FillUserMemory function (usermode_accessors.h)

The FillUserMemory function fills a user-mode memory region with a specified byte value.

Syntax

void FillUserMemory(
  volatile VOID *Destination,
  SIZE_T        Length,
  UCHAR         Fill
);

Parameters

Destination

[out] A pointer to the starting address of the memory block to fill.

Length

[in] The number of bytes to fill with the Fill value.

Fill

[in] The byte value used to fill the first Length bytes of Destination.

Return value

None

Remarks

This function provides a safe way to fill a user-mode memory region with a specified byte value. This allows for flexible memory operations when kernel-mode code needs to initialize user-mode memory buffers.

The function has the following properties:

• The function performs a fill using memory_order_relaxed semantics.

• The function isn't recognized as a compiler intrinsic so the compiler will never optimize away the call (either entirely or replace the call with an equivalent sequence of instructions).

• When the call returns, the buffer has been overwritten with the specified Fill value. This function's memory accesses to the Destination will only be performed within the function (for example, the compiler can't move memory accesses out of this function).

• The function might perform unaligned memory accesses if the platform allows for it.

• The function might access memory locations more than once as part of its fill operation.

The function raises a structured exception if the fill operation fails, such as when the destination address is not a valid user-mode address or is inaccessible.

This function works on all versions of Windows, not just the latest. You need to consume the latest WDK to get the function declaration from the usermode_accessors.h header. You also need the library (umaccess.lib) from the latest WDK. However, the resulting driver will run fine on older versions of Windows.

Requirements

See also

FillModeMemory

SetUserMemory

ZeroUserMemory

CopyToUser