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.
74 lines
2 KiB
ArmAsm
74 lines
2 KiB
ArmAsm
/* Startup code for ARC.
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Copyright (C) 2020-2021 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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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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#define __ASSEMBLY__ 1
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#include <entry.h>
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#include <sysdep.h>
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#ifndef ENTRY_POINT
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# error ENTRY_POINT needs to be defined for ARC
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#endif
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/* When we enter this piece of code, the program stack looks like this:
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argc argument counter (integer)
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argv[0] program name (pointer)
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argv[1...N] program args (pointers)
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argv[argc-1] end of args (integer)
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NULL
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env[0...N] environment variables (pointers)
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NULL. */
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ENTRY (ENTRY_POINT)
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/* Needed to make gdb backtraces stop here. */
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.cfi_label .Ldummy
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cfi_undefined (blink)
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mov fp, 0
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ld_s r1, [sp] /* argc. */
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mov_s r5, r0 /* rltd_fini. */
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add_s r2, sp, 4 /* argv. */
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and sp, sp, -8
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mov r6, sp
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/* __libc_start_main (main, argc, argv, init, fini, rtld_fini, stack_end). */
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mov_s r3, 0 /* Used to be init. */
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mov r4, 0 /* Used to be fini. */
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#ifdef SHARED
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ld r0, [pcl, @main@gotpc]
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bl __libc_start_main@plt
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#else
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mov_s r0, main
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bl __libc_start_main
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#endif
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/* Should never get here. */
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flag 1
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END (ENTRY_POINT)
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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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