blob: 93d5010dfc92e78410f180d1aceb7c5b791b48ee [file] [log] [blame]
# SPDX-License-Identifier: GPL-2.0
#
# General architecture dependent options
#
#
# Note: arch/$(SRCARCH)/Kconfig needs to be included first so that it can
# override the default values in this file.
#
source "arch/$(SRCARCH)/Kconfig"
menu "General architecture-dependent options"
config ARCH_HAS_SUBPAGE_FAULTS
bool
help
Select if the architecture can check permissions at sub-page
granularity (e.g. arm64 MTE). The probe_user_*() functions
must be implemented.
config HOTPLUG_SMT
bool
config SMT_NUM_THREADS_DYNAMIC
bool
# Selected by HOTPLUG_CORE_SYNC_DEAD or HOTPLUG_CORE_SYNC_FULL
config HOTPLUG_CORE_SYNC
bool
# Basic CPU dead synchronization selected by architecture
config HOTPLUG_CORE_SYNC_DEAD
bool
select HOTPLUG_CORE_SYNC
# Full CPU synchronization with alive state selected by architecture
config HOTPLUG_CORE_SYNC_FULL
bool
select HOTPLUG_CORE_SYNC_DEAD if HOTPLUG_CPU
select HOTPLUG_CORE_SYNC
config HOTPLUG_SPLIT_STARTUP
bool
select HOTPLUG_CORE_SYNC_FULL
config HOTPLUG_PARALLEL
bool
select HOTPLUG_SPLIT_STARTUP
config GENERIC_ENTRY
bool
config KPROBES
bool "Kprobes"
depends on MODULES
depends on HAVE_KPROBES
select KALLSYMS
select NEED_TASKS_RCU
help
Kprobes allows you to trap at almost any kernel address and
execute a callback function. register_kprobe() establishes
a probepoint and specifies the callback. Kprobes is useful
for kernel debugging, non-intrusive instrumentation and testing.
If in doubt, say "N".
config JUMP_LABEL
bool "Optimize very unlikely/likely branches"
depends on HAVE_ARCH_JUMP_LABEL
select OBJTOOL if HAVE_JUMP_LABEL_HACK
help
This option enables a transparent branch optimization that
makes certain almost-always-true or almost-always-false branch
conditions even cheaper to execute within the kernel.
Certain performance-sensitive kernel code, such as trace points,
scheduler functionality, networking code and KVM have such
branches and include support for this optimization technique.
If it is detected that the compiler has support for "asm goto",
the kernel will compile such branches with just a nop
instruction. When the condition flag is toggled to true, the
nop will be converted to a jump instruction to execute the
conditional block of instructions.
This technique lowers overhead and stress on the branch prediction
of the processor and generally makes the kernel faster. The update
of the condition is slower, but those are always very rare.
( On 32-bit x86, the necessary options added to the compiler
flags may increase the size of the kernel slightly. )
config STATIC_KEYS_SELFTEST
bool "Static key selftest"
depends on JUMP_LABEL
help
Boot time self-test of the branch patching code.
config STATIC_CALL_SELFTEST
bool "Static call selftest"
depends on HAVE_STATIC_CALL
help
Boot time self-test of the call patching code.
config OPTPROBES
def_bool y
depends on KPROBES && HAVE_OPTPROBES
select NEED_TASKS_RCU
config KPROBES_ON_FTRACE
def_bool y
depends on KPROBES && HAVE_KPROBES_ON_FTRACE
depends on DYNAMIC_FTRACE_WITH_REGS
help
If function tracer is enabled and the arch supports full
passing of pt_regs to function tracing, then kprobes can
optimize on top of function tracing.
config UPROBES
def_bool n
depends on ARCH_SUPPORTS_UPROBES
help
Uprobes is the user-space counterpart to kprobes: they
enable instrumentation applications (such as 'perf probe')
to establish unintrusive probes in user-space binaries and
libraries, by executing handler functions when the probes
are hit by user-space applications.
( These probes come in the form of single-byte breakpoints,
managed by the kernel and kept transparent to the probed
application. )
config HAVE_64BIT_ALIGNED_ACCESS
def_bool 64BIT && !HAVE_EFFICIENT_UNALIGNED_ACCESS
help
Some architectures require 64 bit accesses to be 64 bit
aligned, which also requires structs containing 64 bit values
to be 64 bit aligned too. This includes some 32 bit
architectures which can do 64 bit accesses, as well as 64 bit
architectures without unaligned access.
This symbol should be selected by an architecture if 64 bit
accesses are required to be 64 bit aligned in this way even
though it is not a 64 bit architecture.
See Documentation/core-api/unaligned-memory-access.rst for
more information on the topic of unaligned memory accesses.
config HAVE_EFFICIENT_UNALIGNED_ACCESS
bool
help
Some architectures are unable to perform unaligned accesses
without the use of get_unaligned/put_unaligned. Others are
unable to perform such accesses efficiently (e.g. trap on
unaligned access and require fixing it up in the exception
handler.)
This symbol should be selected by an architecture if it can
perform unaligned accesses efficiently to allow different
code paths to be selected for these cases. Some network
drivers, for example, could opt to not fix up alignment
problems with received packets if doing so would not help
much.
See Documentation/core-api/unaligned-memory-access.rst for more
information on the topic of unaligned memory accesses.
config ARCH_USE_BUILTIN_BSWAP
bool
help
Modern versions of GCC (since 4.4) have builtin functions
for handling byte-swapping. Using these, instead of the old
inline assembler that the architecture code provides in the
__arch_bswapXX() macros, allows the compiler to see what's
happening and offers more opportunity for optimisation. In
particular, the compiler will be able to combine the byteswap
with a nearby load or store and use load-and-swap or
store-and-swap instructions if the architecture has them. It
should almost *never* result in code which is worse than the
hand-coded assembler in <asm/swab.h>. But just in case it
does, the use of the builtins is optional.
