Article: AMD's Mobile Strategy
By: Exophase (exophase.delete@this.gmail.com), December 21, 2011 11:12 pm
Room: Moderated Discussions
anonymous (no@spam.com) on 12/21/11 wrote:
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>In x86-64's 64-bit mode the near branches default to 64-bit operand size
>but use a sign-extended 32-bit displacement. Currently adding a REX.W=1
>prefix does nothing. All that's needed is a minor re-definition: with W=1 a
>near branch could be followed by a sign-extended 64-bit displacement. :)
>
>Yes, such 64-bit near branches would be long, i.e. impact the decoder. But
>at least they would let me branch without trampolines, which are far worse.
I meant memory displacements, not branches. No idea why there's no option for 64-bit displacements through REX.
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>In x86-64's 64-bit mode the near branches default to 64-bit operand size
>but use a sign-extended 32-bit displacement. Currently adding a REX.W=1
>prefix does nothing. All that's needed is a minor re-definition: with W=1 a
>near branch could be followed by a sign-extended 64-bit displacement. :)
>
>Yes, such 64-bit near branches would be long, i.e. impact the decoder. But
>at least they would let me branch without trampolines, which are far worse.
I meant memory displacements, not branches. No idea why there's no option for 64-bit displacements through REX.