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035c012e32
It turns out the startup code in csu/elf-init.c has a perfect pair of ROP gadgets (see Marco-Gisbert and Ripoll-Ripoll, "return-to-csu: A New Method to Bypass 64-bit Linux ASLR"). These functions are not needed in dynamically-linked binaries because DT_INIT/DT_INIT_ARRAY are already processed by the dynamic linker. However, the dynamic linker skipped the main program for some reason. For maximum backwards compatibility, this is not changed, and instead, the main map is consulted from __libc_start_main if the init function argument is a NULL pointer. For statically linked binaries, the old approach based on linker symbols is still used because there is nothing else available. A new symbol version __libc_start_main@@GLIBC_2.34 is introduced because new binaries running on an old libc would not run their ELF constructors, leading to difficult-to-debug issues.
107 lines
3.3 KiB
ArmAsm
107 lines
3.3 KiB
ArmAsm
/* Startup code for SH & ELF.
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Copyright (C) 1999-2021 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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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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<https://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.
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Note that the code in the .init section has already been run.
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This includes _init and _libc_init
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At this entry point, most registers' values are unspecified, except:
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r4 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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sp The stack contains the arguments and environment:
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0(sp) argc
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4(sp) argv[0]
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...
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(4*argc)(sp) NULL
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(4*(argc+1))(sp) envp[0]
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...
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NULL
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*/
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.text
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.globl _start
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.type _start,@function
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_start:
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/* Clear the frame pointer since this is the outermost frame. */
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mov #0, r14
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/* Pop argc off the stack and save a pointer to argv */
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mov.l @r15+,r5
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mov r15, r6
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/* Push the last arguments to main() onto the stack */
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mov.l r4,@-r15
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mov.l r14,@-r15 /* Used to be fini. */
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/* Set up the other arguments for main() that go in registers */
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mov.l L_main,r4
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mov #0,r7 /* Used to be init. */
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/* __libc_start_main (main, argc, argv, init, fini, rtld_fini) */
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/* Let the libc call main and exit with its return code. */
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mov.l L_libc_start_main,r1
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jsr @r1
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nop
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/* should never get here....*/
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mov.l L_abort,r1
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jsr @r1
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nop
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.align 2
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L_main:
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.long main
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L_libc_start_main:
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.long __libc_start_main
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L_abort:
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.long abort
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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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.global __fpscr_values
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__fpscr_values:
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.long 0
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.long 0x80000
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