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91181954f9
To enable building glibc with branch protection, assembly code needs BTI landing pads and ELF object file markings in the form of a GNU property note. The landing pads are unconditionally added to all functions that may be indirectly called. When the code segment is not mapped with PROT_BTI these instructions are nops. They are kept in the code when BTI is not supported so that the layout of performance critical code is unchanged across configurations. The GNU property notes are only added when there is support for BTI in the toolchain, because old binutils does not handle the notes right. (Does not know how to merge them nor to put them in PT_GNU_PROPERTY segment instead of PT_NOTE, and some versions of binutils emit warnings about the unknown GNU property. In such cases the produced libc binaries would not have valid ELF marking so BTI would not be enabled.) Note: functions using ENTRY or ENTRY_ALIGN now start with an additional BTI c, so alignment of the following code changes, but ENTRY_ALIGN_AND_PAD was fixed so there is no change to the existing code layout. Some string functions may need to be tuned for optimal performance after this commit. Co-authored-by: Szabolcs Nagy <szabolcs.nagy@arm.com> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
114 lines
3.1 KiB
ArmAsm
114 lines
3.1 KiB
ArmAsm
/* Copyright (C) 1995-2020 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 License as
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published by the Free Software Foundation; either version 2.1 of the
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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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#include <sysdep.h>
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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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x0/w0 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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8(sp) argv[0]
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...
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(8*argc)(sp) NULL
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(8*(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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BTI_C
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/* Create an initial frame with 0 LR and FP */
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mov x29, #0
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mov x30, #0
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/* Setup rtld_fini in argument register */
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mov x5, x0
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/* Load argc and a pointer to argv */
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ldr PTR_REG (1), [sp, #0]
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add x2, sp, #PTR_SIZE
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/* Setup stack limit in argument register */
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mov x6, sp
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#ifdef PIC
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# ifdef SHARED
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adrp x0, :got:main
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ldr PTR_REG (0), [x0, #:got_lo12:main]
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adrp x3, :got:__libc_csu_init
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ldr PTR_REG (3), [x3, #:got_lo12:__libc_csu_init]
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adrp x4, :got:__libc_csu_fini
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ldr PTR_REG (4), [x4, #:got_lo12:__libc_csu_fini]
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# else
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adrp x0, __wrap_main
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add x0, x0, :lo12:__wrap_main
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adrp x3, __libc_csu_init
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add x3, x3, :lo12:__libc_csu_init
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adrp x4, __libc_csu_fini
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add x4, x4, :lo12:__libc_csu_fini
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# endif
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#else
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/* Set up the other arguments in registers */
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MOVL (0, main)
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MOVL (3, __libc_csu_init)
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MOVL (4, __libc_csu_fini)
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#endif
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/* __libc_start_main (main, argc, argv, init, fini, rtld_fini,
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stack_end) */
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/* Let the libc call main and exit with its return code. */
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bl __libc_start_main
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/* should never get here....*/
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bl abort
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#if defined PIC && !defined SHARED
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/* When main is not defined in the executable but in a shared library
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then a wrapper is needed in crt1.o of the static-pie enabled libc,
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because crt1.o and rcrt1.o share code and the later must avoid the
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use of GOT relocations before __libc_start_main is called. */
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__wrap_main:
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b main
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#endif
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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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