1 | /* Startup code compliant to the ELF i386 ABI. |
2 | Copyright (C) 1995-2024 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 | |
57 | ENTRY (_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. This also avoid rely on linker optimization to |
102 | transform 'movl main@GOT(%ebx), %eax' to 'leal main@GOTOFF(%ebx)' |
103 | if main is defined locally. */ |
104 | leal __wrap_main@GOTOFF(%ebx), %eax |
105 | pushl %eax |
106 | # endif |
107 | |
108 | /* Call the user's main function, and exit with its value. |
109 | But let the libc call main. */ |
110 | call __libc_start_main@PLT |
111 | #else |
112 | /* This used to be the addresses of .fini and .init. */ |
113 | pushl $0 |
114 | pushl $0 |
115 | |
116 | pushl %ecx /* Push second argument: argv. */ |
117 | pushl %esi /* Push first argument: argc. */ |
118 | |
119 | pushl $main |
120 | |
121 | /* Call the user's main function, and exit with its value. |
122 | But let the libc call main. */ |
123 | call __libc_start_main |
124 | #endif |
125 | |
126 | hlt /* Crash if somehow `exit' does return. */ |
127 | |
128 | #ifdef PIC |
129 | 1: movl (%esp), %ebx |
130 | ret |
131 | #endif |
132 | |
133 | #if defined PIC && !defined SHARED |
134 | __wrap_main: |
135 | jmp main@PLT |
136 | #endif |
137 | END (_start) |
138 | |
139 | /* To fulfill the System V/i386 ABI we need this symbol. Yuck, it's so |
140 | meaningless since we don't support machines < 80386. */ |
141 | .section .rodata |
142 | .globl _fp_hw |
143 | _fp_hw: .long 3 |
144 | .size _fp_hw, 4 |
145 | .type _fp_hw,@object |
146 | |
147 | /* Define a symbol for the first piece of initialized data. */ |
148 | .data |
149 | .globl __data_start |
150 | __data_start: |
151 | .long 0 |
152 | .weak data_start |
153 | data_start = __data_start |
154 | |