1 Intro.

     2 

     3 A new GCC98r2 platform/build target has been added to Cedar. This

     4 platform is called ARM4T and implements the 'mostly thumb' build

     5 policy. Under this policy user-side code is built in THUMB (ARMv4)

     6 mode by default and kernel side code is built in ARM (ARMv4) mode with

     7 no interworking support. These defaults can be overridden by various

     8 means (see below). When the default is overridden both user and

     9 kernel-side code is built in ARM (ARMv4) mode with interworking

    10 support.

    11 

    12 Overriding the default.

    13 

    14 The default can be overridden at project (MMP)and compontent (BLD.INF)

    15 level and also interactively via a commandline argument to MAKMAKE.

    16 

    17 i) MMP 

    18 

    19 A new keyword ALWAYS_BUILD_AS_ARM is introduced to the supported MMP

    20 file syntax. This keyword takes no arguments. It applies only to

    21 platforms that implement the 'mostly thumb' policy. In other words it

    22 is ignored by other platforms (e.g. ARM4). 

    23 

    24 ii. BLD.INF

    25 

    26 A new qualifier, BUILD_AS_ARM, is introduced for MMP file statements

    27 in the BLD.INF syntax. The syntax for such statements thus becomes:

    28 

    29 PRJ_MMPFILES

    30 [<mmp path>\<mmp file>] {<qualifiers>}

    31 {MAKEFILE|NMAKEFILE} [<path>\<makefile>] {build_as_arm}

    32 // <qualifiers> are tidy, ignore, build_as_arm

    33 

    34 iii. MAKMAKE

    35 

    36 MAKMAKE has been extended to accept the option -ARM. Supplying this

    37 option has the same effect as if ALWAYS_BUILD_AS_ARM is supplied in

    38 the MMP file.

    39 

    40 Build/Release Directory Structure.

    41 

    42 Build artefacts are placed in either UREL or UDEB beneath ARM4T in

    43 both build and release trees whatever ISA is targeted. The exception

    44 is import libraries. Because ARM4T only supports version 4 of the ARM

    45 architecture different import stubs implementations are required for

    46 each of the possible modes that clients can be compiled in (e.g. ARM

    47 without-interworking vs ARM with-interworking vs THUMB). Therefore

    48 import libraries are placed in the UREL sub-directory of ARM4, ARMI or

    49 THUMB respectively within the release tree.

    50 

    51 Static Libraries.  

    52 

    53 Static libraries are always built in ARM mode with interworking. A

    54 consequence of this is that the linker (LD) will introduce veneers

    55 into executables built in THUMB mode. The veneers are responsible for

    56 switching mode (as appropriate). However the introduction of a veneer

    57 has a small impact on code size. These two factors (i.e. static libs

    58 being ARM and veneers) mean that an ARM4T THUMB executable will always

    59 be slightly larger than if it had been built using the old THUMB build

    60 target.

    61