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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 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 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. sparc64, 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.

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 that one FreeBSD ABI. Typically these are 64-bit machines, where the “native” LP64 execution environment is accompanied by the “legacy” ILP32 environment, which was historical 32-bit predecessor for 64-bit evolution. Examples are:

On all supported architectures:

Machine-dependent type sizes:

time_t is 8 bytes on all supported architectures except i386 and 32-bit variants of powerpc.

Endianness and Char Signedness

Page Size

Floating Point

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

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:

Architecture-specific macros: