WriteStructToUserAligned macro (usermode_accessors.h)

The WriteStructToUserAligned macro safely writes a structure to user-mode memory with alignment validation.

Syntax

void WriteStructToUserAligned(
   Destination,
   Source,
   Alignment
);

Parameters

Destination

[out] A pointer to the user-mode memory location where the structure will be written.

Source

[in] A pointer to the structure to write to the destination memory location.

Alignment

[in] The required alignment for the destination address, in bytes.

Return value

None

Remarks

This macro provides a safe way to write a structure to user-mode memory with alignment enforcement. It ensures the provided address is a user-mode address and meets the specified alignment requirements before writing to it.

The macro validates that Source and Destination point to compatible types and automatically determines the structure size for the copy operation.

This macro enforces alignment by verifying that the destination address meets the specified alignment requirement. This helps prevent performance penalties and potential hardware faults that can occur when accessing misaligned data structures.

It raises a structured exception if the memory access fails, such as when the destination address isn't a user-mode address, is inaccessible, or doesn't meet the alignment requirements.

This macro will never be optimized away by the compiler, nor will the compiler create additional accesses to this memory location before the macro is called or after the macro returns (unless the source code explicitly performs these accesses). The memory access is performed with memory_order_relaxed semantics.

This macro works on all versions of Windows, not just the latest. You need to consume the latest WDK to get the macro 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

WriteStructToUser

WriteStructToModeAligned

WriteStructToUserHelper

ReadStructFromUserAligned