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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>
96 lines
2.9 KiB
ArmAsm
96 lines
2.9 KiB
ArmAsm
/* Special .init and .fini section support for AArch64.
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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
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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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/* crti.S puts a function prologue at the beginning of the .init and
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.fini sections and defines global symbols for those addresses, so
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they can be called as functions. The symbols _init and _fini are
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magic and cause the linker to emit DT_INIT and DT_FINI. */
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#include <sysdep.h>
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#include <libc-symbols.h>
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#ifndef PREINIT_FUNCTION
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# define PREINIT_FUNCTION __gmon_start__
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#endif
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#ifndef PREINIT_FUNCTION_WEAK
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# define PREINIT_FUNCTION_WEAK 1
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#endif
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#if PREINIT_FUNCTION_WEAK
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weak_extern (PREINIT_FUNCTION)
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#else
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.hidden PREINIT_FUNCTION
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#endif
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#if PREINIT_FUNCTION_WEAK
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.align 2
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.type call_weak_fn, %function
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call_weak_fn:
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adrp x0, :got:PREINIT_FUNCTION
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ldr PTR_REG (0), [x0, #:got_lo12:PREINIT_FUNCTION]
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cbz x0, 1f
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b PREINIT_FUNCTION
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1:
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RET
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.size call_weak_fn, .-call_weak_fn
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#endif
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.section .init,"ax",%progbits
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.align 2
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.global _init
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.hidden _init
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.type _init, %function
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_init:
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BTI_C
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stp x29, x30, [sp, -16]!
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mov x29, sp
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#if PREINIT_FUNCTION_WEAK
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bl call_weak_fn
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#else
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bl PREINIT_FUNCTION
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#endif
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.section .fini,"ax",%progbits
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.align 2
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.global _fini
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.hidden _fini
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.type _fini, %function
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_fini:
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BTI_C
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stp x29, x30, [sp, -16]!
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mov x29, sp
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