emitting .eabi_attribute on ARM

[David Monniaux]

Certain embedded toolchains (for assembling and linking) for ARM assume that if a file contains no eabi attribute for floating-point, then it uses soft float. Furthermore, the linker checks that all modules have the same soft/hard float ABI settings. Since CompCert does not emit this attribute, this prevents linking CompCert's output with libraries compiled for hard float.

Solution: emit

  .eabi_attribute Tag_ABI_VFP_args, 1

for hard float parameters (0 for soft float, 3 to say there are no floating-point parameters anyway in this file so it's compatible with both).

See https://reviews.llvm.org/D49993

gcc does set this attribute (instead of printing Tag_ABI_VFP_args it prints its numeric value, 28)

[Xavier Leroy]

Thanks for the tip. Should be fixed by 1d14f7a .