Re: [EXT] Re: [PATCH] target/hppa: correct size bit parity for fmpyadd

["Andreas K. Huettel" <dilfridge@gentoo.org>]

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Am Donnerstag, 16. Oktober 2025, 10:49:56 Mitteleuropäische Sommerzeit schrieb Philippe Mathieu-Daudé:
> On 9/10/25 22:51, Gabriel Brookman wrote:
> > For the fmpyadd instruction on the hppa architecture, there is a bit
> > used to specify whether the instruction is operating on a 32 bit or 64
> > bit floating point register. For most instructions, such a bit is 0 when
> > operating on the smaller register and 1 when operating on the larger
> > register. However, according to page 6-57 of the PA-RISC 1.1 Architecture
> > and Instruction Set Reference Manual, this convention is reversed for the
> > fmpyadd instruction specifically, meaning the bit is 1 for operations on
> > 32 bit registers and 0 for 64 bit registers. Previously, QEMU decoded
> > this operation as operating on the other size of register, leading to
> > bugs when translating the fmpyadd instruction. This patch fixes that
> > issue.
> > 
> > Reported-by: Andreas Hüttel <andreas.huettel@ur.de>
> > Signed-off-by: Gabriel Brookman <brookmangabriel@gmail.com>
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3096
> > ---
> > Hi all,
> > 
> > This patch fixes the decoding of the fmpyadd instruction on the hppa
> > target, which uses an inverted bit convention to select between
> > 32-bit and 64-bit floating-point registers. The issue was reported by
> > Andreas Hüttel after observing incorrect behavior when running real
> > binaries under that target. He kindly submitted a minimal reproducer
> > which I was able to use to debug the issue. I used this reproducer
> > to verify correct operation after my fix.
> > 
> > Thanks,
> > Gabriel
> > 
> > Reported-by: Andreas Hüttel
> > ---
> >   target/hppa/insns.decode | 8 ++++----
> >   1 file changed, 4 insertions(+), 4 deletions(-)
> 
> Patch queued (including doc refs Andreas added).
> 

Thank you all! 

Will eventually help a lot here
https://www.gentoo.org/downloads/#hppa
(which is right now still blocked by an unrelated python bug)


-- 
Andreas K. Hüttel
dilfridge@gentoo.org
Gentoo Linux developer
(council, toolchain, base-system, perl, libreoffice)

-- 
PD Dr. Andreas K. Huettel
Institute for Experimental and Applied Physics
University of Regensburg
93040 Regensburg
Germany

tel. +49 151 241 67748 (mobile)
tel. +49 941 943 1618 (office)
e-mail andreas.huettel@ur.de
https://www.akhuettel.de/
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