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ARCH(7)		     BSD 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 sup-
     plement documentation.

     If	not explicitly mentioned, sizes	are in bytes.  The architecture	de-
     tails in this document apply to FreeBSD 10.0 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 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., sparc64, powerpc and AIM variants of
     powerpc64,	the kernel uses	a separate address space.  On other architec-
     tures, 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
	   armeb	      8.0		    11.x
	   armv6	      10.0
	   armv7	      12.0
	   ia64		      5.0		    10.x
	   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
	   riscv64	      12.0
	   riscv64sf	      12.0
	   sparc64	      5.0

   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.
     Compilers define the _LP64	symbol when compiling for an LP64 ABI.

     Some machines support more	that one FreeBSD ABI.  Typically these are
     64-bit machines, where the	"native" LP64 execution	environment is accom-
     panied by the "legacy" ILP32 environment, which was historical 32-bit
     predecessor for 64-bit evolution.	Examples are:

	   LP64		   ILP32 counterpart
	   amd64	   i386
	   powerpc64	   powerpc
	   mips64*	   mips*
     aarch64 currently does not	support	execution of armv6 or armv7 binaries,
     even if the CPU implements	AArch32	execution state.

     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, re-
     quire 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
	   arm		      4		   8		     8
	   armv6	      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
	   riscv64	      8		   16		     8
	   riscv64sf	      8		   16		     8
	   sparc64	      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
	   arm		      little	       unsigned
	   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
	   riscv64	      little	       signed
	   riscv64sf	      little	       signed
	   sparc64	      big	       signed

   Page	Size
	   Architecture	      Page Sizes
	   aarch64	      4K, 2M, 1G
	   amd64	      4K, 2M, 1G
	   arm		      4K
	   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
	   riscv64	      4K
	   riscv64sf	      4K
	   sparc64	      8K

   Floating Point
	   Architecture	      float, double	  long double
	   aarch64	      hard		  soft,	quad precision
	   amd64	      hard		  hard,	80 bit
	   arm		      soft		  soft,	double precision
	   armv6	      hard(1)		  hard,	double precision
	   armv7	      hard(1)		  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
	   riscv64	      hard		  hard,	double precision
	   riscv64sf	      soft		  soft,	double precision
	   sparc64	      hard		  hard,	quad precision

     (1) Prior to FreeBSD 11.0,	armv6 used the softfp ABI even though it sup-
     ported only processors with a floating point unit.

   Predefined Macros
     The compiler provides a number of predefined macros.  Some	of these pro-
     vide 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__
	   arm		      __arm__
	   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__
	   riscv64	      __riscv, __riscv_xlen == 64
	   riscv64sf	      __riscv, __riscv_xlen == 64
	   sparc64	      __sparc64__

     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 exten-
     sively in the build system.

	   MACHINE	  Represent the	hardware platform. This	is the same as
						  the native platform's
						  uname(1) -m output.  It de-
						  fines	both the userland /
						  kernel interface, as well as
						  the bootloader / kernel in-
						  terface.  It should only be
						  used in these	contexts.
						  Each CPU architecture	may
						  have multiple	hardware plat-
						  forms	it supports where
						  MACHINE differs among	them.
						  It is	used to	collect	to-
						  gether all the files from
						  config(8) to build the ker-
						  nel.	It is often the	same
						  as MACHINE_ARCH just as one
						  CPU architecture can be im-
						  plemented by many different
						  hardware platforms, one
						  hardware platform may	sup-
						  port multiple	CPU architec-
						  ture family members, though
						  with different binaries.
						  For example, MACHINE of i386
						  supported the	IBM-AT hard-
						  ware 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 cer-
						  tain kernel /	userland in-
						  terfaces relating to under-
						  lying	hardware platform dif-
						  ferences in bus architec-
						  ture,	device enumeration and
						  boot interface.  Generally,
						  MACHINE should only be used
						  in src/sys and src/stand or
						  in system imagers or in-
						  stallers.
	   MACHINE_ARCH	  Represents the CPU processor architecture. This is
						  the same as the native plat-
						  forms	uname(1) -p output.
						  It defines the CPU instruc-
						  tion family supported.  It
						  may also encode a variation
						  in the byte ordering of
						  multi-byte integers (en-
						  dian).  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 ver-
						  sus soft floating point ABI
						  and usage.  It may also en-
						  code 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 en-
						  coding 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 com-
						  mon (or at least first)
						  variant of the CPU.  This is
						  why mips and mips64 imply
						  'big endian' while 'arm' 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 unfortu-
						  nate 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.	 For example,
						  MACHINE_CPUARCH is defined
						  to be	mips for all the fla-
						  vors 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 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
						  optimization for specific
						  cases.
	   TARGET	  Used to set MACHINE in the top level Makefile	for
						  cross	building.  Unused out-
						  side 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)

HISTORY
     An	arch manual page appeared in FreeBSD 12.

BSD				August 5, 2018				   BSD

NAME | DESCRIPTION | SEE ALSO | HISTORY

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