguments and environment: |
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| 51 | 0(sp) argc |
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| 52 | 4(sp) argv[0] |
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| 53 | ... |
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| 54 | (4*argc)(sp) NULL |
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| 55 | (4*(argc+1))(sp) envp[0] |
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| 56 | ... |
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| 57 | NULL |
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| 58 | */ |
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| 59 | |
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| 60 | /* Tag_ABI_align8_preserved: This code preserves 8-byte |
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| 61 | alignment in any callee. */ |
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| 62 | .eabi_attribute 25, 1 |
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| 63 | /* Tag_ABI_align8_needed: This code may require 8-byte alignment from |
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| 64 | the caller. */ |
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| 65 | .eabi_attribute 24, 1 |
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| 66 | |
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| 67 | #if defined(__thumb2__) |
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| 68 | .thumb |
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| 69 | .syntax unified |
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| 70 | #endif |
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| 71 | |
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| 72 | .text |
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| 73 | .globl _start |
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| 74 | .type _start,#function |
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| 75 | _start: |
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| 76 | /* Protect against unhandled exceptions. */ |
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| 77 | .fnstart |
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| 78 | /* Clear the frame pointer and link register since this is the outermost frame. */ |
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| 79 | mov fp, #0 |
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| 80 | mov lr, #0 |
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| 81 | |
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| 82 | /* Pop argc off the stack and save a pointer to argv */ |
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| 83 | pop { a2 } |
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| 84 | mov a3, sp |
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| 85 | |
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| 86 | /* Push stack limit */ |
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| 87 | push { a3 } |
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| 88 | |
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| 89 | /* Push rtld_fini */ |
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| 90 | push { a1 } |
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| 91 | |
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| 92 | #ifdef PIC |
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| 93 | ldr sl, .L_GOT |
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| 94 | adr a4, .L_GOT |
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| 95 | add sl, sl, a4 |
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| 96 | |
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| 97 | mov a4, #0 /* Used to be init. */ |
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| 98 | push { a4 } /* Used to be fini. */ |
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| 99 | |
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| 100 | ldr a1, .L_GOT+4 /* main */ |
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| 101 | ldr a1, [sl, a1] |
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| 102 | |
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| 103 | /* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end) */ |
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| 104 | /* Let the libc call main and exit with its return code. */ |
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| 105 | bl __libc_start_main(PLT) |
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| 106 | #else |
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| 107 | |
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| 108 | mov a4, #0 /* Used to init. */ |
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| 109 | push { a4 } /* Used to fini. */ |
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| 110 | ldr a1, =main |
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| 111 | |
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| 112 | /* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end) */ |
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| 113 | /* Let the libc call main and exit with its return code. */ |
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| 114 | bl __libc_start_main |
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| 115 | #endif |
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| 116 | |
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| 117 | /* should never get here....*/ |
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| 118 | bl abort |
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| 119 | |
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| 120 | #ifdef PIC |
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| 121 | .align 2 |
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| 122 | .L_GOT: |
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| 123 | .word _GLOBAL_OFFSET_TABLE_ - .L_GOT |
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| 124 | .word main(GOT) |
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| 125 | #endif |
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| 126 | |
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| 127 | .cantunwind |
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| 128 | .fnend |
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| 129 | |
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| 130 | /* Define a symbol for the first piece of initialized data. */ |
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| 131 | .data |
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| 132 | .globl __data_start |
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| 133 | __data_start: |
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| 134 | .long 0 |
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| 135 | .weak data_start |
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| 136 | data_start = __data_start |
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| 137 | |
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