From: Guenter Roeck <linux@roeck-us.net>
To: "Maciej W. Rozycki" <macro@imgtec.com>
Cc: Matthew Fortune <Matthew.Fortune@imgtec.com>,
Ralf Baechle <ralf@linux-mips.org>,
"linux-mips@linux-mips.org" <linux-mips@linux-mips.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
James Hogan <James.Hogan@imgtec.com>
Subject: Re: [PATCH] MIPS: VDSO: Always select -msoft-float
Date: Fri, 4 Nov 2016 09:50:47 -0700 [thread overview]
Message-ID: <20161104165047.GA29628@roeck-us.net> (raw)
In-Reply-To: <alpine.DEB.2.00.1611041558460.13938@tp.orcam.me.uk>
On Fri, Nov 04, 2016 at 04:09:37PM +0000, Maciej W. Rozycki wrote:
> On Fri, 4 Nov 2016, Guenter Roeck wrote:
>
> > > As above, unless absolutely critical to have floating point code then
> > > the vDSO should just avoid all FP related issues and build soft-float.
> >
> > FWIW, my logic was quite simple: The rest of the kernel builds with
> > -msoft-float, thus vDSO should do the same. Of course, I don't know the
> > entire context, so there may well be a reason to handle it differently
> > than the rest of the kernel.
>
> VDSO is not a part of the kernel, it's user mode code, made visible in
> the user virtual memory, and implicitly loaded along the rest of the DSOs
> on program startup by the dynamic loader (ld.so). It has to be PIC for
> that reason, too, causing all the hassle we had with making it such that
> it does not need a GOT.
>
> > Anyway, isn't the kernel supposed to not use floating point operations
> > in the first place ? Is this different for vDSO ?
>
> This code is executed in the user mode so while floating-point code may
> not be needed there, not at least right now, there's actually nothing
> which should stop us from from adding some should such a need arise.
>
Just for my understanding - so the code is compiled with the kernel and part
of the kernel source but executed in user mode ?
If you ever add real floating point code, doesn't that also mean that you'll
have to implement the necessary linker helper functions or wrappers (such
as the wrappers needed for 64-bit integer divide operations in 32 bit code) ?
Thanks,
Guenter
next prev parent reply other threads:[~2016-11-04 16:51 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-30 16:05 [PATCH] MIPS: VDSO: Always select -msoft-float Guenter Roeck
2016-11-01 22:40 ` Maciej W. Rozycki
2016-11-01 22:40 ` Maciej W. Rozycki
2016-11-01 23:30 ` Guenter Roeck
2016-11-04 12:54 ` Maciej W. Rozycki
2016-11-04 12:54 ` Maciej W. Rozycki
2016-11-04 13:42 ` Matthew Fortune
2016-11-04 15:26 ` Guenter Roeck
2016-11-04 16:09 ` Maciej W. Rozycki
2016-11-04 16:50 ` Guenter Roeck [this message]
2016-11-04 18:06 ` Maciej W. Rozycki
2016-11-04 16:55 ` Matthew Fortune
2016-11-04 18:33 ` Guenter Roeck
2016-11-04 19:07 ` Maciej W. Rozycki
2016-11-23 0:08 ` Maciej W. Rozycki
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