From: Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
To: Vineet Gupta <Vineet.Gupta1@synopsys.com>
Cc: "paltsev@snyopsys.com" <paltsev@snyopsys.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Alexey Brodkin <Alexey.Brodkin@synopsys.com>,
"linux-snps-arc@lists.infradead.org"
<linux-snps-arc@lists.infradead.org>
Subject: Re: [PATCH 4/9] ARC: mm: do_page_fault refactor #3: tidyup vma access permission code
Date: Fri, 17 May 2019 22:23:40 +0000 [thread overview]
Message-ID: <1558131743.2682.33.camel@synopsys.com> (raw)
In-Reply-To: <C2D7FE5348E1B147BCA15975FBA2307501A2517B16@us01wembx1.internal.synopsys.com>
Hmmm,
so load the bool variable from memory is converted to such asm code:
----------------->8-------------------
ldb r2,[some_bool_address]
extb_s r2,r2
----------------->8-------------------
Could you please describe that the magic is going on there?
This extb_s instruction looks completely useless here, according on the LDB description from PRM:
----------------->8-------------------
LD LDH LDW LDB LDD:
The size of the requested data is specified by the data size field <.zz> and by default, data is zero
extended from the most-significant bit of the data to the most-significant bit of the destination
register.
----------------->8-------------------
Am I missing something?
On Thu, 2019-05-16 at 17:37 +0000, Vineet Gupta wrote:
> On 5/16/19 10:24 AM, Eugeniy Paltsev wrote:
> > > + unsigned int write = 0, exec = 0, mask;
> >
> > Probably it's better to use 'bool' type for 'write' and 'exec' as we really use them as a boolean variables.
>
> Right those are semantics, but the generated code for "bool" is not ideal - given
> it is inherently a "char" it is promoted first to an int with an additional EXTB
> which I really dislike.
> Guess it is more of a style thing.
>
> -Vineet
--
Eugeniy Paltsev
next prev parent reply other threads:[~2019-05-17 22:23 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-15 0:29 [PATCH 0/9] ARC do_page_fault rework Vineet Gupta
2019-05-15 0:29 ` [PATCH 1/9] ARC: mm: SIGSEGV userspace trying to access kernel virtual memory Vineet Gupta
2019-05-15 0:29 ` [PATCH 2/9] ARC: mm: do_page_fault refactor #1: remove label @good_area Vineet Gupta
2019-05-15 0:29 ` [PATCH 3/9] ARC: mm: do_page_fault refactor #2: remove short lived variable Vineet Gupta
2019-05-15 0:29 ` [PATCH 4/9] ARC: mm: do_page_fault refactor #3: tidyup vma access permission code Vineet Gupta
2019-05-16 17:24 ` Eugeniy Paltsev
2019-05-16 17:37 ` Vineet Gupta
2019-05-16 17:44 ` Alexey Brodkin
2019-05-16 18:57 ` Vineet Gupta
2019-05-17 22:23 ` Eugeniy Paltsev [this message]
2019-05-30 17:58 ` extraneous generated EXTB (was Re: [PATCH 4/9] ARC: mm: do_page_fault refactor #3: tidyup vma access permission code) Vineet Gupta
2019-05-15 0:29 ` [PATCH 5/9] ARC: mm: do_page_fault refactor #4: consolidate retry related logic Vineet Gupta
2019-05-15 0:29 ` [PATCH 6/9] ARC: mm: do_page_fault refactor #5: scoot no_context to end Vineet Gupta
2019-05-15 0:29 ` [PATCH 7/9] ARC: mm: do_page_fault refactor #6: error handlers to use same pattern Vineet Gupta
2019-05-15 0:29 ` [PATCH 8/9] ARC: mm: do_page_fault refactor #7: fold the various error handling Vineet Gupta
2019-05-15 0:29 ` [PATCH 9/9] ARC: mm: do_page_fault refactor #8: release mmap_sem sooner Vineet Gupta
2019-05-30 16:48 ` Vineet Gupta
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