Any architecture with load-and-swap or store-and-swap
instructions should set this. And it shouldn't hurt to set it
on architectures that don't have such instructions.
config KRETPROBES
def_bool y
depends on KPROBES && (HAVE_KRETPROBES || HAVE_RETHOOK)
config KRETPROBE_ON_RETHOOK
def_bool y
depends on HAVE_RETHOOK
depends on KRETPROBES
select RETHOOK
config USER_RETURN_NOTIFIER
bool
depends on HAVE_USER_RETURN_NOTIFIER
help
Provide a kernel-internal notification when a cpu is about to
switch to user mode.
config HAVE_IOREMAP_PROT
bool
config HAVE_KPROBES
bool
config HAVE_KRETPROBES
bool
config HAVE_OPTPROBES
bool
config HAVE_KPROBES_ON_FTRACE
bool
config ARCH_CORRECT_STACKTRACE_ON_KRETPROBE
bool
help
Since kretprobes modifies return address on the stack, the
stacktrace may see the kretprobe trampoline address instead
of correct one. If the architecture stacktrace code and
unwinder can adjust such entries, select this configuration.
config HAVE_FUNCTION_ERROR_INJECTION
bool
config HAVE_NMI
bool
config HAVE_FUNCTION_DESCRIPTORS
bool
config TRACE_IRQFLAGS_SUPPORT
bool
config TRACE_IRQFLAGS_NMI_SUPPORT
bool
#
# An arch should select this if it provides all these things:
#
# task_pt_regs() in asm/processor.h or asm/ptrace.h
# arch_has_single_step() if there is hardware single-step support
# arch_has_block_step() if there is hardware block-step support
# asm/syscall.h supplying asm-generic/syscall.h interface
# linux/regset.h user_regset interfaces
# CORE_DUMP_USE_REGSET #define'd in linux/elf.h
# TIF_SYSCALL_TRACE calls ptrace_report_syscall_{entry,exit}
# TIF_NOTIFY_RESUME calls resume_user_mode_work()
#
config HAVE_ARCH_TRACEHOOK
bool
config HAVE_DMA_CONTIGUOUS
bool
config GENERIC_SMP_IDLE_THREAD
bool
config GENERIC_IDLE_POLL_SETUP
bool
config ARCH_HAS_FORTIFY_SOURCE
bool
help
An architecture should select this when it can successfully
build and run with CONFIG_FORTIFY_SOURCE.
#
# Select if the arch provides a historic keepinit alias for the retain_initrd
# command line option
#
config ARCH_HAS_KEEPINITRD
bool
# Select if arch has all set_memory_ro/rw/x/nx() functions in asm/cacheflush.h
config ARCH_HAS_SET_MEMORY
bool
# Select if arch has all set_direct_map_invalid/default() functions
config ARCH_HAS_SET_DIRECT_MAP
bool
#
# Select if the architecture provides the arch_dma_set_uncached symbol to
# either provide an uncached segment alias for a DMA allocation, or
# to remap the page tables in place.
#
config ARCH_HAS_DMA_SET_UNCACHED
bool
#
# Select if the architectures provides the arch_dma_clear_uncached symbol
# to undo an in-place page table remap for uncached access.
#
config ARCH_HAS_DMA_CLEAR_UNCACHED
bool
config ARCH_HAS_CPU_FINALIZE_INIT
bool
# The architecture has a per-task state that includes the mm's PASID
config ARCH_HAS_CPU_PASID
bool
select IOMMU_MM_DATA
config HAVE_ARCH_THREAD_STRUCT_WHITELIST
bool
help
An architecture should select this to provide hardened usercopy
knowledge about what region of the thread_struct should be
whitelisted for copying to userspace. Normally this is only the
FPU registers. Specifically, arch_thread_struct_whitelist()
should be implemented. Without this, the entire thread_struct
field in task_struct will be left whitelisted.
# Select if arch wants to size task_struct dynamically via arch_task_struct_size:
config ARCH_WANTS_DYNAMIC_TASK_STRUCT
bool
config ARCH_WANTS_NO_INSTR
bool
help
An architecture should select this if the noinstr macro is being used on
functions to denote that the toolchain should avoid instrumenting such
functions and is required for correctness.
config ARCH_32BIT_OFF_T
bool
depends on !64BIT
help
All new 32-bit architectures should have 64-bit off_t type on
userspace side which corresponds to the loff_t kernel type. This
is the requirement for modern ABIs. Some existing architectures
still support 32-bit off_t. This option is enabled for all such
architectures explicitly.
# Selected by 64 bit architectures which have a 32 bit f_tinode in struct ustat
config ARCH_32BIT_USTAT_F_TINODE
bool
config HAVE_ASM_MODVERSIONS
bool
help
This symbol should be selected by an architecture if it provides
<asm/asm-prototypes.h> to support the module versioning for symbols
exported from assembly code.
config HAVE_REGS_AND_STACK_ACCESS_API
bool
help
This symbol should be selected by an architecture if it supports
the API needed to access registers and stack entries from pt_regs,
declared in asm/ptrace.h
For example the kprobes-based event tracer needs this API.
config HAVE_RSEQ
bool
depends on HAVE_REGS_AND_STACK_ACCESS_API
help
This symbol should be selected by an architecture if it
supports an implementation of restartable sequences.
config HAVE_RUST
bool
help
This symbol should be selected by an architecture if it
supports Rust.
config HAVE_FUNCTION_ARG_ACCESS_API
bool
help
This symbol should be selected by an architecture if it supports
the API needed to access function arguments from pt_regs,
declared in asm/ptrace.h
config HAVE_HW_BREAKPOINT
bool
depends on PERF_EVENTS
config HAVE_MIXED_BREAKPOINTS_REGS
bool
depends on HAVE_HW_BREAKPOINT
help
Depending on the arch implementation of hardware breakpoints,
some of them have separate registers for data and instruction
breakpoints addresses, others have mixed registers to store
them but define the access type in a control register.
Select this option if your arch implements breakpoints under the
latter fashion.
config HAVE_USER_RETURN_NOTIFIER
bool
config HAVE_PERF_EVENTS_NMI
bool
help
System hardware can generate an NMI using the perf event
subsystem. Also has support for calculating CPU cycle events
to determine how many clock cycles in a given period.
config HAVE_HARDLOCKUP_DETECTOR_PERF
bool
depends on HAVE_PERF_EVENTS_NMI
help
The arch chooses to use the generic perf-NMI-based hardlockup
detector. Must define HAVE_PERF_EVENTS_NMI.
config HAVE_HARDLOCKUP_DETECTOR_ARCH
bool
help
The arch provides its own hardlockup detector implementation instead
of the generic ones.
