Re: byte alignment/dynamic memory from heap x64

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Ivan,

Thank you very much for the education on this topic, it helped me resolve
and understand my problem.

Mike

"Ivan Brugiolo [MSFT]" wrote:

The 16-byte alignment for SLIST_HEADER applies only to x64/IA64, and, on
those platforms,
pool allocations are always 16-bytes aligned.
As long as your structure is `casted` directly from the returned value from
ExAllocatePool[*],
and, you do not change the declaration of SLIST_HEADER in the WDK/DDK
headers,
the compiler will take care of that for you.
For example, this will prove the compiler right or wrong.

typedef struct _Align16 {
BYTE OneChar;
SLIST_HEADER Header;
} Align16;

C_ASSERT(FIELD_OFFSET(Align16,Header) == 0x10);

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"Mike L" <MikeL@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:5211EC28-341F-4607-96C6-B7ACB0B2D103@xxxxxxxxxxxxxxxx

My IM driver uses SLIST_ENTRY and SLIST_HEADER(s) and they are declared in
a
struct and when my driver is loaded I dynamically allocate memory using
these
structs.

for example(not my real struct...)

struct X {

int y;
PNDIS_BUFFER pBuf;
....
SLIST_HEADER ListHeader;
SLIST_ENTRY ListEntry;
...
};

The documention for x64 states that SLIST_ENTRY and SLIST_HEADER must be
16
byte aligned.

How do I force this to happen ?

I have tried the below 3 methods( and with all 3 methods the byte
alignment
seems also to be 8 bytes instead of 16):

1) Method 1 - ExAllocatePoolWithTag with NonPagedPoolCacheAligned
2) Method 2 - pragma pack(push, 16)
3) __declspec(align(16)) - Documentation states that this will not work
for
dynamic memory from the heap, so I assume that is why it didn't work.

Any advice is appreciated, I might have a bug in my code for one of the
above methods, so I really just need someone to tell me how this is
normally
done and I can figure out the details. I saw another function
_align_memory, but did not want to link an NDIS driver to the c runtime
for
memory management, but maybe that is another alternative.

thanks,
Mike






.

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