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NASM Forum => Other Discussion => Topic started by: shaynox on June 14, 2015, 06:40:26 PM

Title: [Bug] rep instruction
Post by: shaynox on June 14, 2015, 06:40:26 PM

I found a bug, nasm don't detect this error (not mov):

Code: [Select]

            mov     rcx, 1
            rep     vmovups     ymm0, ymm0

In manual of intel it's false but even so by curiosity I run this block of code and it crash (unfortunately x) )

Title: Re: [Bug] rep instruction
Post by: encryptor256 on June 14, 2015, 07:41:49 PM

Quote from: shaynox on June 14, 2015, 06:40:26 PM

I found a bug, nasm don't detect this error (not mov):

Code: [Select]

            mov     rcx, 1
            rep     vmovups     ymm0, ymm0

In manual of intel it's false but even so by curiosity I run this block of code and it crash (unfortunately x) )

Nice catch, shaynox!

I wouldn't call it: "error".
REP is a prefix and looks like - is not affecting rest of the instruction bits n bytes.
But that's right: "nasm don't detect".
But maybe you can find some applications for this permission to add REP prefixes.

Quote from: shaynox on June 14, 2015, 06:40:26 PM

I run this block of code and it crash (unfortunately x) )

Interesting... Then what kind of result you were expecting?

Title: Re: [Bug] rep instruction
Post by: shaynox on June 14, 2015, 07:44:02 PM

Thanks ^^

Nothing, it just crash, I don't know what kind of error, windows ask to me if I want to debug but no time for that

And if I run this instruction on my OS, I think than it will make a reset of CPU.