It uses the same command line parameters, and sysctl interface,
as the generic hardlockup detectors.
config HAVE_PERF_REGS
bool
help
Support selective register dumps for perf events. This includes
bit-mapping of each registers and a unique architecture id.
config HAVE_PERF_USER_STACK_DUMP
bool
help
Support user stack dumps for perf event samples. This needs
access to the user stack pointer which is not unified across
architectures.
config HAVE_ARCH_JUMP_LABEL
bool
config HAVE_ARCH_JUMP_LABEL_RELATIVE
bool
config MMU_GATHER_TABLE_FREE
bool
config MMU_GATHER_RCU_TABLE_FREE
bool
select MMU_GATHER_TABLE_FREE
config MMU_GATHER_PAGE_SIZE
bool
config MMU_GATHER_NO_RANGE
bool
select MMU_GATHER_MERGE_VMAS
config MMU_GATHER_NO_FLUSH_CACHE
bool
config MMU_GATHER_MERGE_VMAS
bool
config MMU_GATHER_NO_GATHER
bool
depends on MMU_GATHER_TABLE_FREE
config ARCH_WANT_IRQS_OFF_ACTIVATE_MM
bool
help
Temporary select until all architectures can be converted to have
irqs disabled over activate_mm. Architectures that do IPI based TLB
shootdowns should enable this.
# Use normal mm refcounting for MMU_LAZY_TLB kernel thread references.
# MMU_LAZY_TLB_REFCOUNT=n can improve the scalability of context switching
# to/from kernel threads when the same mm is running on a lot of CPUs (a large
# multi-threaded application), by reducing contention on the mm refcount.
#
# This can be disabled if the architecture ensures no CPUs are using an mm as a
# "lazy tlb" beyond its final refcount (i.e., by the time __mmdrop frees the mm
# or its kernel page tables). This could be arranged by arch_exit_mmap(), or
# final exit(2) TLB flush, for example.
#
# To implement this, an arch *must*:
# Ensure the _lazy_tlb variants of mmgrab/mmdrop are used when manipulating
# the lazy tlb reference of a kthread's ->active_mm (non-arch code has been
# converted already).
config MMU_LAZY_TLB_REFCOUNT
def_bool y
depends on !MMU_LAZY_TLB_SHOOTDOWN
# This option allows MMU_LAZY_TLB_REFCOUNT=n. It ensures no CPUs are using an
# mm as a lazy tlb beyond its last reference count, by shooting down these
# users before the mm is deallocated. __mmdrop() first IPIs all CPUs that may
# be using the mm as a lazy tlb, so that they may switch themselves to using
# init_mm for their active mm. mm_cpumask(mm) is used to determine which CPUs
# may be using mm as a lazy tlb mm.
#
# To implement this, an arch *must*:
# - At the time of the final mmdrop of the mm, ensure mm_cpumask(mm) contains
# at least all possible CPUs in which the mm is lazy.
# - It must meet the requirements for MMU_LAZY_TLB_REFCOUNT=n (see above).
config MMU_LAZY_TLB_SHOOTDOWN
bool
config ARCH_HAVE_NMI_SAFE_CMPXCHG
bool
config ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
bool
config HAVE_ALIGNED_STRUCT_PAGE
bool
help
This makes sure that struct pages are double word aligned and that
e.g. the SLUB allocator can perform double word atomic operations
on a struct page for better performance. However selecting this
might increase the size of a struct page by a word.
config HAVE_CMPXCHG_LOCAL
bool
config HAVE_CMPXCHG_DOUBLE
bool
config ARCH_WEAK_RELEASE_ACQUIRE
bool
config ARCH_WANT_IPC_PARSE_VERSION
bool
config ARCH_WANT_COMPAT_IPC_PARSE_VERSION
bool
config ARCH_WANT_OLD_COMPAT_IPC
select ARCH_WANT_COMPAT_IPC_PARSE_VERSION
bool
config HAVE_ARCH_SECCOMP
bool
help
An arch should select this symbol to support seccomp mode 1 (the fixed
syscall policy), and must provide an overrides for __NR_seccomp_sigreturn,
and compat syscalls if the asm-generic/seccomp.h defaults need adjustment:
- __NR_seccomp_read_32
- __NR_seccomp_write_32
- __NR_seccomp_exit_32
- __NR_seccomp_sigreturn_32
config HAVE_ARCH_SECCOMP_FILTER
bool
select HAVE_ARCH_SECCOMP
help
An arch should select this symbol if it provides all of these things:
- all the requirements for HAVE_ARCH_SECCOMP
- syscall_get_arch()
- syscall_get_arguments()
- syscall_rollback()
- syscall_set_return_value()
- SIGSYS siginfo_t support
- secure_computing is called from a ptrace_event()-safe context
- secure_computing return value is checked and a return value of -1
results in the system call being skipped immediately.
- seccomp syscall wired up
- if !HAVE_SPARSE_SYSCALL_NR, have SECCOMP_ARCH_NATIVE,
SECCOMP_ARCH_NATIVE_NR, SECCOMP_ARCH_NATIVE_NAME defined. If
COMPAT is supported, have the SECCOMP_ARCH_COMPAT* defines too.
config SECCOMP
prompt "Enable seccomp to safely execute untrusted bytecode"
def_bool y
depends on HAVE_ARCH_SECCOMP
help
This kernel feature is useful for number crunching applications
that may need to handle untrusted bytecode during their
execution. By using pipes or other transports made available
to the process as file descriptors supporting the read/write
syscalls, it's possible to isolate those applications in their
own address space using seccomp. Once seccomp is enabled via
prctl(PR_SET_SECCOMP) or the seccomp() syscall, it cannot be
disabled and the task is only allowed to execute a few safe
syscalls defined by each seccomp mode.
If unsure, say Y.
config SECCOMP_FILTER
def_bool y
depends on HAVE_ARCH_SECCOMP_FILTER && SECCOMP && NET
help
Enable tasks to build secure computing environments defined
in terms of Berkeley Packet Filter programs which implement
task-defined system call filtering polices.
See Documentation/userspace-api/seccomp_filter.rst for details.
config SECCOMP_CACHE_DEBUG
bool "Show seccomp filter cache status in /proc/pid/seccomp_cache"
depends on SECCOMP_FILTER && !HAVE_SPARSE_SYSCALL_NR
depends on PROC_FS
help
This enables the /proc/pid/seccomp_cache interface to monitor
seccomp cache data. The file format is subject to change. Reading
the file requires CAP_SYS_ADMIN.
