ancient ARM cpus

[Martin Husemann]

On Sun, Nov 15, 2015 at 08:01:01AM +0100, Niels Möller wrote:
> Where and how do you set ARM_THUMB_MODE? If I understand these things
> correctly, the right check is not whether or not gmp is compiled in
> thumb mode, but whether or not it's going to run on a machine where
> thumb code might call it. Which I guess needs a configure option, since
> it is difficult for configure to guess correctly and automatically.

Oops, indeed, that was not in the patches (and I am not sure we handle
it correctly internally, will have to investigate.)

> What's the corresponding gcc flag to avoid using bx in compiler
> generated code?

If we can get at the gcc defines easily for the m4 stuff, it probably would
be better to use

__ARM_ARCH_ISA_THUMB

which seems to be present if the target cpu supports thumb mode.

You can see it with most arm compilers by doing something like:

arm--netbsdelf-eabi-gcc -mcpu=strongarm110 -dM -E - < /dev/null | fgrep THUMB

which ends up empty, and w/o the -mcpu=strongarm110 you get

#define __ARM_ARCH_ISA_THUMB 1


Martin