What does ntdll_77bc0000 or ntdll_772d0000 means in Wow64 call stack

I have WOW64 crash dumps with call stack information like:

0018fb00 77c06a8b 0018fbc8 0018ffc4 0018fc18 ntdll_77bc0000!ExecuteHandler2+0x26

or like:

0018fb00 77c06a8b 0018fbc8 0018ffc4 0018fc18 ntdll_772d0000!ExecuteHandler2+0x26

The ntdll_772d0000 seems to be a dll name, but I didn't see it in C:\Windows\SysWOW64, and I am also curious why there might be different names like ntdll_77bc0000 and ntdll_772d0000 on the same machine.

Thanks.开发者_运维技巧

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these are multiple copies of ntdll loaded at alternate (as opposed to preferred) base addresses.