I'm trying to build the foreign function interface library for a Cortex-M3 processor using GCC. According to http://gcc.gnu.org/onlinedocs/gcc/ARM-Options.html:
-mthumb
Generate code for the Thumb instruction set. The default is to use the 32-bit ARM instruction set. This option automatically enables either 16-bit Thumb-1 or mixed 16/32-bit Thumb-2 instructions based on the -mcpu=name and -march=name options. This option is not passed to the assembler. If you want to force assembler files to be interpreted as Thumb code, either add a `.thumb' directive to the source or pass the -mthumb option directly to the assembler by prefixing it with -Wa.
I've tried passing various various arguments to the assembler and can't seem to figure it out. Typical output as follows:
Building file: ../source/ffi/sysv.S
Invoking: GCC Assembler
arm-bare_newlib_cortex_m3_nommu-eabi-gcc -Wa,-mthumb-interwork -I"/home/neil/m3projects/robovero/firmware/include" -o"source/ffi/sysv.o" "../source/ffi/sysv.S"
../source/ffi/sysv.S: Assembler messages:
../source/ffi/sysv.S:145: Error: selected processor does not support ARM opcodes
../source/ffi/sysv.S:147: Error: attempt to use an ARM instruction on a Thumb-only processor -- `stmfd sp!,{r0-r3,fp,lr}'
...
Can I use libffi on Cortex-M3 without becoming an assembly expert?
It might be worth noting that when I invoke arm-bare_newlib_cortex_m3_nommu-eabi-as directly I get different errors.
I hate to say it but it is a porting effort. Doable, not necessarily having to be an assembler expert, but will need to learn some. Going from thumb to arm is easy, thumb2, I would have to look that up, much of thumb2 is just thumb instructions. and thumb has a one to one mapping to arm instructions, but not the other way around. Thumb mostly limits you to the lower 8 registers on all the workhorse instructions, with special versions or special instructions to use the upper registers. So many of your arm instructions are going to turn into more than one thumb instruction.
Initially see if there is a build option to build this package without using assembler or go into that directory and see if there is something you can do in the makefile to use a C program instead of assembler. I assume there is a serious performance issue to using C which is why there is assembler to start with. Thumb2 in theory is more efficient than arm but that does not necessarily mean a direct port from arm to thumb2. So with some experience you may be able to hand port to thumb2 and keep some performance.
EDIT:
Downloaded the file in question. The define stuff up front implies that it is aware of both thumb and armv7m. is that how you are getting to where you were changing stm to push?