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Diffstat (limited to 'sysdeps/i386/elf/start.S')
| -rw-r--r-- | sysdeps/i386/elf/start.S | 86 |
1 files changed, 86 insertions, 0 deletions
diff --git a/sysdeps/i386/elf/start.S b/sysdeps/i386/elf/start.S new file mode 100644 index 0000000000..5c29ce412a --- /dev/null +++ b/sysdeps/i386/elf/start.S @@ -0,0 +1,86 @@ +/* Startup code compliant to the ELF i386 ABI. +Copyright (C) 1995 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 Library General Public License as +published by the Free Software Foundation; either version 2 of the +License, or (at your option) any later version. + +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 +Library General Public License for more details. + +You should have received a copy of the GNU Library General Public +License along with the GNU C Library; see the file COPYING.LIB. If +not, write to the Free Software Foundation, Inc., 675 Mass Ave, +Cambridge, MA 02139, USA. */ + +/* 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: + + %edx 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. + + %esp The stack contains the arguments and environment: + 0(%esp) argc + 4(%esp) argv[0] + ... + (4*argc)(%esp) NULL + (4*(argc+1))(%esp) envp[0] + ... + NULL +*/ + + .text + .globl _start +_start: + /* Clear the frame pointer. The ABI suggests this be done, to mark + the outermost frame obviously. */ + movl $0, %ebp + + /* %edx contains the address of the shared library termination + function, which we will register with `atexit' to be called by + `exit'. I suspect that on some systems, and when statically + linked, this will not be set by anything to any function + pointer; hopefully it will be zero so we don't try to call + random pointers. */ + testl %edx + jeq nofini + pushl %edx + call atexit + addl $4, %esp +nofini: + + /* Do essential libc initialization. In statically linked + programs under the GNU Hurd, this is what sets up the + arguments on the stack for the code below. */ + call __libc_init_first + + /* Extract the arguments and environment as encoded on the stack + and set up the arguments for `main': argc, argv, envp. */ + popl %esi /* Pop the argument count. */ + leal 4(%esp,%esi,4), %eax /* envp = &argv[argc + 1] */ + movl %eax, _environ /* Store it in the global variable. */ + pushl %eax /* Push third argument: envp. */ + leal 4(%esp), %eax /* argv starts just above that word. */ + pushl %eax /* Push second argument: argv. */ + pushl %esi /* Push first argument: argc. */ + + /* Call `_init', which is the entry point to our own `.init' + section; and register with `atexit' to have `exit' call + `_fini', which is the entry point to our own `.fini' section. */ + call _init + pushl $_fini + call atexit + addl $4, %esp + + /* Call the user's main function, and exit with its value. */ + call main + pushl %eax + call exit /* This should never return. */ + hlt /* Crash if somehow it does return. */ |