/* Startup code compliant to the ELF s390 ABI. Copyright (C) 2000-2019 Free Software Foundation, Inc. Contributed by Martin Schwidefsky (schwidefsky@de.ibm.com). 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 . */ #include /* This is the canonical entry point, usually the first thing in the text segment. Most registers' values are unspecified, except for: %r14 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. %r15 The stack contains the arguments and environment: 0(%r15) argc 4(%r15) argv[0] ... (4*argc)(%r15) NULL (4*(argc+1))(%r15) envp[0] ... NULL */ .text .globl _start .type _start,@function _start: cfi_startproc /* Mark r14 as undefined in order to stop unwinding here! */ cfi_undefined (r14) /* Check if the kernel provides highgprs facility if needed by the binary. */ lr %r6,%r15 la %r6,4(%r6) /* Skip the argument counter. */ .L11: l %r5,0(%r6) /* Skip the argument vector. */ la %r6,4(%r6) ltr %r5,%r5 jne .L11 .L12: l %r5,0(%r6) /* Skip the environment vector. */ la %r6,4(%r6) ltr %r5,%r5 jne .L12 /* Usually the auxiliary vector can be expected directly after the environment variables. But we have to skip extra zeros because the loader might have removed unsecure variables for setuid programs. */ .L26: l %r5,0(%r6) la %r6,4(%r6) ltr %r5,%r5 jz .L26 ahi %r6,-4 /* Obtain the needed values from the auxiliary vector. */ lhi %r7,16 /* AT_HWCAP */ lhi %r8,3 /* AT_PHDR */ lhi %r9,5 /* AT_PHNUM */ lhi %r2,4 /* AT_PHENT */ .L13: l %r5,0(%r6) clr %r5,%r7 jne .L15 l %r10,4(%r6) /* r10 = AT_HWCAP value. */ .L15: clr %r5,%r8 jne .L16 l %r11,4(%r6) /* r11 = AT_PHDR value. */ .L16: clr %r5,%r9 jne .L17 l %r12,4(%r6) /* r12 = AT_PHNUM value. */ .L17: clr %r5,%r2 jne .L18 l %r0,4(%r6) /* r0 = AT_PHENT value. */ .L18: ltr %r5,%r5 la %r6,8(%r6) jnz .L13 /* Locate the ELF header by looking for the first PT_LOAD segment with a p_offset of zero. */ lr %r4,%r11 /* Backup AT_PHDR. */ lhi %r7,1 /* PT_LOAD id */ lhi %r8,0 .L19: cl %r7,0(%r4) /* p_type == PT_LOAD? */ jne .L20 cl %r8,4(%r4) /* p_offset == 0? */ jne .L20 l %r9,8(%r4) /* r9 = PT_LOAD.p_vaddr <- ELF header address */ j .L24 .L20: alr %r4,%r0 /* r4 += AT_PHENT value */ brct %r12,.L19 j .+2 /* Trap, there must be such a phdr. */ .L24: lr %r4,%r11 /* Backup AT_PHDR. */ lhi %r2,6 /* PT_PHDR id */ .L23: cl %r2,0(%r4) jne .L22 l %r3,8(%r4) /* r3 = PT_PHDR p_vaddr */ j .L25 .L22: alr %r4,%r0 /* r4 += AT_PHENT value */ brct %r12,.L23 j .L14 /* No PT_PHDR found - skip checking. */ .L25: slr %r11,%r3 /* AT_PHDR - PT_PHDR.p_vaddr (relocation offset)*/ alr %r9,%r11 /* PT_LOAD.p_vaddr += relocation offset */ l %r5,36(%r9) /* Load the e_flags field. */ tml %r5,1 jz .L14 /* Binary does not require highgprs facility. */ tml %r10,512 /* Check the AT_HWCAP value. */ jz 2 /* Trap if no highgprs facility available. */ .L14: /* Setup pointer to literal pool of _start */ basr %r13,0 .L0: ahi %r13,.Llit-.L0 /* load argc and argv from stack */ la %r4,4(%r15) # get argv l %r3,0(%r15) # get argc /* align the stack to a double word boundary */ lhi %r0,-8 nr %r15,%r0 /* Setup a stack frame and a parameter area */ ahi %r15,-104 # make room on stack xc 0(4,%r15),0(%r15) # clear back-chain /* set up arguments for __libc_start_main: main, argc, argv, envp, _init, _fini, rtld_fini, stack_end Note that envp will be determined later in __libc_start_main */ stm %r14,%r15,96(%r15) # store rtld_fini/stack_end to parameter area la %r7,96(%r15) l %r6,.L2-.Llit(%r13) # load pointer to __libc_csu_fini l %r5,.L1-.Llit(%r13) # load pointer to __libc_csu_init l %r2,.L3-.Llit(%r13) # load pointer to main l %r1,.L4-.Llit(%r13) # load pointer to __libc_start_main #ifdef PIC l %r12,.L5-.Llit(%r13) # load .got pointer la %r6,0(%r13,%r6) la %r5,0(%r13,%r5) la %r12,0(%r13,%r12) l %r2,0(%r12,%r2) la %r1,0(%r13,%r1) #endif /* ok, now branch to the libc main routine */ basr %r14,%r1 /* crash if __libc_start_main returns */ .word 0 cfi_endproc .Llit: #ifndef PIC .L1: .long __libc_csu_init .L2: .long __libc_csu_fini .L3: .long main .L4: .long __libc_start_main #else .L1: .long __libc_csu_init-.Llit .L2: .long __libc_csu_fini-.Llit .L3: .long main@GOT .L4: .long __libc_start_main@plt-.Llit .L5: .long _GLOBAL_OFFSET_TABLE_-.Llit #endif /* 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