Intro.

A new GCC98r2 platform/build target has been added to Cedar. This
platform is called ARM4T and implements the 'mostly thumb' build
policy. Under this policy user-side code is built in THUMB (ARMv4)
mode by default and kernel side code is built in ARM (ARMv4) mode with
no interworking support. These defaults can be overridden by various
means (see below). When the default is overridden both user and
kernel-side code is built in ARM (ARMv4) mode with interworking
support.

Overriding the default.

The default can be overridden at project (MMP)and compontent (BLD.INF)
level and also interactively via a commandline argument to MAKMAKE.

i) MMP 

A new keyword ALWAYS_BUILD_AS_ARM is introduced to the supported MMP
file syntax. This keyword takes no arguments. It applies only to
platforms that implement the 'mostly thumb' policy. In other words it
is ignored by other platforms (e.g. ARM4). 

ii. BLD.INF

A new qualifier, BUILD_AS_ARM, is introduced for MMP file statements
in the BLD.INF syntax. The syntax for such statements thus becomes:

PRJ_MMPFILES
[<mmp path>\<mmp file>] {<qualifiers>}
{MAKEFILE|NMAKEFILE} [<path>\<makefile>] {build_as_arm}
// <qualifiers> are tidy, ignore, build_as_arm

iii. MAKMAKE

MAKMAKE has been extended to accept the option -ARM. Supplying this
option has the same effect as if ALWAYS_BUILD_AS_ARM is supplied in
the MMP file.

Build/Release Directory Structure.

Build artefacts are placed in either UREL or UDEB beneath ARM4T in
both build and release trees whatever ISA is targeted. The exception
is import libraries. Because ARM4T only supports version 4 of the ARM
architecture different import stubs implementations are required for
each of the possible modes that clients can be compiled in (e.g. ARM
without-interworking vs ARM with-interworking vs THUMB). Therefore
import libraries are placed in the UREL sub-directory of ARM4, ARMI or
THUMB respectively within the release tree.

Static Libraries.  

Static libraries are always built in ARM mode with interworking. A
consequence of this is that the linker (LD) will introduce veneers
into executables built in THUMB mode. The veneers are responsible for
switching mode (as appropriate). However the introduction of a veneer
has a small impact on code size. These two factors (i.e. static libs
being ARM and veneers) mean that an ARM4T THUMB executable will always
be slightly larger than if it had been built using the old THUMB build
target.