This option is for debugging only. Enabling presents the risk that
an adversary may be able to infer the seccomp filter logic.
If unsure, say N.
config HAVE_ARCH_STACKLEAK
bool
help
An architecture should select this if it has the code which
fills the used part of the kernel stack with the STACKLEAK_POISON
value before returning from system calls.
config HAVE_STACKPROTECTOR
bool
help
An arch should select this symbol if:
- it has implemented a stack canary (e.g. __stack_chk_guard)
config STACKPROTECTOR
bool "Stack Protector buffer overflow detection"
depends on HAVE_STACKPROTECTOR
depends on $(cc-option,-fstack-protector)
default y
help
This option turns on the "stack-protector" GCC feature. This
feature puts, at the beginning of functions, a canary value on
the stack just before the return address, and validates
the value just before actually returning. Stack based buffer
overflows (that need to overwrite this return address) now also
overwrite the canary, which gets detected and the attack is then
neutralized via a kernel panic.
Functions will have the stack-protector canary logic added if they
have an 8-byte or larger character array on the stack.
This feature requires gcc version 4.2 or above, or a distribution
gcc with the feature backported ("-fstack-protector").
On an x86 "defconfig" build, this feature adds canary checks to
about 3% of all kernel functions, which increases kernel code size
by about 0.3%.
config STACKPROTECTOR_STRONG
bool "Strong Stack Protector"
depends on STACKPROTECTOR
depends on $(cc-option,-fstack-protector-strong)
default y
help
Functions will have the stack-protector canary logic added in any
of the following conditions:
- local variable's address used as part of the right hand side of an
assignment or function argument
- local variable is an array (or union containing an array),
regardless of array type or length
- uses register local variables
This feature requires gcc version 4.9 or above, or a distribution
gcc with the feature backported ("-fstack-protector-strong").
On an x86 "defconfig" build, this feature adds canary checks to
about 20% of all kernel functions, which increases the kernel code
size by about 2%.
config ARCH_SUPPORTS_SHADOW_CALL_STACK
bool
help
An architecture should select this if it supports the compiler's
Shadow Call Stack and implements runtime support for shadow stack
switching.
config SHADOW_CALL_STACK
bool "Shadow Call Stack"
depends on ARCH_SUPPORTS_SHADOW_CALL_STACK
depends on DYNAMIC_FTRACE_WITH_ARGS || DYNAMIC_FTRACE_WITH_REGS || !FUNCTION_GRAPH_TRACER
depends on MMU
help
This option enables the compiler's Shadow Call Stack, which
uses a shadow stack to protect function return addresses from
being overwritten by an attacker. More information can be found
in the compiler's documentation:
- Clang: https://clang.llvm.org/docs/ShadowCallStack.html
- GCC: https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#Instrumentation-Options
Note that security guarantees in the kernel differ from the
ones documented for user space. The kernel must store addresses
of shadow stacks in memory, which means an attacker capable of
reading and writing arbitrary memory may be able to locate them
and hijack control flow by modifying the stacks.
config DYNAMIC_SCS
bool
help
Set by the arch code if it relies on code patching to insert the
shadow call stack push and pop instructions rather than on the
compiler.
config LTO
bool
help
Selected if the kernel will be built using the compiler's LTO feature.
config LTO_CLANG
bool
select LTO
help
Selected if the kernel will be built using Clang's LTO feature.
config ARCH_SUPPORTS_LTO_CLANG
bool
help
An architecture should select this option if it supports:
- compiling with Clang,
- compiling inline assembly with Clang's integrated assembler,
- and linking with LLD.
config ARCH_SUPPORTS_LTO_CLANG_THIN
bool
help
An architecture should select this option if it can support Clang's
ThinLTO mode.
config HAS_LTO_CLANG
def_bool y
depends on CC_IS_CLANG && LD_IS_LLD && AS_IS_LLVM
depends on $(success,$(NM) --help | head -n 1 | grep -qi llvm)
depends on $(success,$(AR) --help | head -n 1 | grep -qi llvm)
depends on ARCH_SUPPORTS_LTO_CLANG
depends on !FTRACE_MCOUNT_USE_RECORDMCOUNT
# https://github.com/ClangBuiltLinux/linux/issues/1721
depends on (!KASAN || KASAN_HW_TAGS || CLANG_VERSION >= 170000) || !DEBUG_INFO
depends on (!KCOV || CLANG_VERSION >= 170000) || !DEBUG_INFO
depends on !GCOV_KERNEL
help
The compiler and Kconfig options support building with Clang's
LTO.
choice
prompt "Link Time Optimization (LTO)"
default LTO_NONE
help
This option enables Link Time Optimization (LTO), which allows the
compiler to optimize binaries globally.
If unsure, select LTO_NONE. Note that LTO is very resource-intensive
so it's disabled by default.
config LTO_NONE
bool "None"
help
Build the kernel normally, without Link Time Optimization (LTO).
config LTO_CLANG_FULL
bool "Clang Full LTO (EXPERIMENTAL)"
depends on HAS_LTO_CLANG
depends on !COMPILE_TEST
select LTO_CLANG
help
This option enables Clang's full Link Time Optimization (LTO), which
allows the compiler to optimize the kernel globally. If you enable
this option, the compiler generates LLVM bitcode instead of ELF
object files, and the actual compilation from bitcode happens at
the LTO link step, which may take several minutes depending on the
kernel configuration. More information can be found from LLVM's
documentation:
https://llvm.org/docs/LinkTimeOptimization.html
During link time, this option can use a large amount of RAM, and
may take much longer than the ThinLTO option.
config LTO_CLANG_THIN
bool "Clang ThinLTO (EXPERIMENTAL)"
depends on HAS_LTO_CLANG && ARCH_SUPPORTS_LTO_CLANG_THIN
select LTO_CLANG
help
This option enables Clang's ThinLTO, which allows for parallel
optimization and faster incremental compiles compared to the
CONFIG_LTO_CLANG_FULL option. More information can be found
from Clang's documentation:
https://clang.llvm.org/docs/ThinLTO.html
If unsure, say Y.
endchoice
config ARCH_SUPPORTS_CFI_CLANG
bool
help
An architecture should select this option if it can support Clang's
Control-Flow Integrity (CFI) checking.
config ARCH_USES_CFI_TRAPS
bool
config CFI_CLANG
bool "Use Clang's Control Flow Integrity (CFI)"
depends on ARCH_SUPPORTS_CFI_CLANG
depends on $(cc-option,-fsanitize=kcfi)
help
This option enables Clang's forward-edge Control Flow Integrity
(CFI) checking, where the compiler injects a runtime check to each
indirect function call to ensure the target is a valid function with
the correct static type. This restricts possible call targets and
makes it more difficult for an attacker to exploit bugs that allow
the modification of stored function pointers. More information can be
found from Clang's documentation:
https://clang.llvm.org/docs/ControlFlowIntegrity.html
config CFI_PERMISSIVE
bool "Use CFI in permissive mode"
depends on CFI_CLANG
help
When selected, Control Flow Integrity (CFI) violations result in a
warning instead of a kernel panic. This option should only be used
for finding indirect call type mismatches during development.
