1/* Startup code compliant to the ELF i386 ABI.
  2   Copyright (C) 1995-2025 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.  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
1291:	movl	(%esp), %ebx
130	ret
131#endif
132
133#if defined PIC && !defined SHARED
134__wrap_main:
135	jmp	main@PLT
136#endif
137END (_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