RE: [PATCH v2 19/28] arm64/sve: ptrace and ELF coredump support

["Okamoto, Takayuki" <tokamoto at jp dot fujitsu dot com>]

Hi Dave,

Thank you for your reply.

> Your fix looks correct and seems to work.  For stylistic reasons, I may
> write it like this instead, but the effect should be the same:
> 
> 	header->max_vl = sve_max_vl;
> 	if (WARN_ON(!sve_vl_valid(sve_max_vl))
> 		header->max_vl = header->vl;

It is better than my fix.
Please, apply it at next version.

Best regards,
Takayuki Okamoto

> -----Original Message-----
> From: linux-arm-kernel
> [mailto:linux-arm-kernel-bounces@lists.infradead.org] On Behalf Of Dave
> Martin
> Sent: Thursday, September 7, 2017 3:17 AM
> To: Okamoto, Takayuki <tokamoto@jp.fujitsu.com>
> Cc: linux-arch@vger.kernel.org; libc-alpha@sourceware.org; Ard
> Biesheuvel <ard.biesheuvel@linaro.org>; Szabolcs Nagy
> <szabolcs.nagy@arm.com>; gdb@sourceware.org; Yao Qi <Yao.Qi@arm.com>;
> Alan Hayward <alan.hayward@arm.com>; Will Deacon <will.deacon@arm.com>;
> Oleg Nesterov <oleg@redhat.com>; Richard Sandiford
> <richard.sandiford@arm.com>; Alexander Viro <viro@zeniv.linux.org.uk>;
> Catalin Marinas <catalin.marinas@arm.com>; Alex Bennée
> <alex.bennee@linaro.org>; kvmarm@lists.cs.columbia.edu;
> linux-arm-kernel@lists.infradead.org
> Subject: Re: [PATCH v2 19/28] arm64/sve: ptrace and ELF coredump support
> 
> On Wed, Sep 06, 2017 at 04:21:50PM +0000, Okamoto, Takayuki wrote:
> > Hi Dave,
> >
> > I am an engineer of the postK computer from Fujitsu.
> >
> > When I tried to read "max_vl" by ptrace with this patch on our local SVE
> > simulator, it was read as zero.
> > I think the cause of this incident is that "max_vl" is set as "header->vl"
> > only on warning case in sve_init_header_from_task().
> > "max_vl" should be set up also on normal case, like the following patch.
> >
> >
> > --- a/arch/arm64/kernel/ptrace.c
> > +++ b/arch/arm64/kernel/ptrace.c
> > @@ -755,6 +755,8 @@ static void sve_init_header_from_task(struct
> user_sve_header *header,
> >
> >         if (WARN_ON(!sve_vl_valid(sve_max_vl)))
> >                 header->max_vl = header->vl;
> > +       else
> > +               header->max_vl = sve_max_vl;
> >
> >         header->size = SVE_PT_SIZE(vq, header->flags);
> >         header->max_size =
> SVE_PT_SIZE(sve_vq_from_vl(header->max_vl),
> 
> Hi, thanks for reporting this.
> 
> It looks like a refactoring mistake I made while removing BUG_ON()s,
> which I missed in my testing.
> 
> Your fix looks correct and seems to work.  For stylistic reasons, I may
> write it like this instead, but the effect should be the same:
> 
> 	header->max_vl = sve_max_vl;
> 	if (WARN_ON(!sve_vl_valid(sve_max_vl))
> 		header->max_vl = header->vl;
> 
> Cheers
> ---Dave
> 
> >
> >
> > Best regards,
> > Takayuki Okamoto
> >
> > -----Original Message-----
> > From: gdb-owner@sourceware.org [mailto:gdb-owner@sourceware.org] On
> Behalf Of Dave Martin
> > Sent: Friday, September 1, 2017 2:01 AM
> > To: linux-arm-kernel@lists.infradead.org
> > Cc: Catalin Marinas <catalin.marinas@arm.com>; Will Deacon
> <will.deacon@arm.com>; Ard Biesheuvel <ard.biesheuvel@linaro.org>; Alex
> Bennée <alex.bennee@linaro.org>; Szabolcs Nagy <szabolcs.nagy@arm.com>;
> Richard Sandiford <richard.sandiford@arm.com>;
> kvmarm@lists.cs.columbia.edu; libc-alpha@sourceware.org;
> linux-arch@vger.kernel.org; gdb@sourceware.org; Alan Hayward
> <alan.hayward@arm.com>; Yao Qi <Yao.Qi@arm.com>; Oleg Nesterov
> <oleg@redhat.com>; Alexander Viro <viro@zeniv.linux.org.uk>
> > Subject: [PATCH v2 19/28] arm64/sve: ptrace and ELF coredump support
> >
> 
> [...]
> 
> > @@ -702,6 +737,210 @@ static int system_call_set(struct task_struct
> *target,
> >  	return ret;
> >  }
> >
> > +#ifdef CONFIG_ARM64_SVE
> > +
> > +static void sve_init_header_from_task(struct user_sve_header *header,
> > +				      struct task_struct *target)
> > +{
> > +	unsigned int vq;
> > +
> > +	memset(header, 0, sizeof(*header));
> > +
> > +	header->flags = test_tsk_thread_flag(target, TIF_SVE) ?
> > +		SVE_PT_REGS_SVE : SVE_PT_REGS_FPSIMD;
> > +	if (test_tsk_thread_flag(target, TIF_SVE_VL_INHERIT))
> > +		header->flags |= SVE_PT_VL_INHERIT;
> > +
> > +	header->vl = target->thread.sve_vl;
> > +	vq = sve_vq_from_vl(header->vl);
> > +
> > +	if (WARN_ON(!sve_vl_valid(sve_max_vl)))
> > +		header->max_vl = header->vl;
> > +
> > +	header->size = SVE_PT_SIZE(vq, header->flags);
> > +	header->max_size = SVE_PT_SIZE(sve_vq_from_vl(header->max_vl),
> > +				      SVE_PT_REGS_SVE);
> > +}
> 
> [...]
> 
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