If unsure, say N.
config HAVE_ARCH_WITHIN_STACK_FRAMES
bool
help
An architecture should select this if it can walk the kernel stack
frames to determine if an object is part of either the arguments
or local variables (i.e. that it excludes saved return addresses,
and similar) by implementing an inline arch_within_stack_frames(),
which is used by CONFIG_HARDENED_USERCOPY.
config HAVE_CONTEXT_TRACKING_USER
bool
help
Provide kernel/user boundaries probes necessary for subsystems
that need it, such as userspace RCU extended quiescent state.
Syscalls need to be wrapped inside user_exit()-user_enter(), either
optimized behind static key or through the slow path using TIF_NOHZ
flag. Exceptions handlers must be wrapped as well. Irqs are already
protected inside ct_irq_enter/ct_irq_exit() but preemption or signal
handling on irq exit still need to be protected.
config HAVE_CONTEXT_TRACKING_USER_OFFSTACK
bool
help
Architecture neither relies on exception_enter()/exception_exit()
nor on schedule_user(). Also preempt_schedule_notrace() and
preempt_schedule_irq() can't be called in a preemptible section
while context tracking is CONTEXT_USER. This feature reflects a sane
entry implementation where the following requirements are met on
critical entry code, ie: before user_exit() or after user_enter():
- Critical entry code isn't preemptible (or better yet:
not interruptible).
- No use of RCU read side critical sections, unless ct_nmi_enter()
got called.
- No use of instrumentation, unless instrumentation_begin() got
called.
config HAVE_TIF_NOHZ
bool
help
Arch relies on TIF_NOHZ and syscall slow path to implement context
tracking calls to user_enter()/user_exit().
config HAVE_VIRT_CPU_ACCOUNTING
bool
config HAVE_VIRT_CPU_ACCOUNTING_IDLE
bool
help
Architecture has its own way to account idle CPU time and therefore
doesn't implement vtime_account_idle().
config ARCH_HAS_SCALED_CPUTIME
bool
config HAVE_VIRT_CPU_ACCOUNTING_GEN
bool
default y if 64BIT
help
With VIRT_CPU_ACCOUNTING_GEN, cputime_t becomes 64-bit.
Before enabling this option, arch code must be audited
to ensure there are no races in concurrent read/write of
cputime_t. For example, reading/writing 64-bit cputime_t on
some 32-bit arches may require multiple accesses, so proper
locking is needed to protect against concurrent accesses.
config HAVE_IRQ_TIME_ACCOUNTING
bool
help
Archs need to ensure they use a high enough resolution clock to
support irq time accounting and then call enable_sched_clock_irqtime().
config HAVE_MOVE_PUD
bool
help
Architectures that select this are able to move page tables at the
PUD level. If there are only 3 page table levels, the move effectively
happens at the PGD level.
config HAVE_MOVE_PMD
bool
help
Archs that select this are able to move page tables at the PMD level.
config HAVE_ARCH_TRANSPARENT_HUGEPAGE
bool
config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
bool
config HAVE_ARCH_HUGE_VMAP
bool
#
# Archs that select this would be capable of PMD-sized vmaps (i.e.,
# arch_vmap_pmd_supported() returns true). The VM_ALLOW_HUGE_VMAP flag
# must be used to enable allocations to use hugepages.
#
config HAVE_ARCH_HUGE_VMALLOC
depends on HAVE_ARCH_HUGE_VMAP
bool
config ARCH_WANT_HUGE_PMD_SHARE
bool
# Archs that want to use pmd_mkwrite on kernel memory need it defined even
# if there are no userspace memory management features that use it
config ARCH_WANT_KERNEL_PMD_MKWRITE
bool
config ARCH_WANT_PMD_MKWRITE
def_bool TRANSPARENT_HUGEPAGE || ARCH_WANT_KERNEL_PMD_MKWRITE
config HAVE_ARCH_SOFT_DIRTY
bool
config HAVE_MOD_ARCH_SPECIFIC
bool
help
The arch uses struct mod_arch_specific to store data. Many arches
just need a simple module loader without arch specific data - those
should not enable this.
config MODULES_USE_ELF_RELA
bool
help
Modules only use ELF RELA relocations. Modules with ELF REL
relocations will give an error.
config MODULES_USE_ELF_REL
bool
help
Modules only use ELF REL relocations. Modules with ELF RELA
relocations will give an error.
config ARCH_WANTS_MODULES_DATA_IN_VMALLOC
bool
help
For architectures like powerpc/32 which have constraints on module
allocation and need to allocate module data outside of module area.
config HAVE_IRQ_EXIT_ON_IRQ_STACK
bool
help
Architecture doesn't only execute the irq handler on the irq stack
but also irq_exit(). This way we can process softirqs on this irq
stack instead of switching to a new one when we call __do_softirq()
in the end of an hardirq.
