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Message-ID: <20251206004018.GF1827@brightrain.aerifal.cx>
Date: Fri, 5 Dec 2025 19:40:18 -0500
From: Rich Felker <dalias@...c.org>
To: Markus Wichmann <nullplan@....net>
Cc: musl@...ts.openwall.com
Subject: Re: How supported is Thumb 1?
On Fri, Dec 05, 2025 at 10:25:54PM +0100, Markus Wichmann wrote:
> Hi all,
>
> I recently got into reading ARM assembly, and then noticed a couple of
> weird things in musl's sources. In particular, at the moment, compiling
> musl with "-march=armv4t -mthumb" produces non-working binaries. Or at
> least I assume so, I haven't actually checked. But the code sequences
> contained in the object files are specifically called out in the AAPCS
> as not working.
Can you test with -march set to whatever the cortex-m model that's
based on armv6 is? I believe there's one that's only "thumb1" (no
32-bit arm isa) but that actually supports everything we use, and this
is what the "thumb1" support was added for. At present there's
probably very little point in supporting it since we don't have fdpic
support on arm, but the intent was to support that. And technically it
does work now as long as you use pie; just it won't be shareable text.
Rich
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