Add ARM Cortex-M support

[SWW13]

Add ARM Cortex-M support

Description/Motivation/Screenshots

Add a ARM-M architecture as outlined in #571.

I used ARM-M instead of mARM as the later was turned into uppercase which makes it hard to see the relation to ARM.
There is probably a way to auto detect the arch and don't relay on python set_arch('ARM-M'), but I'm not into the gef code base.

This is more or less my workaround and in the "works for me"-state. I'm happy to help test further improvements, but I don't want to spend to much time polishing this.

How Has This Been Tested?

Architecture	Yes/No	Comments
x86-32	✖️
x86-64	✖️
ARM	✖️
AARCH64	✖️
MIPS	✖️
POWERPC	✖️
SPARC	✖️
RISC-V	✖️
make tests	✖️

Checklist

• My PR was done against the dev branch, not master.
• My code follows the code style of this project.
• My change includes a change to the documentation, if required.
• My change adds tests as appropriate.
• I have read and agree to the CONTRIBUTING document.

[jerome-pouiller]

With the fixes suggested in my comments and after run python set_arch('ARM-M'), this patch works.

[Grazfather]

This might be where the name of the register is defined for the BMP implementation of the gdbserver: https://github.com/blacksphere/blackmagic/blob/87acd99fe4c3b75df1423279c6902d1709202a06/src/target/cortexm.c#L151

[Grazfather]

This looks good. "Good enough", though I wish we could more elegantly handle both detection and the _PSR register.

We should probably document this somewhere.

@hugsy do you think we should just mention this pi set_arch(...) in the read me, or add a section to the generated docs?

[hugsy]

@hugsy do you think we should just mention this pi set_arch(...) in the read me, or add a section to the generated docs?

That's a good idea. Maybe expose it in the API documentation ("Extending GEF").

[ikcalB]

When trying this branch, somehowthe context display got messed up?

The following settings are needed, so a context is even displayed:

.gef.rc

[context]
clear_screen = False

[gef]
debug = True

Also the colors are gone, when using tmux-setup

[hugsy]

Due to the recent changes from #779, this new arch can be integrated as part of gef-extras. @SWW13 can you move this PR there instead (in gef-extras/archs) ? It should work out of the box with just the ARM_M class prefixed with the decorator

@register_architecture
class ARM_M(ARM):
    aliases = ("ARM-M",)
    [... rest of the class...]

Cheers

[hugsy]

Closing since hugsy/gef-extras#45 is merged