[llvm-dev] Cross-compiling for ARM Cortex-M3 on x86

[Son Tuan VU via llvm-dev]

@ Christophe: Oh wow yes adding these option to link command does indeed
solve the problem. Thank you so much!
@ Peter: Yes I've found the samples. I should have look at these sooner.
Thanks for the pointer!

Son Tuan Vu

On Mon, Mar 12, 2018 at 4:42 PM, Christophe Lyon <christophe.lyon at linaro.org
> wrote:

> On 12 March 2018 at 16:35, Son Tuan VU via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > Thanks for your prompt reply.
> >
> > I didn't build the libc at all, I downloaded a pre-built version of the
> > whole toolchain from
> > https://developer.arm.com/open-source/gnu-toolchain/gnu-rm/downloads,
> so I
> > guess it is an official version provided by ARM and should work? This
> > version targets ARM Cortex-M and Cortex-R family of processors...
> >
>
> I believe these GCC toolchains are multilib-enabled (that is, the libs are
> built
> multiple times, with different options, including thumb/arm).
>
> Since you already use the gcc driver to link your program,
> adding -mcpu=cortex-m3 -mthumb to your link line should do the trick.
>
> To see which multilibs are available in your GCC toolchain, use:
> arm-none-eabi-gcc --print-multi-lib
>
> HTH
>
> Christophe
>
>
> > Son Tuan Vu
> >
> > On Mon, Mar 12, 2018 at 4:15 PM, Tim Northover <t.p.northover at gmail.com>
> > wrote:
> >>
> >> Hi,
> >>
> >> On 12 March 2018 at 15:06, Son Tuan VU via llvm-dev
> >> <llvm-dev at lists.llvm.org> wrote:
> >> > But libc code is in ARM mode:
> >>
> >> That's very bad, because Cortex-M doesn't support ARM mode. I think
> >> your libc is broken.
> >>
> >> > As you can see, the call to srand is just a bl (Branch with Link),
> not a
> >> > blx
> >> > (Branch with Link and Exchange instruction set), so I think something
> is
> >> > going wrong here.
> >>
> >> Yes, Cortex-M has no blx instruction.
> >>
> >> > Can anyone kindly give me some pointers on how to debug this? Or at
> >> > least
> >> > tell me whether this is a bug?
> >>
> >> You don't mention how you build libc, but that's what you need to fix.
> >>
> >> > I am a bit lost now, I've tried to look up
> >> > for more information on this but cannot find out why Clang doesn't
> >> > generate
> >> > Thumb code for libc functions.
> >>
> >> It'll be part of your libc's build system (Makefile?). Clang should
> >> simply refuse to produce ARM mode code if it knows it's targeting
> >> Cortex-M, so my guess is no -mcpu option is being specified. There
> >> might be subtle differences in how GCC has been compiled that means
> >> your version defaults to Thumb mode anyway, but Clang doesn't.
> >>
> >> Cheers.
> >>
> >> Tim.
> >
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > llvm-dev at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
> >
>
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