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From: =?iso-8859-1?Q?M=E5ns_Rullg=E5rd?= <mans@mansr.com>
To: Geyslan =?iso-8859-1?Q?Greg=F3rio?= Bem <geyslan@gmail.com>
Cc: a.p.zijlstra@chello.nl, paulus@samba.org, Ingo Molnar <mingo@redhat.com>,
        acme@ghostprotocols.net, kernel-br <kernel-br@googlegroups.com>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] Coverity 1128445 - Reliance on integer endianness
References: <CAGG-pUQrN6D_iSsWVptjQSA4B_oGn5NhbhBp+aLT0GJCFSmYRA@mail.gmail.com>
Date: Tue, 12 Nov 2013 14:36:24 +0000
In-Reply-To: <CAGG-pUQrN6D_iSsWVptjQSA4B_oGn5NhbhBp+aLT0GJCFSmYRA@mail.gmail.com>
	("Geyslan =?iso-8859-1?Q?Greg=F3rio?= Bem"'s message of "Tue, 12 Nov 2013
 12:19:13
	-0200")
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Geyslan Gregório Bem <geyslan@gmail.com> writes:

> Hi,
>
> Coverity detected in 'arch/x86/kernel/cpu/perf_event_intel_uncore.c' a
> possible reliance on integer endianness. Is that a positive one?

No, x86 is always little endian.

> static u64 ivt_uncore_irp_read_counter(struct intel_uncore_box *box,
> struct perf_event *event)
> 1369{
> 1370        struct pci_dev *pdev = box->pci_dev;
> 1371        struct hw_perf_event *hwc = &event->hw;
> 1372        u64 count = 0;
> 1373
>
> CID 1128445 (#1 of 1): Reliance on integer endianness
> (INCOMPATIBLE_CAST)incompatible_cast: Pointer "&count" points to an
> object whose effective type is "unsigned long long" (64 bits,
> unsigned) but is dereferenced as a narrower "unsigned int" (32 bits,
> unsigned). This may lead to unexpected results depending on machine
> endianness.[show details]
>
> 1374        pci_read_config_dword(pdev, ivt_uncore_irp_ctrs[hwc->idx],
> (u32 *)&count);
> 1375        pci_read_config_dword(pdev, ivt_uncore_irp_ctrs[hwc->idx]
> + 4, (u32 *)&count + 1);
> 1376
> 1377        return count;
> 1378}

This looks intentional and correct apart from possible strict aliasing
issues.

-- 
Måns Rullgård
mans@mansr.com