1/* Startup code compliant to the ELF i386 ABI. 2 Copyright (C) 1995-2022 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. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry 38 point runs, most registers' values are unspecified, except for: 39 40 %edx Contains a function pointer to be registered with `atexit'. 41 This is how the dynamic linker arranges to have DT_FINI 42 functions called for shared libraries that have been loaded 43 before this code runs. 44 45 %esp The stack contains the arguments and environment: 46 0(%esp) argc 47 4(%esp) argv[0] 48 ... 49 (4*argc)(%esp) NULL 50 (4*(argc+1))(%esp) envp[0] 51 ... 52 NULL 53*/ 54 55#include <sysdep.h> 56 57ENTRY (_start) 58 /* Clearing frame pointer is insufficient, use CFI. */ 59 cfi_undefined (eip) 60 /* Clear the frame pointer. The ABI suggests this be done, to mark 61 the outermost frame obviously. */ 62 xorl %ebp, %ebp 63 64 /* Extract the arguments as encoded on the stack and set up 65 the arguments for `main': argc, argv. envp will be determined 66 later in __libc_start_main. */ 67 popl %esi /* Pop the argument count. */ 68 movl %esp, %ecx /* argv starts just at the current stack top.*/ 69 70 /* Before pushing the arguments align the stack to a 16-byte 71 (SSE needs 16-byte alignment) boundary to avoid penalties from 72 misaligned accesses. Thanks to Edward Seidl <seidl@janed.com> 73 for pointing this out. */ 74 andl $0xfffffff0, %esp 75 pushl %eax /* Push garbage because we allocate 76 28 more bytes. */ 77 78 /* Provide the highest stack address to the user code (for stacks 79 which grow downwards). */ 80 pushl %esp 81 82 pushl %edx /* Push address of the shared library 83 termination function. */ 84 85#ifdef PIC 86 /* Load PIC register. */ 87 call 1f 88 addl $_GLOBAL_OFFSET_TABLE_, %ebx 89 90 /* This used to be the addresses of .fini and .init. */ 91 pushl $0 92 pushl $0 93 94 pushl %ecx /* Push second argument: argv. */ 95 pushl %esi /* Push first argument: argc. */ 96 97# ifdef SHARED 98 pushl main@GOT(%ebx) 99# else 100 /* Avoid relocation in static PIE since _start is called before 101 it is relocated. Don't use "leal main@GOTOFF(%ebx), %eax" 102 since main may be in a shared object. Linker will convert 103 "movl main@GOT(%ebx), %eax" to "leal main@GOTOFF(%ebx), %eax" 104 if main is defined locally. */ 105 movl main@GOT(%ebx), %eax 106 pushl %eax 107# endif 108 109 /* Call the user's main function, and exit with its value. 110 But let the libc call main. */ 111 call __libc_start_main@PLT 112#else 113 /* This used to be the addresses of .fini and .init. */ 114 pushl $0 115 pushl $0 116 117 pushl %ecx /* Push second argument: argv. */ 118 pushl %esi /* Push first argument: argc. */ 119 120 pushl $main 121 122 /* Call the user's main function, and exit with its value. 123 But let the libc call main. */ 124 call __libc_start_main 125#endif 126 127 hlt /* Crash if somehow `exit' does return. */ 128 129#ifdef PIC 1301: movl (%esp), %ebx 131 ret 132#endif 133END (_start) 134 135/* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so 136 meaningless since we don't support machines < 80386. */ 137 .section .rodata 138 .globl _fp_hw 139_fp_hw: .long 3 140 .size _fp_hw, 4 141 .type _fp_hw,@object 142 143/* Define a symbol for the first piece of initialized data. */ 144 .data 145 .globl __data_start 146__data_start: 147 .long 0 148 .weak data_start 149 data_start = __data_start 150