I wrote uefi app and it get compiled successfully but when I used qemu to test it, I got incorrect numbers amount of memory (256 MB).

definition of EFI_MEMORY_DESCRIPTOR:

///
/// Definition of an EFI memory descriptor.
///
typedef struct {
  ///
  /// Type of the memory region.
  /// Type EFI_MEMORY_TYPE is defined in the
  /// AllocatePages() function description.
  ///
  UINT32                  Type;
  ///
  /// Physical address of the first byte in the memory region. PhysicalStart must be
  /// aligned on a 4 KiB boundary, and must not be above 0xfffffffffffff000. Type
  /// EFI_PHYSICAL_ADDRESS is defined in the AllocatePages() function description
  ///
  EFI_PHYSICAL_ADDRESS    PhysicalStart;
  ///
  /// Virtual address of the first byte in the memory region.
  /// VirtualStart must be aligned on a 4 KiB boundary,
  /// and must not be above 0xfffffffffffff000.
  ///
  EFI_VIRTUAL_ADDRESS     VirtualStart;
  ///
  /// NumberOfPagesNumber of 4 KiB pages in the memory region.
  /// NumberOfPages must not be 0, and must not be any value
  /// that would represent a memory page with a start address,
  /// either physical or virtual, above 0xfffffffffffff000.
  ///
  UINT64                  NumberOfPages;
  ///
  /// Attributes of the memory region that describe the bit mask of capabilities
  /// for that memory region, and not necessarily the current settings for that
  /// memory region.
  ///
  UINT64                  Attribute;
} EFI_MEMORY_DESCRIPTOR;

Code:

UINT64
GMS(EFI_MEMORY_DESCRIPTOR* MMap, UINT64 MMAPE, UINT64 MMAPDESCSIZE)
{
    static UINT64 MemSizeB = 0;
    if (MemSizeB > 0) return MemSizeB;

    for (unsigned int i = 0; i < MMAPE; i++){
        EFI_MEMORY_DESCRIPTOR *desc = (EFI_MEMORY_DESCRIPTOR*)((UINT64*)MMap + i * MMAPDESCSIZE);
        MemSizeB += desc->NumberOfPages * EFI_PAGE_SIZE;
    }

    return MemSizeB;
}


EFI_STATUS
EFIAPI
UefiMain (
  IN EFI_HANDLE ImageHandle,
  IN EFI_SYSTEM_TABLE *SystemTable
  )
{

    EFI_MEMORY_DESCRIPTOR* Map = NULL;
    UINTN MapSize, MapKey, DescSize;
    UINT32 DescVer;
    {
        SystemTable->BootServices->GetMemoryMap(&MapSize, Map, &MapKey, &DescSize, &DescVer);
        SystemTable->BootServices->AllocatePool(EfiLoaderData, MapSize, (void**)&Map);
        SystemTable->BootServices->GetMemoryMap(&MapSize, Map, &MapKey, &DescSize, &DescVer);
    }

    UINT64 MapEntries = MapSize / DescSize;
    Print(L"Map Entries: %dn", MapEntries);
    Print(L"Map Size: %dn", MapSize);
    Print(L"Descriptor Size: %dn", DescSize);



    Print(L"Size of memory: %dn", GMS(Map, MapEntries, DescSize));


    return EFI_SUCCESS;
}

I use GCC for compiling and edk2 (edk2-stable202411) for creating UEFI app.

Big thank to someone who could help me

tried using EFI_PAGE_SIZE but problem didn’t quit