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ac187dc4ab
Since __libc_start_main in libc.so is called very early, lazy binding isn't relevant. Always call __libc_start_main with indirect branch via GOT to avoid extra branch to PLT slot. In case of static executable, ld in binutils 2.26 or above can convert indirect branch into direct branch: 0000000000400a80 <_start>: 400a80: 31 ed xor %ebp,%ebp 400a82: 49 89 d1 mov %rdx,%r9 400a85: 5e pop %rsi 400a86: 48 89 e2 mov %rsp,%rdx 400a89: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp 400a8d: 50 push %rax 400a8e: 54 push %rsp 400a8f: 49 c7 c0 20 1b 40 00 mov $0x401b20,%r8 400a96: 48 c7 c1 90 1a 40 00 mov $0x401a90,%rcx 400a9d: 48 c7 c7 c0 03 40 00 mov $0x4003c0,%rdi 400aa4: 67 e8 96 09 00 00 addr32 callq 401440 <__libc_start_main> 400aaa: f4 hlt * sysdeps/x86_64/start.S (_start): Always indirect branch to __libc_start_main via GOT.
132 lines
4.6 KiB
ArmAsm
132 lines
4.6 KiB
ArmAsm
/* Startup code compliant to the ELF x86-64 ABI.
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Copyright (C) 2001-2016 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Andreas Jaeger <aj@suse.de>, 2001.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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In addition to the permissions in the GNU Lesser General Public
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License, the Free Software Foundation gives you unlimited
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permission to link the compiled version of this file with other
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programs, and to distribute those programs without any restriction
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coming from the use of this file. (The GNU Lesser General Public
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License restrictions do apply in other respects; for example, they
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cover modification of the file, and distribution when not linked
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into another program.)
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Note that people who make modified versions of this file are not
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obligated to grant this special exception for their modified
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versions; it is their choice whether to do so. The GNU Lesser
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General Public License gives permission to release a modified
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version without this exception; this exception also makes it
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possible to release a modified version which carries forward this
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exception.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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/* This is the canonical entry point, usually the first thing in the text
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segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry
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point runs, most registers' values are unspecified, except for:
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%rdx Contains a function pointer to be registered with `atexit'.
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This is how the dynamic linker arranges to have DT_FINI
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functions called for shared libraries that have been loaded
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before this code runs.
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%rsp The stack contains the arguments and environment:
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0(%rsp) argc
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LP_SIZE(%rsp) argv[0]
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...
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(LP_SIZE*argc)(%rsp) NULL
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(LP_SIZE*(argc+1))(%rsp) envp[0]
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...
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NULL
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*/
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#include <sysdep.h>
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ENTRY (_start)
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/* Clearing frame pointer is insufficient, use CFI. */
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cfi_undefined (rip)
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/* Clear the frame pointer. The ABI suggests this be done, to mark
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the outermost frame obviously. */
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xorl %ebp, %ebp
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/* Extract the arguments as encoded on the stack and set up
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the arguments for __libc_start_main (int (*main) (int, char **, char **),
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int argc, char *argv,
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void (*init) (void), void (*fini) (void),
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void (*rtld_fini) (void), void *stack_end).
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The arguments are passed via registers and on the stack:
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main: %rdi
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argc: %rsi
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argv: %rdx
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init: %rcx
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fini: %r8
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rtld_fini: %r9
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stack_end: stack. */
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mov %RDX_LP, %R9_LP /* Address of the shared library termination
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function. */
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#ifdef __ILP32__
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mov (%rsp), %esi /* Simulate popping 4-byte argument count. */
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add $4, %esp
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#else
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popq %rsi /* Pop the argument count. */
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#endif
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/* argv starts just at the current stack top. */
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mov %RSP_LP, %RDX_LP
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/* Align the stack to a 16 byte boundary to follow the ABI. */
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and $~15, %RSP_LP
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/* Push garbage because we push 8 more bytes. */
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pushq %rax
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/* Provide the highest stack address to the user code (for stacks
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which grow downwards). */
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pushq %rsp
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#ifdef SHARED
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/* Pass address of our own entry points to .fini and .init. */
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mov __libc_csu_fini@GOTPCREL(%rip), %R8_LP
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mov __libc_csu_init@GOTPCREL(%rip), %RCX_LP
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mov main@GOTPCREL(%rip), %RDI_LP
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#else
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/* Pass address of our own entry points to .fini and .init. */
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mov $__libc_csu_fini, %R8_LP
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mov $__libc_csu_init, %RCX_LP
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mov $main, %RDI_LP
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#endif
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/* Call the user's main function, and exit with its value.
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But let the libc call main. Since __libc_start_main in
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libc.so is called very early, lazy binding isn't relevant
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here. Use indirect branch via GOT to avoid extra branch
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to PLT slot. In case of static executable, ld in binutils
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2.26 or above can convert indirect branch into direct
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branch. */
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call *__libc_start_main@GOTPCREL(%rip)
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hlt /* Crash if somehow `exit' does return. */
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END (_start)
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/* Define a symbol for the first piece of initialized data. */
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.data
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.globl __data_start
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__data_start:
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.long 0
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.weak data_start
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data_start = __data_start
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