libffi on Cortex M4?

libffi on Cortex M4?

[Tor Krill]

Dear list,

I'm trying to crosscompile libffi for a Cortex-M4 platform running
uClinux but this fails miserably during compilation with a:

../src/arm/sysv.S: Assembler messages:
../src/arm/sysv.S:152: Error: selected processor does not support ARM
opcodes
../src/arm/sysv.S:154: Error: attempt to use an ARM instruction on a
Thumb-only processor -- `stmfd sp!,{r0-r3,fp,lr}'
../src/arm/sysv.S:156: Error: attempt to use an ARM instruction on a
Thumb-only processor -- `mov fp,sp'
../src/arm/sysv.S:161: Error: attempt to use an ARM instruction on a
Thumb-only processor -- `sub sp,fp,r2'

My question is simply, is thumb2 on a cortex m4 supported by libffi?
I.e. is it my build setup that is faulty and this should work or is this
unsupported?

sysv.S have indications that it should support thumb instructions but it
seems to be ignored when i compile libffi.

Best!

/Tor

Re: libffi on Cortex M4?

[Richard Henderson]

On 09/14/2015 11:43 AM, Tor Krill wrote:
> Dear list,
> 
> I'm trying to crosscompile libffi for a Cortex-M4 platform running
> uClinux but this fails miserably during compilation with a:
> 
> ../src/arm/sysv.S: Assembler messages:
> ../src/arm/sysv.S:152: Error: selected processor does not support ARM
> opcodes
> ../src/arm/sysv.S:154: Error: attempt to use an ARM instruction on a
> Thumb-only processor -- `stmfd sp!,{r0-r3,fp,lr}'
> ../src/arm/sysv.S:156: Error: attempt to use an ARM instruction on a
> Thumb-only processor -- `mov fp,sp'
> ../src/arm/sysv.S:161: Error: attempt to use an ARM instruction on a
> Thumb-only processor -- `sub sp,fp,r2'
> 
> My question is simply, is thumb2 on a cortex m4 supported by libffi?
> I.e. is it my build setup that is faulty and this should work or is this
> unsupported?

Thumb2 is supported, but I think you'll find that the M4 is thumb1, which isn't.

We normally expect to have the assembly bits for libffi compiled for arm32 and
use interworking to let the C bits be built for thumb1.  In order to support a
thumb1 only core would require significant work.


r~

Re: libffi on Cortex M4?

[Tor Krill]

Hi Richard and others,

Thank you for a prompt and good answer!

On mån, 2015-09-14 at 12:07 -0700, Richard Henderson wrote:
> On 09/14/2015 11:43 AM, Tor Krill wrote:
> > Dear list,
> > 
> > I'm trying to crosscompile libffi for a Cortex-M4 platform running
> > uClinux but this fails miserably during compilation with a:
> > 
> > ../src/arm/sysv.S: Assembler messages:
> > ../src/arm/sysv.S:152: Error: selected processor does not support ARM
> > opcodes
> > ../src/arm/sysv.S:154: Error: attempt to use an ARM instruction on a
> > Thumb-only processor -- `stmfd sp!,{r0-r3,fp,lr}'
----8<----------------------
> > 
> > My question is simply, is thumb2 on a cortex m4 supported by libffi?
> > I.e. is it my build setup that is faulty and this should work or is this
> > unsupported?
> 
> Thumb2 is supported, but I think you'll find that the M4 is thumb1, which isn't.
>
> We normally expect to have the assembly bits for libffi compiled for arm32 and
> use interworking to let the C bits be built for thumb1.  In order to support a
> thumb1 only core would require significant work.

Now i actually get a bit confused. Excuse me for my lack of low level
arm core knowledge. But Arm says that the Cortex M4 should be Thumb2,
albeit Thumb2 only if i understand correctly.

http://www.arm.com/products/processors/cortex-m/cortex-m4-processor.php

Further more, when i read up on the Cortex M4 users manual it seems like
the assembler instructions i get an error on during build is actually
supported by the cpu. I.e. the stmfd.

Could it be that i have a toolchain problem? (I use a somewhat old gcc
from "Sourcery", Sourcery G++ Lite 2010q1-189 4.4.1)

Best!

/Tor