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glibc/sysdeps/aarch64/sysdep.h
Sudakshina Das 91181954f9 aarch64: Add BTI support to assembly files 
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>
2020-07-08 15:02:37 +01:00

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/* Copyright (C) 1997-2020 Free Software Foundation, Inc.
This file is part of the GNU C Library.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public License as
published by the Free Software Foundation; either version 2.1 of the
License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, see
<https://www.gnu.org/licenses/>. */
#ifndef _AARCH64_SYSDEP_H
#define _AARCH64_SYSDEP_H
#include <sysdeps/generic/sysdep.h>
#ifdef __LP64__
# define AARCH64_R(NAME) R_AARCH64_ ## NAME
# define PTR_REG(n) x##n
# define PTR_LOG_SIZE 3
# define DELOUSE(n)
#else
# define AARCH64_R(NAME) R_AARCH64_P32_ ## NAME
# define PTR_REG(n) w##n
# define PTR_LOG_SIZE 2
# define DELOUSE(n) mov w##n, w##n
#endif
#define PTR_SIZE (1<<PTR_LOG_SIZE)
#ifdef __ASSEMBLER__
/* Syntactic details of assembler. */
#define ASM_SIZE_DIRECTIVE(name) .size name,.-name
/* Branch Target Identitication support. */
#define BTI_C hint 34
#define BTI_J hint 36
/* GNU_PROPERTY_AARCH64_* macros from elf.h for use in asm code. */
#define FEATURE_1_AND 0xc0000000
#define FEATURE_1_BTI 1
#define FEATURE_1_PAC 2
/* Add a NT_GNU_PROPERTY_TYPE_0 note. */
#define GNU_PROPERTY(type, value) \
.section .note.gnu.property, "a"; \
.p2align 3; \
.word 4; \
.word 16; \
.word 5; \
.asciz "GNU"; \
.word type; \
.word 4; \
.word value; \
.word 0; \
.text
/* Add GNU property note with the supported features to all asm code
where sysdep.h is included. */
#if HAVE_AARCH64_BTI
GNU_PROPERTY (FEATURE_1_AND, FEATURE_1_BTI)
#endif
/* Define an entry point visible from C. */
#define ENTRY(name) \
.globl C_SYMBOL_NAME(name); \
.type C_SYMBOL_NAME(name),%function; \
.align 4; \
C_LABEL(name) \
cfi_startproc; \
BTI_C; \
CALL_MCOUNT
/* Define an entry point visible from C. */
#define ENTRY_ALIGN(name, align) \
.globl C_SYMBOL_NAME(name); \
.type C_SYMBOL_NAME(name),%function; \
.p2align align; \
C_LABEL(name) \
cfi_startproc; \
BTI_C; \
CALL_MCOUNT
/* Define an entry point visible from C with a specified alignment and
pre-padding with NOPs. This can be used to ensure that a critical
loop within a function is cache line aligned. Note this version
does not adjust the padding if CALL_MCOUNT is defined. */
#define ENTRY_ALIGN_AND_PAD(name, align, padding) \
.globl C_SYMBOL_NAME(name); \
.type C_SYMBOL_NAME(name),%function; \
.p2align align; \
.rep padding - 1; /* -1 for bti c. */ \
nop; \
.endr; \
C_LABEL(name) \
cfi_startproc; \
BTI_C; \
CALL_MCOUNT
#undef END
#define END(name) \
cfi_endproc; \
ASM_SIZE_DIRECTIVE(name)
/* If compiled for profiling, call `mcount' at the start of each function. */
#ifdef PROF
# define CALL_MCOUNT \
str x30, [sp, #-80]!; \
cfi_adjust_cfa_offset (80); \
cfi_rel_offset (x30, 0); \
stp x0, x1, [sp, #16]; \
cfi_rel_offset (x0, 16); \
cfi_rel_offset (x1, 24); \
stp x2, x3, [sp, #32]; \
cfi_rel_offset (x2, 32); \
cfi_rel_offset (x3, 40); \
stp x4, x5, [sp, #48]; \
cfi_rel_offset (x4, 48); \
cfi_rel_offset (x5, 56); \
stp x6, x7, [sp, #64]; \
cfi_rel_offset (x6, 64); \
cfi_rel_offset (x7, 72); \
mov x0, x30; \
bl mcount; \
ldp x0, x1, [sp, #16]; \
cfi_restore (x0); \
cfi_restore (x1); \
ldp x2, x3, [sp, #32]; \
cfi_restore (x2); \
cfi_restore (x3); \
ldp x4, x5, [sp, #48]; \
cfi_restore (x4); \
cfi_restore (x5); \
ldp x6, x7, [sp, #64]; \
cfi_restore (x6); \
cfi_restore (x7); \
ldr x30, [sp], #80; \
cfi_adjust_cfa_offset (-80); \
cfi_restore (x30);
#else
# define CALL_MCOUNT /* Do nothing. */
#endif
/* Local label name for asm code. */
#ifndef L
# define L(name) .L##name
#endif
/* Load or store to/from a pc-relative EXPR into/from R, using T.
Note R and T are register numbers and not register names. */
#define LDST_PCREL(OP, R, T, EXPR) \
adrp x##T, EXPR; \
OP PTR_REG (R), [x##T, #:lo12:EXPR]; \
/* Load or store to/from a got-relative EXPR into/from R, using T.
Note R and T are register numbers and not register names. */
#define LDST_GLOBAL(OP, R, T, EXPR) \
adrp x##T, :got:EXPR; \
ldr PTR_REG (T), [x##T, #:got_lo12:EXPR]; \
OP PTR_REG (R), [x##T];
/* Load an immediate into R.
Note R is a register number and not a register name. */
#ifdef __LP64__
# define MOVL(R, NAME) \
movz PTR_REG (R), #:abs_g3:NAME; \
movk PTR_REG (R), #:abs_g2_nc:NAME; \
movk PTR_REG (R), #:abs_g1_nc:NAME; \
movk PTR_REG (R), #:abs_g0_nc:NAME;
#else
# define MOVL(R, NAME) \
movz PTR_REG (R), #:abs_g1:NAME; \
movk PTR_REG (R), #:abs_g0_nc:NAME;
#endif
/* Since C identifiers are not normally prefixed with an underscore
on this system, the asm identifier `syscall_error' intrudes on the
C name space. Make sure we use an innocuous name. */
#define syscall_error __syscall_error
#define mcount _mcount
#endif /* __ASSEMBLER__ */
#endif /* _AARCH64_SYSDEP_H */
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