This spares a stack switch and improves cache usage on softirq
processing.
config HAVE_SOFTIRQ_ON_OWN_STACK
bool
help
Architecture provides a function to run __do_softirq() on a
separate stack.
config SOFTIRQ_ON_OWN_STACK
def_bool HAVE_SOFTIRQ_ON_OWN_STACK && !PREEMPT_RT
config ALTERNATE_USER_ADDRESS_SPACE
bool
help
Architectures set this when the CPU uses separate address
spaces for kernel and user space pointers. In this case, the
access_ok() check on a __user pointer is skipped.
config PGTABLE_LEVELS
int
default 2
config ARCH_HAS_ELF_RANDOMIZE
bool
help
An architecture supports choosing randomized locations for
stack, mmap, brk, and ET_DYN. Defined functions:
- arch_mmap_rnd()
- arch_randomize_brk()
config HAVE_ARCH_MMAP_RND_BITS
bool
help
An arch should select this symbol if it supports setting a variable
number of bits for use in establishing the base address for mmap
allocations, has MMU enabled and provides values for both:
- ARCH_MMAP_RND_BITS_MIN
- ARCH_MMAP_RND_BITS_MAX
config HAVE_EXIT_THREAD
bool
help
An architecture implements exit_thread.
config ARCH_MMAP_RND_BITS_MIN
int
config ARCH_MMAP_RND_BITS_MAX
int
config ARCH_MMAP_RND_BITS_DEFAULT
int
config ARCH_MMAP_RND_BITS
int "Number of bits to use for ASLR of mmap base address" if EXPERT
range ARCH_MMAP_RND_BITS_MIN ARCH_MMAP_RND_BITS_MAX
default ARCH_MMAP_RND_BITS_DEFAULT if ARCH_MMAP_RND_BITS_DEFAULT
default ARCH_MMAP_RND_BITS_MIN
depends on HAVE_ARCH_MMAP_RND_BITS
help
This value can be used to select the number of bits to use to
determine the random offset to the base address of vma regions
resulting from mmap allocations. This value will be bounded
by the architecture's minimum and maximum supported values.
This value can be changed after boot using the
/proc/sys/vm/mmap_rnd_bits tunable
config HAVE_ARCH_MMAP_RND_COMPAT_BITS
bool
help
An arch should select this symbol if it supports running applications
in compatibility mode, supports setting a variable number of bits for
use in establishing the base address for mmap allocations, has MMU
enabled and provides values for both:
- ARCH_MMAP_RND_COMPAT_BITS_MIN
- ARCH_MMAP_RND_COMPAT_BITS_MAX
config ARCH_MMAP_RND_COMPAT_BITS_MIN
int
config ARCH_MMAP_RND_COMPAT_BITS_MAX
int
config ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
int
config ARCH_MMAP_RND_COMPAT_BITS
int "Number of bits to use for ASLR of mmap base address for compatible applications" if EXPERT
range ARCH_MMAP_RND_COMPAT_BITS_MIN ARCH_MMAP_RND_COMPAT_BITS_MAX
default ARCH_MMAP_RND_COMPAT_BITS_DEFAULT if ARCH_MMAP_RND_COMPAT_BITS_DEFAULT
default ARCH_MMAP_RND_COMPAT_BITS_MIN
depends on HAVE_ARCH_MMAP_RND_COMPAT_BITS
help
This value can be used to select the number of bits to use to
determine the random offset to the base address of vma regions
resulting from mmap allocations for compatible applications This
value will be bounded by the architecture's minimum and maximum
supported values.
This value can be changed after boot using the
/proc/sys/vm/mmap_rnd_compat_bits tunable
config HAVE_ARCH_COMPAT_MMAP_BASES
bool
help
This allows 64bit applications to invoke 32-bit mmap() syscall
and vice-versa 32-bit applications to call 64-bit mmap().
Required for applications doing different bitness syscalls.
config HAVE_PAGE_SIZE_4KB
bool
config HAVE_PAGE_SIZE_8KB
bool
config HAVE_PAGE_SIZE_16KB
bool
config HAVE_PAGE_SIZE_32KB
bool
config HAVE_PAGE_SIZE_64KB
bool
config HAVE_PAGE_SIZE_256KB
bool
choice
prompt "MMU page size"
config PAGE_SIZE_4KB
bool "4KiB pages"
depends on HAVE_PAGE_SIZE_4KB
help
This option select the standard 4KiB Linux page size and the only
available option on many architectures. Using 4KiB page size will
minimize memory consumption and is therefore recommended for low
memory systems.
Some software that is written for x86 systems makes incorrect
assumptions about the page size and only runs on 4KiB pages.
config PAGE_SIZE_8KB
bool "8KiB pages"
depends on HAVE_PAGE_SIZE_8KB
help
This option is the only supported page size on a few older
processors, and can be slightly faster than 4KiB pages.
config PAGE_SIZE_16KB
bool "16KiB pages"
depends on HAVE_PAGE_SIZE_16KB
help
This option is usually a good compromise between memory
consumption and performance for typical desktop and server
workloads, often saving a level of page table lookups compared
to 4KB pages as well as reducing TLB pressure and overhead of
per-page operations in the kernel at the expense of a larger
page cache.
config PAGE_SIZE_32KB
bool "32KiB pages"
depends on HAVE_PAGE_SIZE_32KB
help
Using 32KiB page size will result in slightly higher performance
kernel at the price of higher memory consumption compared to
16KiB pages. This option is available only on cnMIPS cores.
Note that you will need a suitable Linux distribution to
support this.
config PAGE_SIZE_64KB
bool "64KiB pages"
depends on HAVE_PAGE_SIZE_64KB
help
Using 64KiB page size will result in slightly higher performance
kernel at the price of much higher memory consumption compared to
4KiB or 16KiB pages.
This is not suitable for general-purpose workloads but the
better performance may be worth the cost for certain types of
supercomputing or database applications that work mostly with
large in-memory data rather than small files.
config PAGE_SIZE_256KB
bool "256KiB pages"
depends on HAVE_PAGE_SIZE_256KB
help
256KiB pages have little practical value due to their extreme
memory usage. The kernel will only be able to run applications
that have been compiled with '-zmax-page-size' set to 256KiB
(the default is 64KiB or 4KiB on most architectures).
endchoice
config PAGE_SIZE_LESS_THAN_64KB
def_bool y
depends on !PAGE_SIZE_64KB
depends on PAGE_SIZE_LESS_THAN_256KB
config PAGE_SIZE_LESS_THAN_256KB
def_bool y
depends on !PAGE_SIZE_256KB
config PAGE_SHIFT
int
default 12 if PAGE_SIZE_4KB
default 13 if PAGE_SIZE_8KB
default 14 if PAGE_SIZE_16KB
default 15 if PAGE_SIZE_32KB
default 16 if PAGE_SIZE_64KB
default 18 if PAGE_SIZE_256KB
# This allows to use a set of generic functions to determine mmap base
# address by giving priority to top-down scheme only if the process
# is not in legacy mode (compat task, unlimited stack size or
# sysctl_legacy_va_layout).
# Architecture that selects this option can provide its own version of:
# - STACK_RND_MASK
config ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
bool
depends on MMU
select ARCH_HAS_ELF_RANDOMIZE
config HAVE_OBJTOOL
bool
config HAVE_JUMP_LABEL_HACK
bool
config HAVE_NOINSTR_HACK
bool
config HAVE_NOINSTR_VALIDATION
bool
config HAVE_UACCESS_VALIDATION
bool
select OBJTOOL
config HAVE_STACK_VALIDATION
bool
help
Architecture supports objtool compile-time frame pointer rule
validation.
