Re: [poke 2.0] sourcery-arm-thumb2 issue

[Luca Saiu]

Hello.

On 2022-01-29 at 00:26 +0100, Romain Naour wrote:

> I did a test build using poke 2.0:
> https://gitlab.com/kubu93/buildroot/-/pipelines/458944376
>
> There is only one issue with the toolchain sourcery-arm-thumb2 generating 
> thum2
> instruction.

Interesting.

I think Mohammad tried to make me notice a similar thing the other
night, but I am understanding only now.  It is easy to fix, in case you
want to install a small change set yourself; otherwise we can wait for
poke's next bugfix release.

> Error: value of 13865506 too large for field of 2 bytes at 72848
> Error: invalid swi expression

Now, why in the world should I use a software interrupt instruction,
which serves to crash on purpose?  Well, in order to notice when control
reaches a point that is not supposed to reach.  The instruction comes
from the expansion of _JITTER_ASM_CRASH , which on ARM (see
machine/arm/jitter/machine/jitter-machine.h ) is defined as

  "swi 13865506" //"mov r15, #0"

The immediate is too large to fit in Thumb instructions.

Now, why did I choose that ridiculous constant which is equal to 256³
instead of something small?  Probably I wanted to be sure not to
generate a valid kernel call by hazard.

The solution is replacing the 13865506 literal with something small: I
see from the documentation that any 16-bit “swi number” will fit -- I
suppose unsigned.  Let us pick, arbitrarily, 1025.

The fix is on Jitter master:
http://git.ageinghacker.net/jitter/commit/?id=d715f2ea170099d537f28181cf825786a4b019ee

Could you please confirm that this solves the problem?  José and the
other poke friends: this can go into the next bugfix release.

Regards,

-- 
Luca Saiu
* My personal web site:  http://ageinghacker.net
* GNU Jitter:            https://www.gnu.org/software/jitter
* GNU epsilon:           https://www.gnu.org/software/epsilon

I support everyone's freedom of mocking any opinion or belief, no
matter how deeply held, with open disrespect and the same unrelented
enthusiasm of a toddler who has just learned the word "poo".

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