1/* Copyright (C) 2011-2018 Free Software Foundation, Inc. 2 3 The GNU C Library is free software; you can redistribute it and/or 4 modify it under the terms of the GNU Lesser General Public 5 License as published by the Free Software Foundation; either 6 version 2.1 of the License, or (at your option) any later version. 7 8 In addition to the permissions in the GNU Lesser General Public 9 License, the Free Software Foundation gives you unlimited 10 permission to link the compiled version of this file with other 11 programs, and to distribute those programs without any restriction 12 coming from the use of this file. (The GNU Lesser General Public 13 License restrictions do apply in other respects; for example, they 14 cover modification of the file, and distribution when not linked 15 into another program.) 16 17 Note that people who make modified versions of this file are not 18 obligated to grant this special exception for their modified 19 versions; it is their choice whether to do so. The GNU Lesser 20 General Public License gives permission to release a modified 21 version without this exception; this exception also makes it 22 possible to release a modified version which carries forward this 23 exception. 24 25 The GNU C Library is distributed in the hope that it will be useful, 26 but WITHOUT ANY WARRANTY; without even the implied warranty of 27 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 28 Lesser General Public License for more details. 29 30 You should have received a copy of the GNU Lesser General Public 31 License along with the GNU C Library. If not, see 32 <http://www.gnu.org/licenses/>. */ 33 34/* This is the canonical entry point, usually the first thing in the text 35 segment. The ELF standard tells us that the stack is set up like this on 36 entry (the left side is the offset from "sp"), in units of 37 __SIZEOF_POINTER__ entries: 38 39 +0 argc 40 +1 argv[0] 41 ... 42 +(argc+1) NULL 43 +(argc+2) envp[0] 44 ... 45 NULL 46 ... ElfInfo 47 48 The ElfInfo is pairs of key/value long words following the envp 49 pointers and terminated by a zero-valued key. 50 51 Although not mandated by the standard, it happens to be the case 52 that we store the actual argv and envp strings immediately after 53 the ElfInfo data on the stack. 54 55 On entry r0 points to the shared library termination function, or 0 56 if there isn't one. 57*/ 58 59#include <features.h> 60#include <sysdep.h> 61#include <arch/abi.h> 62 63/* Just create no-ops if we don't support PC-relative PLT relocations. */ 64#ifdef NO_PLT_PCREL 65# define hw2_last_plt(x) 0 66# define hw1_plt(x) 0 67# define hw0_plt(x) 0 68#endif 69 70 .text 71 .global _start 72 .type _start,@function 73 .align 8 74_start: 75 /* Linux starts us with sp pointing at the conventional Elf layout, 76 but we need to allow two "caller" words for our ABI convention. */ 77 { 78 /* Load argc (stored as a "long", equivalent to a pointer type). */ 79 LD_PTR r1, sp 80 81 /* Save incoming 'sp', which points to the Elf argument block. */ 82 move r52, sp 83 } 84 85 { 86 /* Allocate stack frame callee space for __libc_start_main. */ 87 ADDI_PTR r12, sp, -(2 * REGSIZE) 88 } 89 90 { 91 /* Get our PC. */ 92 lnk r13 93 94 /* sp is not necessarily properly aligned on startup because 95 of the way ld.so pops off leading argv elements. So align it. */ 96 andi sp, r12, -8 97 } 98.Lmy_pc: 99 100 { 101 /* Pass the address of the shared library termination function. */ 102 move r5, r0 103 104 /* Compute location where __libc_start_main's caller is supposed to 105 store its frame pointer. */ 106 ADDI_PTR r12, sp, REGSIZE 107 108 /* Zero out callee space for return address. Unnecessary but free. 109 This is just paranoia to help backtracing not go awry. */ 110 st sp, zero 111 } 112 { 113 /* Zero out our frame pointer for __libc_start_main. */ 114 st r12, zero 115 116 /* Zero out lr to make __libc_start_main the end of backtrace. */ 117 move lr, zero 118 119 /* Compute a pointer to argv. envp will be determined 120 later in __libc_start_main. We set up the first argument 121 (the address of main) below. */ 122 ADDI_PTR r2, r52, __SIZEOF_POINTER__ 123 } 124 { 125 /* Pass the highest stack address to user code. */ 126 ADDI_PTR r6, sp, (2 * REGSIZE) 127 128 /* Pass address of main() in r0, and of our own entry 129 points to .fini and .init in r3 and r4. */ 130 moveli r0, hw2_last(main - .Lmy_pc) 131 } 132 { 133 shl16insli r0, r0, hw1(main - .Lmy_pc) 134 moveli r3, hw2_last(_init - .Lmy_pc) 135 } 136 { 137 shl16insli r0, r0, hw0(main - .Lmy_pc) 138 shl16insli r3, r3, hw1(_init - .Lmy_pc) 139 } 140 { 141 ADD_PTR r0, r0, r13 142 shl16insli r3, r3, hw0(_init - .Lmy_pc) 143 } 144 { 145 moveli r12, hw2_last_plt(__uClibc_main - .Lmy_pc) 146 ADD_PTR r3, r3, r13 147 } 148 { 149 shl16insli r12, r12, hw1_plt(__uClibc_main - .Lmy_pc) 150 moveli r4, hw2_last(_fini - .Lmy_pc) 151 } 152 { 153 shl16insli r12, r12, hw0_plt(__uClibc_main - .Lmy_pc) 154 shl16insli r4, r4, hw1(_fini - .Lmy_pc) 155 } 156 { 157 ADD_PTR r12, r12, r13 158 shl16insli r4, r4, hw0(_fini - .Lmy_pc) 159 } 160 { 161 ADD_PTR r4, r4, r13 162#ifdef NO_PLT_PCREL 163 j plt(__uClibc_main) 164#else 165 jr r12 166#endif 167 } 168 169 { 170 /* Tell backtracer to give up (_start has no caller). */ 171 info INFO_OP_CANNOT_BACKTRACE 172 } 173.size _start, .-_start 174 175/* Define a symbol for the first piece of initialized data. */ 176 .data 177 .global __data_start 178 .align 8 179__data_start: 180 .long 0 181 .weak data_start 182 data_start = __data_start 183