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<== Date ==> <== Thread ==>

Subject: Re: C strict aliasing rules
From: Kay-Uwe Kasemir <kasemirk@ornl.gov>
To: Core talk list <core-talk@aps.anl.gov>
Date: Tue, 28 Nov 2006 09:33:40 -0500
Hi:

Do I understand correctly that the most likely impact for EPICS might be this type of code:

struct xyz_regs
{
    Word control;
    Word status;
    ...
}

void xyz_operate(char *vme_base)
{
    struct xyz_regs *xyz = (struct xyz_regs *) vme_base;

    xyz->control = 0x1234;
    if (xyz->status & 0x8000)
      ....
}

The mapping of C structures to hardware registers?
In that case, the compiler optimization of aliased pointers
isn't the only problem. There's also the structure padding,
memory alignment, and byte order that causes portability issues.

Isn't that best handled by performing register access
via routines like the vxWorks sysInByte(), sysInWord(), sysInLong(), sysPciInLong(), ... ?

-Kay

Replies:
Re: C strict aliasing rules Eric Norum
Re: C strict aliasing rules Marty Kraimer
References:
C strict aliasing rules Eric Norum
Re: C strict aliasing rules Benjamin Franksen
Re: C strict aliasing rules Eric Norum
Re: C strict aliasing rules Benjamin Franksen

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