[Buildroot] libgcc erroneously built as armv5 for arm920t(armv4t)

[Yann E. MORIN <yann.morin.1998@free.fr>]

Thomas, Adam, All,

On 2013-09-26 17:54 +0200, Thomas Petazzoni spake thusly:
> Hello,
> 
> On Thu, 26 Sep 2013 08:34:53 -0700 (PDT), adam hussein\(!\) wrote:
> > I've been building the at91rm9200ek configuration of buildroot to get
> > a toolchain I can use to build u-boot with some board specific
> > configuration.
> > 
> > This is an ARM920T core chip with ARMv4T architecture??- later ARM9
> > series have ARMv5TE architecture (http://en.wikipedia.org/wiki/ARM9)
> > 
> > When gcc is built, or perhaps specifically libgcc only, it seems the
> > selection of 920t/v4 architecture gets lost and v5 is used instead.
> > This means that when I use it to build u-boot, I find it has the
> > __udivsi3 function using the illegal (to v4) instruction CLZ (count
> > leading zeros).
> > 
> > The easiest workaround for me is to specify arm7tdmi and be done with
> > it, but I'd like to try contributing a proper fix if possible.
> > 
> > It turns out that this issue has been around for some time:
> > 
> > e.g. 2006: http://www.mail-archive.com/oe at handhelds.org/msg02024.html
> > e.g. 2007:
> > http://permalink.gmane.org/gmane.comp.lib.uclibc.buildroot/3139 e.g.
> > 2007:
> > http://web.archive.org/web/20070815094037/http://bugs.busybox.net/view.php?id=1406
> > (referred to in previous link)
> > 
> > and then the last link has this patch:
> > http://web.archive.org/web/20070815094037/http://bugs.busybox.net/file_download.php?file_id=1059&type=bug
> > 
> > ...which seems not to have made it into the main repo, and no longer
> > applies correctly; all the locations have changed.
> > 
> > 
> > So, here follows an up-to-date version of it. I hope someone finds it
> > useful and avoids repeating all my 'digging about'.
> > 
> > And many thanks to 'bjdooks' for the original.
> 
> Interesting. First, thanks for the investigation.
> 
> When you select BR2_arm920t as the ARM processor, we are already
> passing --with-arch=armv4t to the gcc configure. So, gcc should already
> avoid the use of CLZ, since ARMv4T does not support it.
> 
> Have you investigated why passing the --with-cpu argument is also
> needed, in addition to --with-arch?

In crosstool-Ng, we have this:
    http://crosstool-ng.org/hg/crosstool-ng/annotate/98b7806295cc/patches/gcc/4.4.5/210-arm-unbreak-armv4t.patch#l1

For gcc, if --with-cpu is not specified, then it defaults to
TARGET_CPU_arm10tdmi which is an armv5 (as far as I understand it).

The patch above downgrades the default CPU to an armv4t. Maybe worth a
try. That, or passing --with-cpu=... as suggested by Adam.

Regards,
Yann E. MORIN.

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