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D.gnu - versions for thumb and thumb-2 instruction sets

reply Dan Olson <gorox comcast.net> writes:
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?
-- 
Dan
Feb 06 2016
next sibling parent Johannes Pfau <nospam example.com> writes:
Am Sat, 06 Feb 2016 13:58:17 -0800
schrieb Dan Olson <gorox comcast.net>:


 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?


Sorry, I never really used Thumb code so I don't know whether
Thumb1 or Thumb2 would be more useful. But both would be trivial to
implement in GDC, so just choose what you think makes most sense.

Or we could add both ARM_Thumb1 and ARM_Thumb2 versions. If there'll
ever be a Thumb3 we need both anyway.
Feb 07 2016
prev sibling next sibling parent reply Mike <none none.com> writes:
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?


I think to do this properly with ARM you need to consider the ARM 
architecture (ARMv6, ARMv7, ARMv7-A, ARMv7-M, etc..) AND the 
instruction set (ARM or ARM_Thumb).  I read it somewhere, but I'm 
having trouble finding it again.

Anyway, used in conjunction with the architecture, I believe only 
one ARM_Thumb identifier is needed.

It also appears that, with the introduction of AArch64, ARM is 
trying to transition this nomenclature to A32 (ARM), T32 (Thumb), 
A64 (64-bit ARM?).  See 
http://www.arm.com/products/processors/instruction-set-architectures/

Mike

Mike
Feb 07 2016
parent reply Dan Olson <gorox comcast.net> writes:
Mike <none none.com> writes:

 I think to do this properly with ARM you need to consider the ARM
 architecture (ARMv6, ARMv7, ARMv7-A, ARMv7-M, etc..) AND the
 instruction set (ARM or ARM_Thumb).  I read it somewhere, but I'm
 having trouble finding it again.

 Anyway, used in conjunction with the architecture, I believe only one
 ARM_Thumb identifier is needed.

 It also appears that, with the introduction of AArch64, ARM is trying
 to transition this nomenclature to A32 (ARM), T32 (Thumb), A64 (64-bit
 ARM?).  See
 http://www.arm.com/products/processors/instruction-set-architectures/

 Mike


You are right.  I noticed that even thumb-1 has different instruction
set based on arm architecture.  Now that I think about it and
considering Timo's comment that we won't find many thumb-1 devices, it
probably doesn't make sense polluting D with versions that no one will
use (except me).  Probably best approach for me is to just define
ARM_Thumb1 on the command line for my current project.
-- 
Dan
Feb 10 2016
parent reply Mike <none none.com> writes:
On Wednesday, 10 February 2016 at 17:03:35 UTC, Dan Olson wrote:

 I noticed that even thumb-1 has different instruction set based 
 on arm architecture.


Yes.  I did a little more research into this, as it peeked my 
curiosity.  Take a look at this Wikipedia entry 
(https://en.wikipedia.org/wiki/ARM_Cortex-M#Instruction_sets).  I 
haven't verified this information independently, but there you 
can see that although the M0 and M1 support Thumb-1, they don't 
support all of it.  And worse still, they additionally support 
some of Thumb-2.  So "Thumb", "Thumb-1", and "Thumb-2" without 
the architecture/profile are all ambiguous.  As far as I can tell 
the only true indication of the supported instruction set is the 
architecture (ARMv6, ARMv7, ARMv8, etc...), the profile (A, R, 
and M) etc..  AND the target instruction set (ARM "A32", Thumb 
"T32", or A64) -- all three of them together.


 Probably best approach for me is to just define ARM_Thumb1 on 
 the command line for my current project.


If you make versions for the architecture/profile (ARMv6, 
ARMv7-A, ARMv7-M, ARMv7E-M, etc...) I think you only need to 
disambiguate the cases where an architecture/profile supports 
both Thumb and ARM -- like the A profile, if I remember correctly.

So, I still only see the need for one ARM_Thumb instruction set 
identifier, but that could very well be a limitation of my own 
understanding, and a lack of knowledge about your current project.

Mike
Feb 10 2016
parent Dan Olson <gorox comcast.net> writes:
Mike <none none.com> writes:


 On Wednesday, 10 February 2016 at 17:03:35 UTC, Dan Olson wrote:

 I noticed that even thumb-1 has different instruction set based on
 arm architecture.


 Yes.  I did a little more research into this, as it peeked my
 curiosity.


Good info Mike.  Thanks.


 So, I still only see the need for one ARM_Thumb instruction set
 identifier, but that could very well be a limitation of my own
 understanding, and a lack of knowledge about your current project.

 Mike


My current project is a not-so-very-important side project to add
thumb-1 support to druntime for LDC.  It may not really be needed but
thought I'd take a look at it.  I am in the middle of helping cleanup
LDC ARM linux target and have been testing on an original Raspberry Pi
armv6.  I noticed it had thumb-1 and added the extra support to
core.thread.  Now am deciding if it should go anywhere.

For reference, it is this code that started this topic.

https://github.com/smolt/druntime/blob/pi/src/core/thread.d#L2482
Feb 11 2016
prev sibling parent reply Timo Sintonen <t.sintonen luukku.com> writes:
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.
Feb 07 2016
parent Dan Olson <gorox comcast.net> writes:
Timo Sintonen <t.sintonen luukku.com> writes:

 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.


It just made my code uglier with version ARM_Thumb2 only because you
can't do !version like ifndef or !defined.  This is on an armv6 with
thumb1.  I know Walter is not for extra versions if they can be derived
from others though.

version (ARM)
{
    version (ARM_Thumb) // could be thumb1 or thumb2
    {
        version (ARM_Thumb2) {} else version = ARM_Thumb1;
    }

    version (ARM_Thumb1)
    {
        // orginal thumb inline asm
    }
    else
    {
        // arm and thumb-2 inline unified asm
    }
}
Feb 07 2016