SetModeMemory function (usermode_accessors.h)

The SetModeMemory function fills a memory region with a specified byte value, based on the specified processor mode.

Syntax

void SetModeMemory(
  VOID            *Destination,
  UCHAR           Fill,
  SIZE_T          Length,
  KPROCESSOR_MODE Mode
);

Parameters

Destination

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

Fill

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

Length

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

Mode

[in] The processor mode that determines how the memory access is performed. Mode can be one of the following values.

Return value

None

Remarks

This function provides a safe way to fill a memory region with a specified byte value, with the fill mechanism determined by the specified processor mode.

The function has the following properties:

• When Mode is KernelMode, the function performs a direct memory fill without additional safety checks.

• When Mode is UserMode, the function validates the pointer is a user-mode address and then performs the fill. The memory access is performed with memory_order_relaxed semantics.

• This function isn't recognized as a compiler instrinsic 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 first Length bytes of the buffer have 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 valid for the specified mode 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

SetUserMemory

FillModeMemory

ZeroModeMemory

CopyToMode