The same happens in reverse when coming back. They proxy all kernel calls from 32bit code and then segment switch to a 64bit segment before calling the kernel. That's all handled via WoW64CPU.dll and friends.
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The kernel doesn't actually care whether the user space application is 32 bit or 64bit in many cases. While they are migrating it's not a quick process in many cases.Īs for 16bit HANDLEs for 32bit programs, it wouldn't have solved the issue as the HANDLEs are kernel tokens. Most of the people that care however are large legacy enterprises that are running line of business applications that they don't have the source code for or require libraries they don't have the source code for. So unfortunately people do care, it's why 32bit windows is still a thing. In 64bit mode this isn't the case because there are no FAR pointers and segmentation. So they could operate in the same address space. In the end it was easier to just ship a 32bit version of windows for those that still needed that support.ġ^ This was only possible because FAR pointers in 16bit mode are still 32 bits and thus size of a pointer was in effect the same. Nor is it like MS could emulate this like the OPs code does, because that would require rewriting applications that had already shipped from ISVs that don't exist anymore or magically understanding when an application has 16bit code and needs to get fake HANDLEs neither of which is easy in reality. So a HANDLE passed to 16bit code wouldn't round trip correctly due to truncation. expanding the limits on programs to be less restrictive, it was always going to have something to give.īecause 32bit code often "thunked"^1 in 16bit code they couldn't really support it because even in 32bit mode HANDLEs still have 32bits of valid HANDLE. So unless Microsoft wanted to completely negate the value of going to 64bit in the first place, e.g.
HANDLEs on 64bit windows have 32bits that are valid whereas HANDLES on 32bit windows only have 16bits that are valid. It was a deliberate design decision for technical reasons (. This is the limit of their famous backwards compatibility - still impressive, though.
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It was a political choice by Microsoft to drop 16 bit Windows support in 64 bit Windows.
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