On Saturday, 6 February 2016 at 21:58:17 UTC, Dan Olson wrote:
Hi Iain, Johannes. I'm asking here because I don't expect
anybody else is playing with thumb instructions.
Both GDC and LDC have version ARM_Thumb defined for original
thumb (call it thumb-1) and thumb-2. But there is no way to
tell in D code which set is supported.
GCC and clang define these:
__arm__
Always defined when building for the ARM architecture
(regardless of
target instruction set)
__thumb__
Defined only when targeting any Thumb instruction set variant
(Thumb-1
or Thumb-2)
__thumb2__
Defined only when targeting Thumb-2
We could mimic this by adding ARM_Thumb2.
But in my experience it is usually thumb-1 that needs special
handling because it is very limited, and thumb-2 uses unified
assembler so often same code works for either thumb-2 or arm
modes.
So I am thinking that ARM_Thumb1 would be more practical. What
do you think?
Thumb2 is an extension to thumb. It has everything that thumb has
and more. There is nothing in thumb that is not in thumb2. There
is no thumb1. Thumb is sometimes called thumb1 because thumb is
often understood to be both thumb and thumb2.
Thumb2 was introduced to some armv6 devices and it is in all v7
and later devices, including all Cortex ones. I do not remember
dates but I think it has been nearly 10 years that all new
designs have been thumb2. There may not be many old thumb
processors out there any more.
I do not know if there is need to support old thumb any more.
However, if it is wanted, plain thumb or thumb1 is just what is
not thumb2 and can be handled in else branch of thumb2 test.