config HAVE_RELIABLE_STACKTRACE
bool
help
Architecture has either save_stack_trace_tsk_reliable() or
arch_stack_walk_reliable() function which only returns a stack trace
if it can guarantee the trace is reliable.
config HAVE_ARCH_HASH
bool
default n
help
If this is set, the architecture provides an <asm/hash.h>
file which provides platform-specific implementations of some
functions in <linux/hash.h> or fs/namei.c.
config HAVE_ARCH_NVRAM_OPS
bool
config ISA_BUS_API
def_bool ISA
#
# ABI hall of shame
#
config CLONE_BACKWARDS
bool
help
Architecture has tls passed as the 4th argument of clone(2),
not the 5th one.
config CLONE_BACKWARDS2
bool
help
Architecture has the first two arguments of clone(2) swapped.
config CLONE_BACKWARDS3
bool
help
Architecture has tls passed as the 3rd argument of clone(2),
not the 5th one.
config ODD_RT_SIGACTION
bool
help
Architecture has unusual rt_sigaction(2) arguments
config OLD_SIGSUSPEND
bool
help
Architecture has old sigsuspend(2) syscall, of one-argument variety
config OLD_SIGSUSPEND3
bool
help
Even weirder antique ABI - three-argument sigsuspend(2)
config OLD_SIGACTION
bool
help
Architecture has old sigaction(2) syscall. Nope, not the same
as OLD_SIGSUSPEND | OLD_SIGSUSPEND3 - alpha has sigsuspend(2),
but fairly different variant of sigaction(2), thanks to OSF/1
compatibility...
config COMPAT_OLD_SIGACTION
bool
config COMPAT_32BIT_TIME
bool "Provide system calls for 32-bit time_t"
default !64BIT || COMPAT
help
This enables 32 bit time_t support in addition to 64 bit time_t support.
This is relevant on all 32-bit architectures, and 64-bit architectures
as part of compat syscall handling.
config ARCH_NO_PREEMPT
bool
config ARCH_SUPPORTS_RT
bool
config CPU_NO_EFFICIENT_FFS
def_bool n
config HAVE_ARCH_VMAP_STACK
def_bool n
help
An arch should select this symbol if it can support kernel stacks
in vmalloc space. This means:
- vmalloc space must be large enough to hold many kernel stacks.
This may rule out many 32-bit architectures.
- Stacks in vmalloc space need to work reliably. For example, if
vmap page tables are created on demand, either this mechanism
needs to work while the stack points to a virtual address with
unpopulated page tables or arch code (switch_to() and switch_mm(),
most likely) needs to ensure that the stack's page table entries
are populated before running on a possibly unpopulated stack.
- If the stack overflows into a guard page, something reasonable
should happen. The definition of "reasonable" is flexible, but
instantly rebooting without logging anything would be unfriendly.
config VMAP_STACK
default y
bool "Use a virtually-mapped stack"
depends on HAVE_ARCH_VMAP_STACK
depends on !KASAN || KASAN_HW_TAGS || KASAN_VMALLOC
help
Enable this if you want the use virtually-mapped kernel stacks
with guard pages. This causes kernel stack overflows to be
caught immediately rather than causing difficult-to-diagnose
corruption.
To use this with software KASAN modes, the architecture must support
backing virtual mappings with real shadow memory, and KASAN_VMALLOC
must be enabled.
config HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
def_bool n
help
An arch should select this symbol if it can support kernel stack
offset randomization with calls to add_random_kstack_offset()
during syscall entry and choose_random_kstack_offset() during
syscall exit. Careful removal of -fstack-protector-strong and
-fstack-protector should also be applied to the entry code and
closely examined, as the artificial stack bump looks like an array
to the compiler, so it will attempt to add canary checks regardless
of the static branch state.
config RANDOMIZE_KSTACK_OFFSET
bool "Support for randomizing kernel stack offset on syscall entry" if EXPERT
default y
depends on HAVE_ARCH_RANDOMIZE_KSTACK_OFFSET
depends on INIT_STACK_NONE || !CC_IS_CLANG || CLANG_VERSION >= 140000
help
The kernel stack offset can be randomized (after pt_regs) by
roughly 5 bits of entropy, frustrating memory corruption
attacks that depend on stack address determinism or
cross-syscall address exposures.
The feature is controlled via the "randomize_kstack_offset=on/off"
kernel boot param, and if turned off has zero overhead due to its use
of static branches (see JUMP_LABEL).
If unsure, say Y.
config RANDOMIZE_KSTACK_OFFSET_DEFAULT
bool "Default state of kernel stack offset randomization"
depends on RANDOMIZE_KSTACK_OFFSET
help
Kernel stack offset randomization is controlled by kernel boot param
"randomize_kstack_offset=on/off", and this config chooses the default
boot state.
config ARCH_OPTIONAL_KERNEL_RWX
def_bool n
config ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
def_bool n
config ARCH_HAS_STRICT_KERNEL_RWX
def_bool n
config STRICT_KERNEL_RWX
bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX
depends on ARCH_HAS_STRICT_KERNEL_RWX
default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
help
If this is set, kernel text and rodata memory will be made read-only,
and non-text memory will be made non-executable. This provides
protection against certain security exploits (e.g. executing the heap
or modifying text)
These features are considered standard security practice these days.
