Re: Problems with Newlib built with Clang for Cortex-M

"Keith Packard" <[email protected]> Wed, 31 Oct 2018 07:40:04 -0700

Newsgroups	gmane.comp.lib.newlib
Message-ID	<[email protected]>

"Richard Earnshaw (lists)" <[email protected]> writes:

> These sound like your stack is not correctly aligned: a common symptom
> of failing to do this is that calls to the printf family fail when
> 64-bit sized items (like double) are passed.  The EABI requires 64-bit
> alignment at all function boundaries (and 32-bit alignment at all other
> times).

I ran into this with one embedded platform that wasn't aligning the
initial thread stack on 64-bit boundaries. The compiler was carefully
counting pushes/pops for non-varargs functions, but varargs was
computing the rounding and because the initial stack point was
mis-aligned, everything "worked" except for 64-bit (double) values to
printf which got fetched from the wrong address.

-- 
-keith

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