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0 pointshyperman15y ago0 comments

x86 had a few undocumented opcodes. AAD and AAM have a second byte that should always be 10, but turns out to be an argument for base10 . There was salc.

A CPU, when it encounters bytes in its instruction stream, has to do something, whatever. If there is no interrupt for invalid instruction, it has to do something else. Common behaviour is shadowing legal insn's , but completely new behaviour is always possible

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rbanffy5y ago

Actually doing something useful on invalid opcodes is cool, but a bad long-term idea - you'll end up having to support all the accidental behavior that ends up being used forever, or risk breaking backwards compatibility.

j / k navigate · click thread line to collapse

0 pointshyperman15y ago0 comments

x86 had a few undocumented opcodes. AAD and AAM have a second byte that should always be 10, but turns out to be an argument for base10 . There was salc.

0 comments

rbanffy5y ago

j / k navigate · click thread line to collapse