You should say Y here in almost all cases.
config ARCH_HAS_STRICT_MODULE_RWX
def_bool n
config STRICT_MODULE_RWX
bool "Set loadable kernel module data as NX and text as RO" if ARCH_OPTIONAL_KERNEL_RWX
depends on ARCH_HAS_STRICT_MODULE_RWX && MODULES
default !ARCH_OPTIONAL_KERNEL_RWX || ARCH_OPTIONAL_KERNEL_RWX_DEFAULT
help
If this is set, module text and rodata memory will be made read-only,
and non-text memory will be made non-executable. This provides
protection against certain security exploits (e.g. writing to text)
# select if the architecture provides an asm/dma-direct.h header
config ARCH_HAS_PHYS_TO_DMA
bool
config HAVE_ARCH_COMPILER_H
bool
help
An architecture can select this if it provides an
asm/compiler.h header that should be included after
linux/compiler-*.h in order to override macro definitions that those
headers generally provide.
config HAVE_ARCH_PREL32_RELOCATIONS
bool
help
May be selected by an architecture if it supports place-relative
32-bit relocations, both in the toolchain and in the module loader,
in which case relative references can be used in special sections
for PCI fixup, initcalls etc which are only half the size on 64 bit
architectures, and don't require runtime relocation on relocatable
kernels.
config ARCH_USE_MEMREMAP_PROT
bool
config LOCK_EVENT_COUNTS
bool "Locking event counts collection"
depends on DEBUG_FS
help
Enable light-weight counting of various locking related events
in the system with minimal performance impact. This reduces
the chance of application behavior change because of timing
differences. The counts are reported via debugfs.
# Select if the architecture has support for applying RELR relocations.
config ARCH_HAS_RELR
bool
config RELR
bool "Use RELR relocation packing"
depends on ARCH_HAS_RELR && TOOLS_SUPPORT_RELR
default y
help
Store the kernel's dynamic relocations in the RELR relocation packing
format. Requires a compatible linker (LLD supports this feature), as
well as compatible NM and OBJCOPY utilities (llvm-nm and llvm-objcopy
are compatible).
config ARCH_HAS_MEM_ENCRYPT
bool
config ARCH_HAS_CC_PLATFORM
bool
config HAVE_SPARSE_SYSCALL_NR
bool
help
An architecture should select this if its syscall numbering is sparse
to save space. For example, MIPS architecture has a syscall array with
entries at 4000, 5000 and 6000 locations. This option turns on syscall
related optimizations for a given architecture.
config ARCH_HAS_VDSO_DATA
bool
config HAVE_STATIC_CALL
bool
config HAVE_STATIC_CALL_INLINE
bool
depends on HAVE_STATIC_CALL
select OBJTOOL
config HAVE_PREEMPT_DYNAMIC
bool
config HAVE_PREEMPT_DYNAMIC_CALL
bool
depends on HAVE_STATIC_CALL
select HAVE_PREEMPT_DYNAMIC
help
An architecture should select this if it can handle the preemption
model being selected at boot time using static calls.
Where an architecture selects HAVE_STATIC_CALL_INLINE, any call to a
preemption function will be patched directly.
Where an architecture does not select HAVE_STATIC_CALL_INLINE, any
call to a preemption function will go through a trampoline, and the
trampoline will be patched.
It is strongly advised to support inline static call to avoid any
overhead.
config HAVE_PREEMPT_DYNAMIC_KEY
bool
depends on HAVE_ARCH_JUMP_LABEL
select HAVE_PREEMPT_DYNAMIC
help
An architecture should select this if it can handle the preemption
model being selected at boot time using static keys.
Each preemption function will be given an early return based on a
static key. This should have slightly lower overhead than non-inline
static calls, as this effectively inlines each trampoline into the
start of its callee. This may avoid redundant work, and may
integrate better with CFI schemes.
This will have greater overhead than using inline static calls as
the call to the preemption function cannot be entirely elided.
config ARCH_WANT_LD_ORPHAN_WARN
bool
help
An arch should select this symbol once all linker sections are explicitly
included, size-asserted, or discarded in the linker scripts. This is
important because we never want expected sections to be placed heuristically
by the linker, since the locations of such sections can change between linker
versions.
config HAVE_ARCH_PFN_VALID
bool
config ARCH_SUPPORTS_DEBUG_PAGEALLOC
bool
config ARCH_SUPPORTS_PAGE_TABLE_CHECK
bool
config ARCH_SPLIT_ARG64
bool
help
If a 32-bit architecture requires 64-bit arguments to be split into
pairs of 32-bit arguments, select this option.
config ARCH_HAS_ELFCORE_COMPAT
bool
config ARCH_HAS_PARANOID_L1D_FLUSH
bool
config ARCH_HAVE_TRACE_MMIO_ACCESS
bool
config DYNAMIC_SIGFRAME
bool
# Select, if arch has a named attribute group bound to NUMA device nodes.
config HAVE_ARCH_NODE_DEV_GROUP
bool
config ARCH_HAS_HW_PTE_YOUNG
bool
help
Architectures that select this option are capable of setting the
accessed bit in PTE entries when using them as part of linear address
translations. Architectures that require runtime check should select
this option and override arch_has_hw_pte_young().
config ARCH_HAS_NONLEAF_PMD_YOUNG
bool
help
Architectures that select this option are capable of setting the
accessed bit in non-leaf PMD entries when using them as part of linear
address translations. Page table walkers that clear the accessed bit
may use this capability to reduce their search space.
source "kernel/gcov/Kconfig"
source "scripts/gcc-plugins/Kconfig"
config FUNCTION_ALIGNMENT_4B
bool
config FUNCTION_ALIGNMENT_8B
bool
config FUNCTION_ALIGNMENT_16B
bool
config FUNCTION_ALIGNMENT_32B
bool
config FUNCTION_ALIGNMENT_64B
bool
config FUNCTION_ALIGNMENT
int
default 64 if FUNCTION_ALIGNMENT_64B
default 32 if FUNCTION_ALIGNMENT_32B
default 16 if FUNCTION_ALIGNMENT_16B
default 8 if FUNCTION_ALIGNMENT_8B
default 4 if FUNCTION_ALIGNMENT_4B
default 0
config CC_HAS_MIN_FUNCTION_ALIGNMENT
# Detect availability of the GCC option -fmin-function-alignment which
# guarantees minimal alignment for all functions, unlike
# -falign-functions which the compiler ignores for cold functions.
def_bool $(cc-option, -fmin-function-alignment=8)
config CC_HAS_SANE_FUNCTION_ALIGNMENT
# Set if the guaranteed alignment with -fmin-function-alignment is
# available or extra care is required in the kernel. Clang provides
# strict alignment always, even with -falign-functions.
def_bool CC_HAS_MIN_FUNCTION_ALIGNMENT || CC_IS_CLANG
config ARCH_NEED_CMPXCHG_1_EMU
bool
endmenu