l...@gnu.org (Ludovic Courtès) writes: > Mark H Weaver <m...@netris.org> skribis: > >> I chose system name "armhf-linux", GNU triplet "arm-linux-gnueabihf", >> and the following GCC configure flags: >> >> --with-arch=armv7-a >> --with-float=hard >> --with-mode=thumb >> --with-fpu=vfpv3-d16 > > Does it mean that GCC generates Thumb code by default?
Yes. I confess that I'm not sufficiently knowledgeable about ARM to understand the tradeoffs here, and have simply followed Debian's lead. There is some rationale here: https://wiki.debian.org/ArmHardFloatPort There, it says: Thumb-2/ThumbEE: Thumb-2 provides code size improvements and unlike thumb(1) there is no interworking overhead except in a few corner cases. Also Thumb-2 is sufficiently complete that there is no need to fall back to ARM ISA for some operations (unlike thumb1). Thus defaulting to Thumb-2 on v7 or later makes sense. I haven't yet verified that our GCC is generating Thumb-2 instructions (as opposed to Thumb-1). Debian's GCC apparently does, but they apply a rather large patch from Linaro. This should be checked at some point. Anyway, here are some more links that might be worth looking at if we run into build problems: https://wiki.ubuntu.com/ARM/Thumb2 https://wiki.ubuntu.com/ARM/Thumb2PortingHowto Regards, Mark
