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ARCH(7) Miscellaneous Information Manual ARCH(7) 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 archi- tecture ports. For full details consult the processor-specific ABI supplement documentation. If not explicitly mentioned, sizes are in bytes. The architecture de- tails in this document apply to FreeBSD 13.0 and later, unless other- wise 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 mecha- nisms, 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., 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 cur- rently supported CPU architectures along with the first FreeBSD release to support each architecture. Architecture Initial Release aarch64 11.0 amd64 5.1 armv7 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 armv6 10.0 14.x ia64 5.0 10.4 i386 1.0 14.x mips 8.0 13.5 mipsel 9.0 13.5 mipselhf 12.0 13.5 mipshf 12.0 13.5 mipsn32 9.0 13.5 mips64 9.0 13.5 mips64el 9.0 13.5 mips64elhf 12.0 13.5 mips64hf 12.0 13.5 pc98 2.2 11.4 powerpc 6.0 14.x powerpcspe 12.0 14.x riscv64sf 12.0 13.5 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 sup- ported 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 ac- companied 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 armv7 aarch64 will support execution of armv7 binaries if the CPU implements AArch32 execution state. Binaries targeting armv6 and earlier are no longer supported by FreeBSD. 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 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 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, 64K, 2M, 1G amd64 4K, 2M, 1G armv7 4K, 1M i386 4K, 2M (PAE), 4M powerpc 4K powerpcspe 4K powerpc64 4K powerpc64le 4K riscv64 4K, 2M, 1G User Address Space Layout Architecture Maximum Address Address Space Size aarch64 0x0001000000000000 256TiB amd64 (LA48) 0x0000800000000000 128TiB amd64 (LA57) 0x0100000000000000 64PiB armv7 0xbfc00000 3GiB i386 0xffc00000 4GiB powerpc 0xfffff000 4GiB powerpcspe 0x7ffff000 2GiB powerpc64 0x000fffffc0000000 4PiB powerpc64le 0x000fffffc0000000 4PiB riscv64 (Sv39) 0x0000004000000000 256GiB riscv64 (Sv48) 0x0000800000000000 128TiB The layout of a process' address space can be queried via the KERN_PROC_VM_LAYOUT sysctl(3) MIB. Historically, amd64 CPUs were limited to a 48-bit virtual address space. Newer CPUs support 5-level page tables, which extend the sig- nificant bits of addresses to 57 bits (LA57 mode). The address space layout is determined by the CPU's support for LA57. Setting the vm.pmap.la57 tunable to 0 forces the system into 4-level paging mode, even on hardware that supports 5-level paging. In this mode, all processes get a 48-bit address space. The vm.pmap.prefer_la48_uva tun- able determines whether processes running on a LA57 system are limited to a 48-bit address space by default. Some applications make use of unused upper bits in pointer values to store information, and thus im- plicitly assume they are running in LA48 mode. To avoid breaking com- patibility, all processes run in LA48 mode by default. The elfctl(1) utility can be used to request LA48 or LA57 mode for specific executa- bles. Similarly, proccontrol(1) can be used to configure the address space layout when executing a process. The RISC-V specification permits 3-level (Sv39), 4-level (Sv48), and 5-level (Sv57) page tables. Hardware is only required to implement Sv39; implementations which support Sv48 must also support Sv39, and implementations which support Sv57 must also support Sv48. The vm.pmap.mode tunable can be used to select the layout. FreeBSD cur- rently supports Sv39 and Sv48 and defaults to using Sv39. Floating Point Architecture float, double long double aarch64 hard soft, quad precision amd64 hard hard, 80 bit 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 ar- chitectures, LLVM's ld.lld(1) as the default linker, and LLVM 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 ar- chitecture 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 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 in- cluded 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__ 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. 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 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 ar- chitecture can be implemented by many different hard- ware platforms, one hardware platform may support mul- tiple CPU architecture family members, though with different binaries. For example, MACHINE of i386 sup- ported 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 hard- ware 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, de- vice 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 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 FreeBSD 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. 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 implementa- tion, 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 sub- directories named amd64 and i386 (though behind the scenes there's some sharing that fits into this frame- work). 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 opti- mization 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 histori- cal reasons). 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 elfctl(1), proccontrol(1), sysctl(3), src.conf(5), build(7), simd(7) HISTORY An arch manual page appeared in FreeBSD 11.1. FreeBSD 15.0 July 14, 2025 ARCH(7)
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