man/man7/arch.7

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.Dd July 13, 2024
.Dt ARCH 7
.Os
.Sh NAME
.Nm arch
.Nd Architecture-specific details
.Sh DESCRIPTION
Differences between CPU architectures and platforms supported by
.Fx .
.Ss Introduction
This document is a quick reference of key ABI details of
.Fx
architecture ports.
For full details consult the processor-specific ABI supplement
documentation.
.Pp
If not explicitly mentioned, sizes are in bytes.
The architecture details in this document apply to
.Fx 12.0
and later, unless otherwise noted.
.Pp
.Fx
uses a flat address space.
Variables of types
.Vt unsigned long ,
.Vt uintptr_t ,
and
.Vt size_t
and pointers all have the same representation.
.Pp
In order to maximize compatibility with future pointer integrity mechanisms,
manipulations of pointers as integers should be performed via
.Vt uintptr_t
or
.Vt intptr_t
and no other types.
In particular,
.Vt long
and
.Vt ptrdiff_t
should be avoided.
.Pp
On some architectures, e.g.,
.Dv powerpc
and AIM variants of
.Dv powerpc64 ,
the kernel uses a separate address space.
On other architectures, kernel and a user mode process share a
single address space.
The kernel is located at the highest addresses.
.Pp
On each architecture, the main user mode thread's stack starts near
the highest user address and grows down.
.Pp
.Fx
architecture support varies by release.
This table shows currently supported CPU architectures along with the first
.Fx
release to support each architecture.
.Bl -column -offset indent "Architecture" "Initial Release"
.It Sy Architecture Ta Sy Initial Release
.It aarch64     Ta 11.0
.It amd64       Ta 5.1
.It armv7       Ta 12.0
.It i386        Ta 1.0
.It powerpc     Ta 6.0
.It powerpcspe  Ta 12.0
.It powerpc64   Ta 9.0
.It powerpc64le Ta 13.0
.It riscv64     Ta 12.0
.El
.Pp
Discontinued architectures are shown in the following table.
.Bl -column -offset indent "Architecture" "Initial Release" "Final Release"
.It Sy Architecture Ta Sy Initial Release Ta Sy Final Release
.It alpha       Ta 3.2   Ta 6.4
.It arm         Ta 6.0   Ta 12.4
.It armeb       Ta 8.0   Ta 11.4
.It armv6       Ta 10.0  Ta 14.x
.It ia64        Ta 5.0   Ta 10.4
.It mips        Ta 8.0   Ta 13.x
.It mipsel      Ta 9.0   Ta 13.x
.It mipselhf    Ta 12.0  Ta 13.x
.It mipshf      Ta 12.0  Ta 13.x
.It mipsn32     Ta 9.0   Ta 13.x
.It mips64      Ta 9.0   Ta 13.x
.It mips64el    Ta 9.0   Ta 13.x
.It mips64elhf  Ta 12.0  Ta 13.x
.It mips64hf    Ta 12.0  Ta 13.x
.It pc98        Ta 2.2   Ta 11.4
.It riscv64sf   Ta 12.0  Ta 13.x
.It sparc64     Ta 5.0   Ta 12.4
.El
.Ss Type sizes
All
.Fx
architectures use some variant of the ELF (see
.Xr elf 5 )
.Sy Application Binary Interface
(ABI) for the machine processor.
All supported ABIs can be divided into two groups:
.Bl -tag -width "Dv ILP32"
.It Dv ILP32
.Vt int ,
.Vt long ,
.Vt void *
types machine representations all have 4-byte size.
.It Dv LP64
.Vt int
type machine representation uses 4 bytes,
while
.Vt long
and
.Vt void *
are 8 bytes.
.El
.Pp
Some machines support more than one
.Fx
ABI.
Typically these are 64-bit machines, where the
.Dq native
.Dv LP64
execution environment is accompanied by the
.Dq legacy
.Dv ILP32
environment, which was the historical 32-bit predecessor for 64-bit evolution.
Examples are:
.Bl -column -offset indent "powerpc64" "ILP32 counterpart"
.It Sy LP64        Ta Sy ILP32 counterpart
.It Dv amd64       Ta Dv i386
.It Dv powerpc64   Ta Dv powerpc
.It Dv aarch64     Ta Dv armv7
.El
.Pp
.Dv aarch64
will support execution of
.Dv armv7
binaries if the CPU implements
.Dv AArch32
execution state, however older arm binaries are not supported by
.Fx .
.Pp
On all supported architectures:
.Bl -column -offset indent "long long" "Size"
.It Sy Type Ta Sy Size
.It short Ta 2
.It int Ta 4
.It long Ta sizeof(void*)
.It long long Ta 8
.It float Ta 4
.It double Ta 8
.El
.Pp
Integers are represented in two's complement.
Alignment of integer and pointer types is natural, that is,
the address of the variable must be congruent to zero modulo the type size.
Most ILP32 ABIs, except
.Dv arm ,
require only 4-byte alignment for 64-bit integers.
