1/* Startup code compliant to the 64 bit S/390 ELF ABI. 2 Copyright (C) 2001-2022 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#include <sysdep.h> 37 38/* 39 This is the canonical entry point, usually the first thing in the text 40 segment. Most registers' values are unspecified, except for: 41 42 %r14 Contains a function pointer to be registered with `atexit'. 43 This is how the dynamic linker arranges to have DT_FINI 44 functions called for shared libraries that have been loaded 45 before this code runs. 46 47 %r15 The stack contains the arguments and environment: 48 0(%r15) argc 49 8(%r15) argv[0] 50 ... 51 (8*argc)(%r15) NULL 52 (8*(argc+1))(%r15) envp[0] 53 ... 54 NULL 55*/ 56 57 .text 58 .globl _start 59 .type _start,@function 60_start: 61 cfi_startproc 62 /* Mark r14 as undefined in order to stop unwinding here! */ 63 cfi_undefined (r14) 64 /* Load argc and argv from stack. */ 65 la %r4,8(%r15) # get argv 66 lg %r3,0(%r15) # get argc 67 68 /* Align the stack to a double word boundary. */ 69 lghi %r0,-16 70 ngr %r15,%r0 71 72 /* Setup a stack frame and a parameter area. */ 73 aghi %r15,-176 # make room on stack 74 xc 0(8,%r15),0(%r15) # clear back-chain 75 76 /* Set up arguments for __libc_start_main: 77 main, argc, argv, envp, _init, _fini, rtld_fini, stack_end 78 Note that envp will be determined later in __libc_start_main. 79 */ 80 stmg %r14,%r15,160(%r15) # store rtld_fini/stack_end to parameter area 81 la %r7,160(%r15) 82 lghi %r6,0 # Used to be fini. 83 lghi %r5,0 # Used to be init. 84 85 /* Ok, now branch to the libc main routine. */ 86#ifdef PIC 87# ifdef SHARED 88 /* Used for dynamic linked position independent executable. 89 => Scrt1.o */ 90 larl %r2,main@GOTENT # load pointer to main 91 lg %r2,0(%r2) 92# else 93 /* Used for dynamic linked position dependent executable. 94 => crt1.o (glibc configured without --disable-default-pie: 95 PIC is defined) 96 Or for static linked position independent executable. 97 => rcrt1.o (only available if glibc configured without 98 --disable-default-pie: PIC is defined) */ 99 larl %r2,__wrap_main 100# endif 101 brasl %r14,__libc_start_main@plt 102#else 103 /* Used for dynamic/static linked position dependent executable. 104 => crt1.o (glibc configured with --disable-default-pie: 105 PIC and SHARED are not defined) */ 106 larl %r2,main # load pointer to main 107 brasl %r14,__libc_start_main 108#endif 109 110 /* Crash if __libc_start_main returns. */ 111 .word 0 112 113 cfi_endproc 114 115#if defined PIC && !defined SHARED 116 /* When main is not defined in the executable but in a shared library 117 then a wrapper is needed in crt1.o of the static-pie enabled libc, 118 because crt1.o and rcrt1.o share code and the later must avoid the 119 use of GOT relocations before __libc_start_main is called. */ 120__wrap_main: 121 cfi_startproc 122 larl %r1,main@GOTENT # load pointer to main 123 lg %r1,0(%r1) 124 br %r1 125 cfi_endproc 126#endif 127 128 /* Define a symbol for the first piece of initialized data. */ 129 .data 130 .globl __data_start 131__data_start: 132 .long 0 133 .weak data_start 134 data_start = __data_start 135