5 Matching Annotations
- Jan 2022
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tvrctkmytfln.gitee.io tvrctkmytfln.gitee.io
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If one of those two expressions couldpossibly generate an error condition or a side effect, this could lead to invalidbehavior. Such is the case for our earlier example
有什么情况下必须使用 branching 方式,而不能使用 conditional move?
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- Nov 2021
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tvrctkmytfln.gitee.io tvrctkmytfln.gitee.io
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One important feature is that memoryreferences in x86-64 are always given with quad word registers, such as %rax, evenif the operand is a byte, single word, or double word.
memory reference 属于那种 register 类型?
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logicallybe named movzlq, but this instruction does not exist. Instead, this type of datamovement can be implemented using a movl instruction having a register as thedestination. This technique takes advantage of the property that an instructiongenerating a 4-byte value with a register as the destination will fill the upper 4bytes with zeros.
为什么在 movz 的指令中缺少 movzlq?
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in memory, to a register destination. Instructions in the movz class fill out theremaining bytes of the destination with zeros, while those in the movs class fillthem out by sign extension, replicating copies of the most significant bit of thesource operand.
那两种 move 指令针对 copy smaller source 到 larger destination,他们的做法分别是什么?
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The source operand designates a value that is immediate, stored in a register,or stored in memory. The destination operand designates a location that is either aregister or a memory address. x86-64 imposes the restriction that a move instruc-tion cannot have both operands refer to memory locations. Copying a value fromone memory location to another requires two instructions—the first to load thesource value into a register, and the second to write this register value to the des-tination.
move 的 source operand 和 destination operand 分别可以是哪些类型?
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