Re: [Gnewsense-dev] binutils which works around loongson2f NOP bug by default

[Karl Goetz]

On Wed, 7 Apr 2010 13:12:51 -0400
Mark H Weaver <address@hidden> wrote:

> Hello all,
> 
> I would like to propose that gNewSense should include an assembler
> which works around the loongson2f NOP bug by default, without having
> to explicitly pass any additional compiler flags.

That would be nice.

> The workaround does not add any significant overhead, and will work
> just fine on other MIPS-based systems.  There are a great variety of
> build systems out there, including simple Makefiles which would have
> to be edited by hand.  It would be an enormous amount of work to
> create and maintain a delta for each individual source package to
> compile with the new flags.  Anyway, users should be able to use the
> compiler without any special flags to produce executables which do not
> cause hard lockups.

This issue has been discussed on debian-mips, and on this list
previously. Are you aware of those discussions?

> I have prepared new packages based on binutils-2.20-4~bpo50+1 from
> lenny-backports, with the following changes:
> 
> * Backported workarounds for loongson2f bugs from binutils CVS.

IIRC this patch will be available from 2.22 onwards? (A Lemote or
binutils person able to confirm that?)

> * Added --enable-fix-loongson2f-nop option to gas/configure,
>   which makes -mfix-loongson2f-nop the default for MIPS targets
>   (unless overridden by -mnofix-loongson2f-nop).
> 
> * Pass --enable-fix-loongson2f-nop by default from debian/rules.

This enables it by default for all packages built with binutils?

> * Fixed some tests in the testsuites to take into account the new
>   behavior wrt loongson2f workarounds.
> 
> I have attached a patch relative to binutils-2.20-4~bpo50+1.  Note
> that I don't have previous experience modifying Debian source
> packages, so I've probably done some things suboptimally.

I'll have a look, but cant promise to check before the weekend. If
someone else can jump in with a checkover, that would be great.

> I've also built binary packages for mipsel and placed them in
> fencepost.gnu.org:~mhw/binutils-metad/

Fencepost.gnu.org/~mhw/binutils-metad/ offers me a bin, is that
expected?

> These binary packages have been bootstrapped on a Yeeloong with metad,
> using an earlier build of the same binutils packages.
> 
> Ideally, I'd like to submit a patch to the upstream binutils to
> support the --enable-fix-loongson2f-nop configure option, so
> eventually the only delta for gNewSense would be to pass that option
> from debian/rules.

I hope upstream will do this for themselves. Hopefully Lemote/binutils
people can confirm.
kk

> What do you all think of this idea?
> 
>    Thanks,
>      Mark


-- 
Karl Goetz, (Kamping_Kaiser / VK5FOSS)
Debian contributor / gNewSense Maintainer
http://www.kgoetz.id.au
No, I won't join your social networking group

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