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Date: Sun, 27 Apr 2014 14:00:32 -0400
From: Rich Felker <>
Subject: Re: Bare metal progress and an oddity.

On Sun, Apr 27, 2014 at 12:37:13PM -0500, Richard Pennington wrote:
> As part of my quixotic quest to run musl on ARM bare metal I've
> started to handle interrupts and an ARM timer to implement the
> clock_* functions to prepare for pre-emptive scheduling of
> pthread_create'd threads. The current sources are here:
> An oddity: If I use printf() to print out values in an interrupt
> handler it sort of works. The format string prints perfectly, but it
> seems that the va_arg values are getting messed up. The stack is
> large enough, fp and sp are sane. Am I missing something in
> pop_arg() that is causing this? Come to think of it, do I have to
> insure a certain stack alignment, for example? Most of the messed up
> values are "long long".
> Any thoughts appreciated.

Yes, ARM EABI requires the stack to be aligned to at least an 8-byte
boundary (maybe 16 but I think 8 is all that's required). If your
stack is only aligned to 4 bytes, this will mess things up badly.


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