Allow manually setting the AArch32 instruction set

At the moment the AArch32 instruction set isn't specified in the command
line, which means that the compiler is free to choose the one it sees
fit. This decision may change between compiler versions, so it is better
to specify it manually.

The build option AARCH32_INSTRUCTION_SET has been introduced for this
reason. This option can be set to T32 or A32 to pass the correct flags
to the compiler.

The current behaviour is to default to T32 due to it's smaller size.

Change-Id: I02297eb1d9404b5868ff7c054fbff9b3cda7fdb6
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

Makefile

@@ -166,6 +166,14 @@ TF_CFLAGS_aarch64	=	-march=armv8-a
 LD			=	$(LINKER)
 endif
 
+ifeq (${AARCH32_INSTRUCTION_SET},A32)
+TF_CFLAGS_aarch32	+=	-marm
+else ifeq (${AARCH32_INSTRUCTION_SET},T32)
+TF_CFLAGS_aarch32	+=	-mthumb
+else
+$(error Error: Unknown AArch32 instruction set ${AARCH32_INSTRUCTION_SET})
+endif
+
 TF_CFLAGS_aarch32	+=	-mno-unaligned-access
 TF_CFLAGS_aarch64	+=	-mgeneral-regs-only -mstrict-align
 

docs/user-guide.rst

@@ -75,7 +75,7 @@ In addition, the following optional packages and tools may be needed:
 
 -  To create and modify the diagram files included in the documentation, `Dia`_.
    This tool can be found in most Linux distributions. Inkscape is needed to
-   generate the actual *.png files.
+   generate the actual \*.png files.
 
 Getting the TF-A source code
 ----------------------------
@@ -212,6 +212,10 @@ performed.
 Common build options
 ^^^^^^^^^^^^^^^^^^^^
 
+-  ``AARCH32_INSTRUCTION_SET``: Choose the AArch32 instruction set that the
+   compiler should use. Valid values are T32 and A32. It defaults to T32 due to
+   code having a smaller resulting size.
+
 -  ``AARCH32_SP`` : Choose the AArch32 Secure Payload component to be built as
    as the BL32 image when ``ARCH=aarch32``. The value should be the path to the
    directory containing the SP source, relative to the ``bl32/``; the directory

make_helpers/defaults.mk

@@ -10,6 +10,9 @@
 # poised to handle dependencies, as all build variables would have a default
 # value by then.
 
+# Use T32 by default
+AARCH32_INSTRUCTION_SET		:= T32
+
 # The AArch32 Secure Payload to be built as BL32 image
 AARCH32_SP			:= none