/* Startup code compliant to the ELF x86-64 ABI.

   Copyright (C) 2001-2018 Free Software Foundation, Inc.

   This file is part of the GNU C Library.

   Contributed by Andreas Jaeger <aj@suse.de>, 2001.

   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

   <http://www.gnu.org/licenses/>.  */

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

   segment.  The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry

   point runs, most registers' values are unspecified, except for:

   %rdx		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.

   %rsp		The stack contains the arguments and environment:

		0(%rsp)				argc

		LP_SIZE(%rsp)			argv[0]

		...

		(LP_SIZE*argc)(%rsp)		NULL

		(LP_SIZE*(argc+1))(%rsp)	envp[0]

		...

						NULL

*/

#include <sysdep.h>

ENTRY (_start)

	/* Clearing frame pointer is insufficient, use CFI.  */

	cfi_undefined (rip)

	/* Clear the frame pointer.  The ABI suggests this be done, to mark

	   the outermost frame obviously.  */

	xorl %ebp, %ebp

	/* Extract the arguments as encoded on the stack and set up

	   the arguments for __libc_start_main (int (*main) (int, char **, char **),

		   int argc, char *argv,

		   void (*init) (void), void (*fini) (void),

		   void (*rtld_fini) (void), void *stack_end).

	   The arguments are passed via registers and on the stack:

	main:		%rdi

	argc:		%rsi

	argv:		%rdx

	init:		%rcx

	fini:		%r8

	rtld_fini:	%r9

	stack_end:	stack.	*/

	mov %RDX_LP, %R9_LP	/* Address of the shared library termination

				   function.  */

#ifdef __ILP32__

	mov (%rsp), %esi	/* Simulate popping 4-byte argument count.  */

	add $4, %esp

#else

	popq %rsi		/* Pop the argument count.  */

#endif

	/* argv starts just at the current stack top.  */

	mov %RSP_LP, %RDX_LP

	/* Align the stack to a 16 byte boundary to follow the ABI.  */

	and  $~15, %RSP_LP

	/* Push garbage because we push 8 more bytes.  */

	pushq %rax

	/* Provide the highest stack address to the user code (for stacks

	   which grow downwards).  */

	pushq %rsp

#ifdef PIC

	/* Pass address of our own entry points to .fini and .init.  */

	mov __libc_csu_fini@GOTPCREL(%rip), %R8_LP

	mov __libc_csu_init@GOTPCREL(%rip), %RCX_LP

	mov main@GOTPCREL(%rip), %RDI_LP

#else

	/* Pass address of our own entry points to .fini and .init.  */

	mov $__libc_csu_fini, %R8_LP

	mov $__libc_csu_init, %RCX_LP

	mov $main, %RDI_LP

#endif

	/* Call the user's main function, and exit with its value.

	   But let the libc call main.  Since __libc_start_main in

	   libc.so is called very early, lazy binding isn't relevant

	   here.  Use indirect branch via GOT to avoid extra branch

	   to PLT slot.  In case of static executable, ld in binutils

	   2.26 or above can convert indirect branch into direct

	   branch.  */

	call *__libc_start_main@GOTPCREL(%rip)

	hlt			/* Crash if somehow `exit' does return.	 */

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