| 1 | /* Startup code for Nios II |
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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 | The stack pointer, sp, will point to the argument count on the stack. |
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| 43 | The initial state of the stack when a userspace process is started is: |
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| 44 | |
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| 45 | Purpose Start Address Length |
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| 46 | Unspecified High Addresses |
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| 47 | Referenced strings, etc. Varies |
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| 48 | Unspecified |
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| 49 | Null auxilliary vector entry 4bytes |
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| 50 | Auxilliary vector entries 8bytes each |
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| 51 | NULL terminator for envp 4bytes |
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| 52 | Environment pointers sp+8+4*argc 4bytes each |
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| 53 | NULL terminator for argv sp+4+4*argc 4bytes |
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| 54 | Argument pointers sp+4 4bytes each |
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| 55 | Argument count sp 4bytes |
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| 56 | Unspecified Low Addresses |
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| 57 | |
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| 58 | If the application should register a destructor function with atexit, |
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| 59 | the pointer will be placed in r4. Otherwise r4 will be zero. |
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| 60 | |
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| 61 | The contents of all other registers are unspecified. User code should |
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| 62 | set fp to zero to mark the end of the frame chain. |
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| 63 | |
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| 64 | The auxilliary vector is a series of pairs of 32-bit tag and 32-bit |
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| 65 | value, terminated by an AT_NULL tag. |
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| 66 | */ |
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| 67 | |
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| 68 | .text |
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| 69 | .globl _start |
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| 70 | .type _start,%function |
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| 71 | _start: |
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| 72 | /* Set up the global pointer. */ |
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| 73 | movhi gp, %hiadj(_gp) |
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| 74 | addi gp, gp, %lo(_gp) |
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| 75 | |
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| 76 | /* Save the stack pointer. */ |
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| 77 | mov r2, sp |
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| 78 | |
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| 79 | /* Create room on the stack for the fini, rtld_fini and stack_end args |
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| 80 | to __libc_start_main. */ |
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| 81 | subi sp, sp, 12 |
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| 82 | |
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| 83 | /* Push stack_end */ |
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| 84 | stw r2, 8(sp) |
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| 85 | |
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| 86 | /* Push rtld_fini */ |
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| 87 | stw r4, 4(sp) |
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| 88 | |
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| 89 | /* Set up the GOT pointer. */ |
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| 90 | nextpc r22 |
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| 91 | 1: movhi r2, %hiadj(_gp_got - 1b) |
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| 92 | addi r2, r2, %lo(_gp_got - 1b) |
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| 93 | add r22, r22, r2 |
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| 94 | |
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| 95 | /* Used to be fini. */ |
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| 96 | stw zero, 0(sp) |
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| 97 | |
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| 98 | /* Used to be init. */ |
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| 99 | mov r7, zero |
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| 100 | |
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| 101 | /* r6 == argv */ |
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| 102 | addi r6, sp, 16 |
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| 103 | |
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| 104 | /* r5 == argc */ |
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| 105 | ldw r5, 12(sp) |
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| 106 | |
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| 107 | /* r4 == main */ |
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| 108 | movhi r4, %call_hiadj(main) |
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| 109 | addi r4, r4, %call_lo(main) |
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| 110 | add r4, r4, r22 |
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| 111 | ldw r4, 0(r4) |
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| 112 | |
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| 113 | /* fp == 0 */ |
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| 114 | mov fp, zero |
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| 115 | |
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| 116 | /* __libc_start_main (main, argc, argv, init, fini, rtld_fini, |
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| 117 | stack_end) */ |
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| 118 | |
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| 119 | /* Let the libc call main and exit with its return code. */ |
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| 120 | movhi r2, %call_hiadj(__libc_start_main) |
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| 121 | addi r2, r2, %call_lo(__libc_start_main) |
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| 122 | add r2, r2, r22 |
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| 123 | ldw r2, 0(r2) |
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| 124 | callr r2 |
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| 125 | |
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| 126 | /* should never get here....*/ |
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| 127 | movhi r2, %call_hiadj(abort) |
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| 128 | addi r2, r2, %call_lo(abort) |
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| 129 | add r2, r2, r22 |
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| 130 | ldw r2, 0(r2) |
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| 131 | callr r2 |
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| 132 | |
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| 133 | /* Define a symbol for the first piece of initialized data. */ |
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| 134 | .data |
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| 135 | .globl __data_start |
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| 136 | __data_start: |
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| 137 | .long 0 |
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| 138 | .weak data_start |
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| 139 | data_start = __data_start |
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| 140 | |
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