linux-kernel - Re: [RFC] Coverity 1128445 - Reliance on integer endianness

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Message-ID: <yw1xd2m5vg9j.fsf@unicorn.mansr.com>
Date:	Tue, 12 Nov 2013 14:36:24 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Geyslan Gregório Bem <geyslan@...il.com>
Cc:	a.p.zijlstra@...llo.nl, paulus@...ba.org,
	Ingo Molnar <mingo@...hat.com>, acme@...stprotocols.net,
	kernel-br <kernel-br@...glegroups.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] Coverity 1128445 - Reliance on integer endianness

Geyslan Gregório Bem <geyslan@...il.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@...sr.com
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