Re: Help with -march and -mcpu issues

[Rick Mann <rmann at latencyzero dot com>]

On Aug 29, 2007, at 6:49 PM, Brian Dessent wrote:

> Rick Mann wrote:
>
> > $ arm-elf-gcc -c main.c -o main.o
> > $ arm-elf-ld  -e _start -o h.elf --script=link.lds start.o main.o
> > $ arm-elf-objcopy --output-target=binary --gap-fill=0xff h.elf h
> >
> > The resulting file "h" works very well.
> >
> > However, if I add -mcpu=xscale or -march=armv5te to the gcc line, I
> > get errors like this:
> >
> > arm-elf-ld: ERROR: main.o uses VFP instructions, whereas h.elf  
> > does not
>
> You should ask this on the binutils list.  The linker is not  
> provided by
> nor part of gcc, and your question seems to be about the linker.

You're absolutely right, binutils seems to be more appropriate.

> Where does start.o come from?  Are you not also rebuilding it with the
> given -march?  I'm guessing that the reason you get the error is that
> the linker sees two objects that were built with different -march
> settings (or rather one with the default and another with something
> else), and that's why it's complaining.  But that's just  
> speculation, I
> don't actually know.

Sorry, I meant to sanitize that out. I have a simple file start.S  
which provides a bit of glue and BSS clearing before calling main.  
It's also built with the same -march setting.

The thing that bugs me, again, is that it's complaining about  
differences between the .o files and the thing it's linking the .o  
files into, which is made up only of those .o files!

$ arm-elf-gcc -march=armv5te -ffreestanding -nostdlib -std=c99 - 
Xlinker -e -Xlinker _start -Xlinker --script=link.lds -o h.elf  
start.o main.o -lgcc -lc -lm
/usr/local/arm-4.2.0/lib/gcc/arm-elf/4.2.0/../../../../arm-elf/bin/ 
ld: ERROR: obj/main.o uses VFP instructions, whereas h.elf does not
/usr/local/arm-4.2.0/lib/gcc/arm-elf/4.2.0/../../../../arm-elf/bin/ 
ld: failed to merge target specific data of file obj/main.o


Interestingly, it doesn't seem to complain about start.o.

--
Rick