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Manual Pages  — ARCH

NAME

arch – Architecture-specific details

CONTENTS

DESCRIPTION

Differences between CPU architectures and platforms supported by FreeBSD .

Introduction

This document is a quick reference of key ABI details of FreeBSD architecture ports. For full details consult the processor-specific ABI supplement documentation.

If not explicitly mentioned, sizes are in bytes. The architecture details in this document apply to FreeBSD 13.0 and later, unless otherwise noted.

FreeBSD uses a flat address space. Variables of types unsigned long, uintptr_t, and size_t and pointers all have the same representation.

In order to maximize compatibility with future pointer integrity mechanisms, manipulations of pointers as integers should be performed via uintptr_t or intptr_t and no other types. In particular, long and ptrdiff_t should be avoided.

On some architectures, e.g., powerpc and AIM variants of 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.

On each architecture, the main user mode thread's stack starts near the highest user address and grows down.

FreeBSD architecture support varies by release. This table shows currently supported CPU architectures along with the first FreeBSD release to support each architecture.
Architecture Initial Release

aarch64		 11.0

amd64		 5.1

armv6		 10.0

armv7		 12.0

i386		 1.0

powerpc		 6.0

powerpcspe		 12.0

powerpc64		 9.0

powerpc64le		 13.0

riscv64		 12.0

Discontinued architectures are shown in the following table.
Architecture Initial Release Final Release

alpha		 3.2 6.4

arm		 6.0 12.4

armeb		 8.0 11.4

ia64		 5.0 10.4

mips		 8.0 13.x

mipsel		 9.0 13.x

mipselhf		 12.0 13.x

mipshf		 12.0 13.x

mipsn32		 9.0 13.x

mips64		 9.0 13.x

mips64el		 9.0 13.x

mips64elhf		 12.0 13.x

mips64hf		 12.0 13.x

pc98		 2.2 11.4

riscv64sf		 12.0 13.x

sparc64		 5.0 12.4

Type sizes

All FreeBSD architectures use some variant of the ELF (see elf(5)) Application Binary Interface (ABI) for the machine processor. All supported ABIs can be divided into two groups:
ILP32 int, long, void * types machine representations all have 4-byte size.
LP64 int type machine representation uses 4 bytes, while long and void * are 8 bytes.

Some machines support more than one FreeBSD ABI. Typically these are 64-bit machines, where the "native" LP64 execution environment is accompanied by the "legacy" ILP32 environment, which was the historical 32-bit predecessor for 64-bit evolution. Examples are:
LP64 ILP32 counterpart
amd64 i386
powerpc64 powerpc
aarch64 armv6/armv7

aarch64 will support execution of armv6 or armv7 binaries if the CPU implements AArch32 execution state, however older armv4 and armv5 binaries aren't supported.

On all supported architectures:
Type Size

short		 2

int		 4

long		 sizeof(void*)

long long		 8

float		 4

double		 8

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 arm, require only 4-byte alignment for 64-bit integers.

Machine-dependent type sizes:
Architecture void * long double time_t

aarch64		 8 16 8

amd64		 8 16 8

armv6		 4 8 8

armv7		 4 8 8

i386		 4 12 4

powerpc		 4 8 8

powerpcspe		 4 8 8

powerpc64		 8 8 8

powerpc64le		 8 8 8

riscv64		 8 16 8

time_t is 8 bytes on all supported architectures except i386.

