glibc/sysdeps/aarch64/start.S

/* Copyright (C) 1995-2022 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   In addition to the permissions in the GNU Lesser General Public
   License, the Free Software Foundation gives you unlimited
   permission to link the compiled version of this file with other
   programs, and to distribute those programs without any restriction
   coming from the use of this file. (The GNU Lesser General Public
   License restrictions do apply in other respects; for example, they
   cover modification of the file, and distribution when not linked
   into another program.)

   Note that people who make modified versions of this file are not
   obligated to grant this special exception for their modified
   versions; it is their choice whether to do so. The GNU Lesser
   General Public License gives permission to release a modified
   version without this exception; this exception also makes it
   possible to release a modified version which carries forward this
   exception.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#include <sysdep.h>

/* This is the canonical entry point, usually the first thing in the text
   segment.

   Note that the code in the .init section has already been run.
   This includes _init and _libc_init


   At this entry point, most registers' values are unspecified, except:

   x0/w0	Contains a function pointer to be registered with `atexit'.
		This is how the dynamic linker arranges to have DT_FINI
		functions called for shared libraries that have been loaded
		before this code runs.

   sp		The stack contains the arguments and environment:
		0(sp)			argc
		8(sp)			argv[0]
		...
		(8*argc)(sp)		NULL
		(8*(argc+1))(sp)	envp[0]
		...
					NULL
 */

	.text
ENTRY(_start)
	/* Create an initial frame with 0 LR and FP */
	cfi_undefined (x30)
	mov	x29, #0
	mov	x30, #0

	/* Setup rtld_fini in argument register */
	mov	x5, x0

	/* Load argc and a pointer to argv */
	ldr	PTR_REG (1), [sp, #0]
	add	x2, sp, #PTR_SIZE

	/* Setup stack limit in argument register */
	mov	x6, sp

#ifdef PIC
# ifdef SHARED
        adrp    x0, :got:main
	ldr     PTR_REG (0), [x0, #:got_lo12:main]
# else
	adrp	x0, __wrap_main
	add	x0, x0, :lo12:__wrap_main
# endif
#else
	/* Set up the other arguments in registers */
	MOVL (0, main)
#endif
	mov	x3, #0		/* Used to be init.  */
	mov	x4, #0		/* Used to be fini.  */

	/* __libc_start_main (main, argc, argv, init, fini, rtld_fini,
			      stack_end) */

	/* Let the libc call main and exit with its return code.  */
	bl	__libc_start_main

	/* should never get here....*/
	bl	abort

#if defined PIC && !defined SHARED
	/* When main is not defined in the executable but in a shared library
	   then a wrapper is needed in crt1.o of the static-pie enabled libc,
	   because crt1.o and rcrt1.o share code and the later must avoid the
	   use of GOT relocations before __libc_start_main is called.  */
__wrap_main:
	BTI_C
	b	main
#endif
END(_start)

	/* Define a symbol for the first piece of initialized data.  */
	.data
	.globl __data_start
__data_start:
	.long 0
	.weak data_start
	data_start = __data_start