Various X87 instructions incorrectly print explicit st0 where it should be implicit

[athre0z]

It was brought to my attention by @fvrmatteo that Zydis currently incorrectly prints an explicit st0 for some instructions where it should be implicit / hidden according to Intel SDM. An example of such an instruction is DD 18 alias fstp:

SDM

Zydis

fstp qword ptr ds:[rax], st0

However, this also affects many other X87 instructions. While I originally thought that this would be an easy fix, I later realized that it will require us to reorder the operands for many of these instructions. This is the case because Zydis guarantees that the visible (explicit) operands are first in the operand list, and many users (as well as our own code) rely on that.

For this reason, we decided to postpone this fix until the next major version, Zydis 4.0, in order to comply with our semantic versioning stability guarantee.

XED has the same issue but seems to consider it wontfix: intelxed/xed#162

[williballenthin]

This is the case because Zydis guarantees that the visible (explicit) operands are first in the operand list...

Oh, neat, I didn't realize this. Thanks for mentioning here!