Reading DWORD values

NTDEV
1

When examining mouclass code, I noticed following:

// #define WAITWAKE_ON(port) ((port)->WaitWakeIrp != 0)

#define WAITWAKE_ON(port) \
(InterlockedCompareExchangePointer(&(port)->WaitWakeIrp, NULL, NULL)
!= NULL)

I wonder why this change was made; I was under impression reading properly
aligned pointer value is safe with respect to interlocked operations. Is it
false assumption or is it different in 64-bit world?

Best regards,

Michal Vodicka
STMicroelectronics Design and Application s.r.o.
[michal.vodicka@st.com, http:://www.st.com]

2

I was being overly aggressive, a normal read would have been fine.

d

-----Original Message-----
From: xxxxx@lists.osr.com
[mailto:xxxxx@lists.osr.com] On Behalf Of Michal Vodicka
Sent: Friday, February 13, 2004 12:48 PM
To: Windows System Software Devs Interest List
Subject: [ntdev] Reading DWORD values

When examining mouclass code, I noticed following:

// #define WAITWAKE_ON(port) ((port)->WaitWakeIrp != 0)

#define WAITWAKE_ON(port) \
(InterlockedCompareExchangePointer(&(port)->WaitWakeIrp, NULL,
NULL)
!= NULL)

I wonder why this change was made; I was under impression reading
properly
aligned pointer value is safe with respect to interlocked operations. Is
it
false assumption or is it different in 64-bit world?

Best regards,

Michal Vodicka
STMicroelectronics Design and Application s.r.o.
[michal.vodicka@st.com, http:://www.st.com]

Questions? First check the Kernel Driver FAQ at
http://www.osronline.com/article.cfm?id=256

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