.Pp
Machine-dependent type sizes:
.Bl -column -offset indent "Architecture" "void *" "long double" "time_t"
.It Sy Architecture Ta Sy void * Ta Sy long double Ta Sy time_t
.It aarch64     Ta 8 Ta 16 Ta 8
.It amd64       Ta 8 Ta 16 Ta 8
.It armv7       Ta 4 Ta  8 Ta 8
.It i386        Ta 4 Ta 12 Ta 4
.It powerpc     Ta 4 Ta  8 Ta 8
.It powerpcspe  Ta 4 Ta  8 Ta 8
.It powerpc64   Ta 8 Ta  8 Ta 8
.It powerpc64le Ta 8 Ta  8 Ta 8
.It riscv64     Ta 8 Ta 16 Ta 8
.El
.Pp
.Sy time_t
is 8 bytes on all supported architectures except i386.
.Ss Endianness and Char Signedness
.Bl -column -offset indent "Architecture" "Endianness" "char Signedness"
.It Sy Architecture Ta Sy Endianness Ta Sy char Signedness
.It aarch64     Ta little Ta unsigned
.It amd64       Ta little Ta   signed
.It armv7       Ta little Ta unsigned
.It i386        Ta little Ta   signed
.It powerpc     Ta big    Ta unsigned
.It powerpcspe  Ta big    Ta unsigned
.It powerpc64   Ta big    Ta unsigned
.It powerpc64le Ta little Ta unsigned
.It riscv64     Ta little Ta   signed
.El
.Ss Page Size
.Bl -column -offset indent "Architecture" "Page Sizes"
.It Sy Architecture Ta Sy Page Sizes
.It aarch64     Ta 4K, 64K, 2M, 1G
.It amd64       Ta 4K, 2M, 1G
.It armv7       Ta 4K, 1M
.It i386        Ta 4K, 2M (PAE), 4M
.It powerpc     Ta 4K
.It powerpcspe  Ta 4K
.It powerpc64   Ta 4K
.It powerpc64le Ta 4K
.It riscv64     Ta 4K, 2M, 1G
.El
.Ss Floating Point
.Bl -column -offset indent "Architecture" "float, double" "long double"
.It Sy Architecture Ta Sy float, double Ta Sy long double
.It aarch64     Ta hard Ta soft, quad precision
.It amd64       Ta hard Ta hard, 80 bit
.It armv7       Ta hard Ta hard, double precision
.It i386        Ta hard Ta hard, 80 bit
.It powerpc     Ta hard Ta hard, double precision
.It powerpcspe  Ta hard Ta hard, double precision
.It powerpc64   Ta hard Ta hard, double precision
.It powerpc64le Ta hard Ta hard, double precision
.It riscv64     Ta hard Ta hard, quad precision
.El
.Ss Default Tool Chain
.Fx
uses
.Xr clang 1
as the default compiler on all supported CPU architectures,
LLVM's
.Xr ld.lld 1
as the default linker, and
ELF Tool Chain binary utilities such as
.Xr objcopy 1
and
.Xr readelf 1 .
.Ss MACHINE_ARCH vs MACHINE_CPUARCH vs MACHINE
.Dv MACHINE_CPUARCH
should be preferred in Makefiles when the generic
architecture is being tested.
.Dv MACHINE_ARCH
should be preferred when there is something specific to a particular type of
architecture where there is a choice of many, or could be a choice of many.
Use
.Dv MACHINE
when referring to the kernel, interfaces dependent on a specific type of kernel
or similar things like boot sequences.
.Bl -column -offset indent "Dv MACHINE" "Dv MACHINE_CPUARCH" "Dv MACHINE_ARCH"
.It Dv MACHINE Ta Dv MACHINE_CPUARCH Ta Dv MACHINE_ARCH
.It arm64 Ta aarch64 Ta aarch64
.It amd64 Ta amd64 Ta amd64
.It arm Ta arm Ta armv7
.It i386 Ta i386 Ta i386
.It powerpc Ta powerpc Ta powerpc, powerpcspe, powerpc64, powerpc64le
.It riscv Ta riscv Ta riscv64
.El
.Ss Predefined Macros
The compiler provides a number of predefined macros.
Some of these provide architecture-specific details and are explained below.
Other macros, including those required by the language standard, are not
included here.
.Pp
The full set of predefined macros can be obtained with this command:
.Bd -literal -offset indent
cc -x c -dM -E /dev/null
.Ed
.Pp
Common type size and endianness macros:
.Bl -column -offset indent "BYTE_ORDER" "Meaning"
.It Sy Macro Ta Sy Meaning
.It Dv __LP64__ Ta 64-bit (8-byte) long and pointer, 32-bit (4-byte) int
.It Dv __ILP32__ Ta 32-bit (4-byte) int, long and pointer
.It Dv BYTE_ORDER Ta Either Dv BIG_ENDIAN or Dv LITTLE_ENDIAN .
