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ARCH(7) FreeBSD Miscellaneous Information Manual ARCH(7)

Architecture-specific details

Differences between CPU architectures and platforms supported by FreeBSD.

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 12.0 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 the first FreeBSD release to support each architecture, and, for discontinued architectures, the final release.

Architecture Initial Release Final Release
aarch64 11.0
alpha 3.2 6.4
amd64 5.1
arm 6.0 12.x
armeb 8.0 11.4
armv6 10.0
armv7 12.0
ia64 5.0 10.4
i386 1.0
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
powerpc 6.0
powerpcspe 12.0
powerpc64 6.0
powerpc64le 13.0
riscv64 12.0
riscv64sf 12.0
sparc64 5.0 12.x

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:
int, long, void * types machine representations all have 4-byte size.
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

aarch64 will support execution of armv6 or armv7 binaries if the CPU implements AArch32 execution state, however 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
mips 4 8 8
mipsel 4 8 8
mipselhf 4 8 8
mipshf 4 8 8
mipsn32 4 8 8
mips64 8 8 8
mips64el 8 8 8
mips64elhf 8 8 8
mips64hf 8 8 8
powerpc 4 8 8
powerpcspe 4 8 8
powerpc64 8 8 8
powerpc64le 8 8 8
riscv64 8 16 8
riscv64sf 8 16 8

time_t is 8 bytes on all supported architectures except i386.

Architecture Endianness char Signedness
aarch64 little unsigned
amd64 little signed
armv6 little unsigned
armv7 little unsigned
i386 little signed
mips big signed
mipsel little signed
mipselhf little signed
mipshf big signed
mipsn32 big signed
mips64 big signed
mips64el little signed
mips64elhf little signed
mips64hf big signed
powerpc big unsigned
powerpcspe big unsigned
powerpc64 big unsigned
powerpc64le little unsigned
riscv64 little signed
riscv64sf little signed

Architecture Page Sizes
aarch64 4K, 2M, 1G
amd64 4K, 2M, 1G
armv6 4K, 1M
armv7 4K, 1M
i386 4K, 2M (PAE), 4M
mips 4K
mipsel 4K
mipselhf 4K
mipshf 4K
mipsn32 4K
mips64 4K
mips64el 4K
mips64elhf 4K
mips64hf 4K
powerpc 4K
powerpcspe 4K
powerpc64 4K
powerpc64le 4K
riscv64 4K, 2M, 1G
riscv64sf 4K, 2M, 1G

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
mips soft identical to double
mipsel soft identical to double
mipselhf hard identical to double
mipshf hard identical to double
mipsn32 soft identical to double
mips64 soft identical to double
mips64el soft identical to double
mips64elhf hard identical to double
mips64hf hard identical to double
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
riscv64sf soft soft, quad precision

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_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.
arm64 aarch64 aarch64
amd64 amd64 amd64
arm arm armv6, armv7
i386 i386 i386
mips mips mips, mipsel, mips64, mips64el, mipshf, mipselhf, mips64elhf, mipsn32
powerpc powerpc powerpc, powerpcspe, powerpc64, powerpc64le
riscv riscv riscv64, riscv64sf

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
64-bit (8-byte) long and pointer, 32-bit (4-byte) int
32-bit (4-byte) int, long and pointer
Either BIG_ENDIAN or LITTLE_ENDIAN. PDP11_ENDIAN is not used on FreeBSD.

Architecture-specific macros:

Architecture Predefined macros
amd64 , __x86_64__
armv6 , __ARM_ARCH >= 6
armv7 , __ARM_ARCH >= 7
mips , __MIPSEB__, __mips_o32
mipsel , __mips_o32
mipselhf , __mips_o32
mipshf , __MIPSEB__, __mips_o32
mipsn32 , __MIPSEB__, __mips_n32
mips64 , __MIPSEB__, __mips_n64
mips64el , __mips_n64
mips64elhf , __mips_n64
mips64hf , __MIPSEB__, __mips_n64
powerpcspe , __SPE__
powerpc64 , __powerpc64__
powerpc64le , __powerpc64__
riscv64 , __riscv_xlen == 64
riscv64sf , __riscv_xlen == 64, __riscv_float_abi_soft

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

Important make(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.
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.
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 (e.g., MIPS' n32 ABI). It, along with MACHINE, defines the ABI used by the system. For example, the MIPS CPU processor family supports 9 different combinations encoding pointer size, endian and hard versus soft float (for 8 combinations) as well as N32 (which only ever had one variation of all these). Generally, the plain CPU name specifies the most common (or at least first) variant of the CPU. This is why mips and mips64 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.
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. For example, MACHINE_CPUARCH is defined to be mips for all the flavors of mips that we support since we support them all with a shared set of sources. 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).
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.
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).
Used to set MACHINE_ARCH by the top level Makefile for cross building. Like TARGET, it is unused outside of that scope.

src.conf(5), build(7)

An arch manual page appeared in FreeBSD 11.1.
November 25, 2021 FreeBSD 13.1-RELEASE

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