linux-kernel - Re: [PATCH v1 8/8] ACPI: Use recently introduced uuid_le_cmp

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Date:   Thu, 27 Apr 2017 16:09:56 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Borislav Petkov <bp@...e.de>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Lukas Wunner <lukas@...ner.de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        alsa-devel@...a-project.org, linux-input@...r.kernel.org,
        kvm@...r.kernel.org, devel@...uxdriverproject.org,
        linux-efi@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v1 8/8] ACPI: Use recently introduced uuid_le_cmp_p{p}()
 helpers

On Thu, 2017-04-27 at 14:46 +0200, Borislav Petkov wrote:
> On Fri, Apr 21, 2017 at 11:22:31PM +0200, Rafael J. Wysocki wrote:
> > >  #ifdef CONFIG_ACPI_APEI_PCIEAER
> > > -		else if (!uuid_le_cmp(*(uuid_le *)gdata-
> > > >section_type,
> > > -				      CPER_SEC_PCIE)) {
> > > +		else if (!uuid_le_cmp_p(sec_type, CPER_SEC_PCIE))
> > > {
> > >  			struct cper_sec_pcie *pcie_err;
> > >  			pcie_err = (struct cper_sec_pcie
> > > *)(gdata+1);
> > >  			if (sev == GHES_SEV_RECOVERABLE &&
> > > 
> > 
> > But this one is for Boris.
> 
> I don't see anything wrong with it upon a brief inspection.

Lukas pointed to this:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68725

> 
> What could be improved here, though, is if the whole uuid_* types
> handling be changed so that gcc doesn't generate yucky code. Because
> here's what it does now, regardless of this patch:
> 
>         .file 16 "./include/linux/uuid.h"
>         .loc 16 63 0
>         leaq    16(%rsp), %rsi  #,
>         movl    $16, %edx       #,
>         movq    %r15, %rdi      # gdata,
>         movb    $84, 16(%rsp)   #, MEM[(struct  *)&u2]
>         movb    $-23, 17(%rsp)  #, MEM[(struct  *)&u2 + 1B]
>         movb    $-107, 18(%rsp) #, MEM[(struct  *)&u2 + 2B]
>         movb    $-39, 19(%rsp)  #, MEM[(struct  *)&u2 + 3B]
>         movb    $-63, 20(%rsp)  #, MEM[(struct  *)&u2 + 4B]
>         movb    $-69, 21(%rsp)  #, MEM[(struct  *)&u2 + 5B]
>         movb    $15, 22(%rsp)   #, MEM[(struct  *)&u2 + 6B]
>         movb    $67, 23(%rsp)   #, MEM[(struct  *)&u2 + 7B]
>         movb    $-83, 24(%rsp)  #, MEM[(struct  *)&u2 + 8B]
>         movb    $-111, 25(%rsp) #, MEM[(struct  *)&u2 + 9B]
>         movb    $-76, 26(%rsp)  #, MEM[(struct  *)&u2 + 10B]
>         movb    $77, 27(%rsp)   #, MEM[(struct  *)&u2 + 11B]
>         movb    $-53, 28(%rsp)  #, MEM[(struct  *)&u2 + 12B]
>         movb    $60, 29(%rsp)   #, MEM[(struct  *)&u2 + 13B]
>         movb    $111, 30(%rsp)  #, MEM[(struct  *)&u2 + 14B]
>         movb    $53, 31(%rsp)   #, MEM[(struct  *)&u2 + 15B]
>         call    memcmp  #
> 
> So it is basically building that UUID byte by byte before calling
> memcmp.
> 
> And I'm wondering if those 16-byte arrays could be replaced with
> 
> typedef struct {
>         u64 a, b;
> } u128;
> 
> from the crypto code.
> 
> And whether the code generated by gcc would look much saner. Because
> the
> CPU can handle two qwords much better/faster than 16 u8s.
> 
> Anyway, in case someone feels bored...
> 
> -- 
> Regards/Gruss,
>     Boris.
> 
> SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton,
> HRB 21284 (AG Nürnberg)

-- 
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Intel Finland Oy