Endianness and Char Signedness

Architecture Endianness char Signedness

aarch64		 little unsigned

amd64		 little signed

armv6		 little unsigned

armv7		 little unsigned

i386		 little signed

powerpc		 big unsigned

powerpcspe		 big unsigned

powerpc64		 big unsigned

powerpc64le		 little unsigned

riscv64		 little signed

Page Size

Architecture Page Sizes

aarch64		 4K, 2M, 1G

amd64		 4K, 2M, 1G

armv6		 4K, 1M

armv7		 4K, 1M

i386		 4K, 2M (PAE), 4M

powerpc		 4K

powerpcspe		 4K

powerpc64		 4K

powerpc64le		 4K

riscv64		 4K, 2M, 1G

Floating Point

Architecture float, double long double

aarch64		 hard soft, quad precision

amd64		 hard hard, 80 bit

armv6		 hard hard, double precision

armv7		 hard hard, double precision

i386		 hard hard, 80 bit

powerpc		 hard hard, double precision

powerpcspe		 hard hard, double precision

powerpc64		 hard hard, double precision

powerpc64le		 hard hard, double precision

riscv64		 hard hard, quad precision

Default Tool Chain

FreeBSD uses clang(1) as the default compiler on all supported CPU architectures, LLVM's ld.lld(1) as the default linker, and ELF Tool Chain binary utilities such as objcopy(1) and readelf(1).

MACHINE_ARCH vs MACHINE_CPUARCH vs MACHINE

MACHINE_CPUARCH should be preferred in Makefiles when the generic architecture is being tested. 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 MACHINE when referring to the kernel, interfaces dependent on a specific type of kernel or similar things like boot sequences.
MACHINE MACHINE_CPUARCH MACHINE_ARCH

arm64		 aarch64 aarch64

amd64		 amd64 amd64

arm		 arm armv6, armv7

i386		 i386 i386

powerpc		 powerpc powerpc, powerpcspe, powerpc64, powerpc64le

riscv		 riscv riscv64

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.

The full set of predefined macros can be obtained with this command: 

cc -x c -dM -E /dev/null

Common type size and endianness macros:
Macro Meaning
__LP64__ 64-bit (8-byte) long and pointer, 32-bit (4-byte) int
__ILP32__ 32-bit (4-byte) int, long and pointer
BYTE_ORDER Either BIG_ENDIAN or LITTLE_ENDIAN. PDP11_ENDIAN is not used on FreeBSD .

Architecture-specific macros:
Architecture Predefined macros

aarch64		 __aarch64__

amd64		 __amd64__, __x86_64__

armv6		 __arm__, __ARM_ARCH >= 6

armv7		 __arm__, __ARM_ARCH >= 7

i386		 __i386__

powerpc		 __powerpc__

powerpcspe		 __powerpc__, __SPE__

powerpc64		 __powerpc__, __powerpc64__

powerpc64le		 __powerpc__, __powerpc64__

riscv64		 __riscv, __riscv_xlen == 64

Compilers may define additional variants of architecture-specific macros. The macros above are preferred for use in FreeBSD .

Importantmake(1) variables

Most of the externally settable variables are defined in the build(7) man page. These variables are not otherwise documented and are used extensively in the build system.
MACHINE Represents the hardware platform. This is the same as the native platform's uname(1) -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 MACHINE differs among them. It is used to collect together all the files from config(8) to build the kernel. It is often the same as 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, MACHINE of i386 supported the IBM-AT hardware platform while the MACHINE of pc98 supported the Japanese company NEC's PC-9801 and PC-9821 hardware platforms. Both of these hardware platforms supported only the 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, MACHINE should only be used in src/sys and src/stand or in system imagers or installers.
MACHINE_ARCH Represents the CPU processor architecture. This is the same as the native platforms uname(1) -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 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 'armv6' and 'armv7' 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 everybody else uses x86_64. There is no standard name for the processor: each OS selects its own conventions.
MACHINE_CPUARCH
  Represents the source location for a given 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 FreeBSD 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).
CPUTYPE Sets the flavor of 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.
TARGET Used to set 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).
TARGET_ARCH Used to set MACHINE_ARCH by the top level Makefile for cross building. Like TARGET, it is unused outside of that scope.

SEE ALSO

src.conf(5), build(7), simd(7)

HISTORY

An arch manual page appeared in FreeBSD 11.1 .
ARCH (7) February 4, 2025
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