NAME
arch
—
Architecture-specific
details
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 11.0 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.x |
armv6 | 10.0 | |
armv7 | 12.0 | |
ia64 | 5.0 | 10.4 |
i386 | 1.0 | |
mips | 8.0 | |
mipsel | 9.0 | |
mipselhf | 12.0 | |
mipshf | 12.0 | |
mipsn32 | 9.0 | |
mips64 | 9.0 | |
mips64el | 9.0 | |
mips64elhf | 12.0 | |
mips64hf | 12.0 | |
pc98 | 2.2 | 11.x |
powerpc | 6.0 | |
powerpcspe | 12.0 | |
powerpc64 | 6.0 | |
powerpc64le | 13.0 | |
riscv64 | 12.0 | |
riscv64sf | 12.0 | |
sparc64 | 5.0 | 12.x |
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 |
mips64* |
mips* |
aarch64 |
armv6/armv7 |
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.
Endianness and Char Signedness
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 |
Page Size
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 |
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 |
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 |
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 |
mips | mips | mips, mipsel, mips64, mips64el, mipshf, mipselhf, mips64elhf, mipsn32 |
powerpc | powerpc | powerpc, powerpcspe, powerpc64, powerpc64le |
riscv | riscv | riscv64, riscv64sf |
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__ |
mips | __mips__ ,
__MIPSEB__ ,
__mips_o32 |
mipsel | __mips__ ,
__mips_o32 |
mipselhf | __mips__ ,
__mips_o32 |
mipshf | __mips__ ,
__MIPSEB__ ,
__mips_o32 |
mipsn32 | __mips__ ,
__MIPSEB__ ,
__mips_n32 |
mips64 | __mips__ ,
__MIPSEB__ ,
__mips_n64 |
mips64el | __mips__ ,
__mips_n64 |
mips64elhf | __mips__ ,
__mips_n64 |
mips64hf | __mips__ ,
__MIPSEB__ ,
__mips_n64 |
powerpc | __powerpc__ |
powerpcspe | __powerpc__ ,
__SPE__ |
powerpc64 | __powerpc__ ,
__powerpc64__ |
powerpc64le | __powerpc__ ,
__powerpc64__ |
riscv64 | __riscv ,
__riscv_xlen == 64 |
riscv64sf | __riscv ,
__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.
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 whereMACHINE
differs among them. It is used to collect together all the files from config(8) to build the kernel. It is often the same asMACHINE_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 theMACHINE
of pc98 supported the Japanese company NEC's PC-9801 and PC-9821 hardware platforms. Both of these hardware platforms supported only theMACHINE_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 (e.g., MIPS' n32 ABI). It, along withMACHINE
, 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. 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. 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). 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. LikeTARGET
, it is unused outside of that scope.
SEE ALSO
HISTORY
An arch
manual page appeared in
FreeBSD 11.1.