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Diffstat (limited to 'sysdeps/x86_64/elf/start.S')
| -rw-r--r-- | sysdeps/x86_64/elf/start.S | 95 |
1 files changed, 95 insertions, 0 deletions
diff --git a/sysdeps/x86_64/elf/start.S b/sysdeps/x86_64/elf/start.S new file mode 100644 index 0000000000..600aaf2566 --- /dev/null +++ b/sysdeps/x86_64/elf/start.S @@ -0,0 +1,95 @@ +/* Startup code compliant to the ELF x86-64 ABI. + Copyright (C) 2001 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. + + 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, write to the Free + Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 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: + + %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 + 8(%rsp) argv[0] + ... + (8*argc)(%rsp) NULL + (8*(argc+1))(%rsp) envp[0] + ... + NULL +*/ + +#include "bp-sym.h" + + .text + .globl _start + .type _start,@function +_start: + /* Clear the frame pointer. The ABI suggests this be done, to mark + the outermost frame obviously. */ + xorq %rbp, %rbp + + /* 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. */ + + movq %rdx, %r9 /* Address of the shared library termination + function. */ + popq %rsi /* Pop the argument count. */ + movq %rsp, %rdx /* argv starts just at the current stack top. */ + /* Align the stack to a 16 byte boundary to follow the ABI. */ + andq $~15, %rsp + + pushq %rax /* Push garbage because we push 8 more bytes. */ + + /* Provide the highest stack address to the user code (for stacks + which grow downwards). */ + pushq %rsp + + /* Pass address of our own entry points to .fini and .init. */ + movq $_fini, %r8 + movq $_init, %rcx + + movq $BP_SYM (main), %rdi + + /* Call the user's main function, and exit with its value. + But let the libc call main. */ + call BP_SYM (__libc_start_main) + + hlt /* Crash if somehow `exit' does return. */ + +/* 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 |