.Dv PDP11_ENDIAN
is not used on
.Fx .
.El
.Pp
Architecture-specific macros:
.Bl -column -offset indent "Architecture" "Predefined macros"
.It Sy Architecture Ta Sy Predefined macros
.It aarch64     Ta Dv __aarch64__
.It amd64       Ta Dv __amd64__ , Dv __x86_64__
.It armv7       Ta Dv __arm__ , Dv __ARM_ARCH >= 7
.It i386        Ta Dv __i386__
.It powerpc     Ta Dv __powerpc__
.It powerpcspe  Ta Dv __powerpc__ , Dv __SPE__
.It powerpc64   Ta Dv __powerpc__ , Dv __powerpc64__
.It powerpc64le Ta Dv __powerpc__ , Dv __powerpc64__
.It riscv64     Ta Dv __riscv , Dv __riscv_xlen == 64
.El
.Pp
Compilers may define additional variants of architecture-specific macros.
The macros above are preferred for use in
.Fx .
.Ss Important Xr make 1 variables
Most of the externally settable variables are defined in the
.Xr build 7
man page.
These variables are not otherwise documented and are used extensively
in the build system.
.Bl -tag -width "MACHINE_CPUARCH"
.It Dv MACHINE
Represents the hardware platform.
This is the same as the native platform's
.Xr uname 1
.Fl m
output.
It defines both the userland / kernel interface, as well as the
bootloader / kernel interface.
It should only be used in these contexts.
Each CPU architecture may have multiple hardware platforms it supports
where
.Dv MACHINE
differs among them.
It is used to collect together all the files from
.Xr config 8
to build the kernel.
It is often the same as
.Dv MACHINE_ARCH
just as one CPU architecture can be implemented by many different
hardware platforms, one hardware platform may support multiple CPU
architecture family members, though with different binaries.
For example,
.Dv MACHINE
of i386 supported the IBM-AT hardware platform while the
.Dv MACHINE
of pc98 supported the Japanese company NEC's PC-9801 and PC-9821
hardware platforms.
Both of these hardware platforms supported only the
.Dv MACHINE_ARCH
of i386 where they shared a common ABI, except for certain kernel /
userland interfaces relating to underlying hardware platform
differences in bus architecture, device enumeration and boot interface.
Generally,
.Dv MACHINE
should only be used in src/sys and src/stand or in system imagers or
installers.
.It Dv MACHINE_ARCH
Represents the CPU processor architecture.
This is the same as the native platforms
.Xr uname 1
.Fl p
output.
It defines the CPU instruction family supported.
It may also encode a variation in the byte ordering of multi-byte
integers (endian).
It may also encode a variation in the size of the integer or pointer.
It may also encode a ISA revision.
It may also encode hard versus soft floating point ABI and usage.
It may also encode a variant ABI when the other factors do not
uniquely define the ABI.
It, along with
.Dv MACHINE ,
defines the ABI used by the system.
Generally, the plain CPU name specifies the most common (or at least
first) variant of the CPU.
This is why powerpc and powerpc64 imply 'big endian' while armv7 and aarch64
imply little endian.
If we ever were to support the so-called x32 ABI (using 32-bit
pointers on the amd64 architecture), it would most likely be encoded
as amd64-x32.
It is unfortunate that amd64 specifies the 64-bit evolution of the x86 platform
(it matches the 'first rule') as almost everybody else uses x86_64.
The
.Fx
port was so early, it predated processor name standardization after Intel joined
the market.
At the time, each OS selected its own conventions.
Backwards compatibility means it is not easy to change to the consensus name.
.It Dv MACHINE_CPUARCH
Represents the source location for a given
.Dv MACHINE_ARCH .
It is generally the common prefix for all the MACHINE_ARCH that
share the same implementation, though 'riscv' breaks this rule.
While amd64 and i386 are closely related, MACHINE_CPUARCH is not x86
for them.
The
.Fx
source base supports amd64 and i386 with two
distinct source bases living in subdirectories named amd64 and i386
(though behind the scenes there's some sharing that fits into this
framework).
.It Dv CPUTYPE
Sets the flavor of
.Dv MACHINE_ARCH
to build.
It is used to optimize the build for a specific CPU / core that the
binaries run on.
Generally, this does not change the ABI, though it can be a fine line
between optimization for specific cases.
.It Dv TARGET
Used to set
.Dv MACHINE
in the top level Makefile for cross building.
Unused outside of that scope.
It is not passed down to the rest of the build.
Makefiles outside of the top level should not use it at all (though
some have their own private copy for hysterical raisons).
.It Dv TARGET_ARCH
Used to set
.Dv MACHINE_ARCH
by the top level Makefile for cross building.
Like
.Dv TARGET ,
it is unused outside of that scope.
.El
.Sh SEE ALSO
.Xr src.conf 5 ,
.Xr build 7 ,
.Xr simd 7
.Sh HISTORY
An
.Nm
manual page appeared in
.Fx 11.1 .