1/* Startup code compliant to the 64 bit S/390 ELF ABI.
2 Copyright (C) 2001-2020 Free Software Foundation, Inc.
3 Contributed by Martin Schwidefsky (schwidefsky@de.ibm.com).
4 This file is part of the GNU C Library.
5
6 The GNU C Library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
10
11 In addition to the permissions in the GNU Lesser General Public
12 License, the Free Software Foundation gives you unlimited
13 permission to link the compiled version of this file with other
14 programs, and to distribute those programs without any restriction
15 coming from the use of this file. (The GNU Lesser General Public
16 License restrictions do apply in other respects; for example, they
17 cover modification of the file, and distribution when not linked
18 into another program.)
19
20 Note that people who make modified versions of this file are not
21 obligated to grant this special exception for their modified
22 versions; it is their choice whether to do so. The GNU Lesser
23 General Public License gives permission to release a modified
24 version without this exception; this exception also makes it
25 possible to release a modified version which carries forward this
26 exception.
27
28 The GNU C Library is distributed in the hope that it will be useful,
29 but WITHOUT ANY WARRANTY; without even the implied warranty of
30 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
31 Lesser General Public License for more details.
32
33 You should have received a copy of the GNU Lesser General Public
34 License along with the GNU C Library; if not, see
35 <https://www.gnu.org/licenses/>. */
36
37#include <sysdep.h>
38
39/*
40 This is the canonical entry point, usually the first thing in the text
41 segment. Most registers' values are unspecified, except for:
42
43 %r14 Contains a function pointer to be registered with `atexit'.
44 This is how the dynamic linker arranges to have DT_FINI
45 functions called for shared libraries that have been loaded
46 before this code runs.
47
48 %r15 The stack contains the arguments and environment:
49 0(%r15) argc
50 8(%r15) argv[0]
51 ...
52 (8*argc)(%r15) NULL
53 (8*(argc+1))(%r15) envp[0]
54 ...
55 NULL
56*/
57
58 .text
59 .globl _start
60 .type _start,@function
61_start:
62 cfi_startproc
63 /* Mark r14 as undefined in order to stop unwinding here! */
64 cfi_undefined (r14)
65 /* Load argc and argv from stack. */
66 la %r4,8(%r15) # get argv
67 lg %r3,0(%r15) # get argc
68
69 /* Align the stack to a double word boundary. */
70 lghi %r0,-16
71 ngr %r15,%r0
72
73 /* Setup a stack frame and a parameter area. */
74 aghi %r15,-176 # make room on stack
75 xc 0(8,%r15),0(%r15) # clear back-chain
76
77 /* Set up arguments for __libc_start_main:
78 main, argc, argv, envp, _init, _fini, rtld_fini, stack_end
79 Note that envp will be determined later in __libc_start_main.
80 */
81 stmg %r14,%r15,160(%r15) # store rtld_fini/stack_end to parameter area
82 la %r7,160(%r15)
83 larl %r6,__libc_csu_fini # load pointer to __libc_csu_fini
84 larl %r5,__libc_csu_init # load pointer to __libc_csu_init
85
86 /* Ok, now branch to the libc main routine. */
87#ifdef PIC
88 larl %r2,main@GOTENT # load pointer to main
89 lg %r2,0(%r2)
90 brasl %r14,__libc_start_main@plt
91#else
92 larl %r2,main # load pointer to main
93 brasl %r14,__libc_start_main
94#endif
95
96 /* Crash if __libc_start_main returns. */
97 .word 0
98
99 cfi_endproc
100
101 /* Define a symbol for the first piece of initialized data. */
102 .data
103 .globl __data_start
104__data_start:
105 .long 0
106 .weak data_start
107 data_start = __data_start