Index: share/man/man7/arch.7
===================================================================
--- share/man/man7/arch.7
+++ share/man/man7/arch.7
@@ -26,7 +26,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd May 3, 2017
+.Dd May 4, 2017
 .Dt ARCH 7
 .Os
 .Sh NAME
@@ -35,9 +35,72 @@
 .Sh DESCRIPTION
 Differences between CPU architectures and platforms supported by
 .Fx .
-.Pp
+.Ss Introduction
 If not explicitly mentioned, sizes are in bytes.
+.Pp
+FreeBSD uses flat address space for program execution, where
+pointers have the same binary representation as
+.Vt long
+variables,
+.Vt uintptr_t
+and
+.Vt size_t
+types are synonyms for
+.Vt unsigned long .
+.Pp
+On some architectures (sparc64), kernel uses separate address space.
+On other architectures, kernel address space is shared with user
+address space, kernel is located at highest addresses.
+.Pp
+On each architecture, stack of the main thread starts near highest
+user address and grows down.
 .Ss Type sizes
+On each architecture, FreeBSD uses some variant of ELF (see
+.Xr elf 5 )
+.Sy Application Binary Interface
+(ABI) for the machine processor.
+All supported ABIs can be divided into two groups:
+.Bl -tag -width "Dv ILP32"
+.It Dv ILP32
+.Vt int ,
+.Vt long ,
+.Vt void *
+types machine representations all have 4-byte size.
+.It Dv LP64
+.Vt int
+type machine representation uses 4 bytes,
+while
+.Vt long
+and
+.Vt void *
+are 8 bytes.
+.El
+Compilers define
+.Dv _LP64
+symbol when compiling for an
+.Dv LP64
+ABI.
+.Pp
+Some machines support more that one FreeBSD ABI,
+typically these are 64-bit machines, where
+.Dq native
+.Dv LP64
+execution environment is accompanied by the
+.Dq legacy
+.Dv ILP32
+environment, which was historical 32-bit predecessor for 64-bit evolution.
+Examples are:
+.Bl -column -offset indent "powerpc64" "and powerpc"
+.It Sy LP64        Ta ILP32 counterparts
+.It Dv amd64       Ta Dv i386
+.It Dv powerpc64   Ta Dv powerpc
+.It Dv mips64*      Ta Dv mips*
+.El
+.Dv arm64
+currently does not support execution of
+.Dv armv6
+binaries.
+.Pp
 On all supported architectures:
 .Bl -column -offset -indent "long long" "Size"
 .It Sy Type Ta Sy Size