NASB中RESB，RESW，RESD，RESQ分配多少字节? [英] How much bytes does RESB, RESW, RESD, RESQ allocates in NASM?

问题描述

DB分配1个字节.

DW分配2个字节.

DD分配4个字节.

DQ分配8个字节.

所以我认为:

RESB 1分配1个字节.

RESW 1分配2个字节.

RESD 1分配4个字节.

RESQ 1分配8个字节.

我正确吗?

---

文档没有"不多说:

3.2.2 RESB和朋友:声明未初始化的数据

RESB，RESW，RESD，RESQ，REST，RESO，RESY和RESZ设计为 在模块的BSS部分中使用:它们声明未初始化 储存空间.每个都采用一个操作数，即 字节，字，双字或任何保留字.如本节所述 2.2.7，NASM不支持通过编写DW?保留未初始化空间的MASM/TASM语法.或类似的东西:这就是它 相反. RESB型伪指令的操作数是 批判性表达:请参见3.8节.

例如:

缓冲区:resb 64；保留64个字节

wordvar:resw 1;保留一个字词

realarray resq 10;十个实数的数组

ymmval:resy 1；一个YMM寄存器

zmmvals:resz 32； 32个ZMM寄存器

解决方案

我正确吗?

是.

对于d*和res*，整个NASM的大小后缀都是一致的.它们将x86指令助记符后缀匹配为字节到qword. (例如psubd适用于打包的dword元素).

甚至还有使用o(八字)的指令助记符: cqo .

y和z大小的后缀显然与ymm和zmm寄存器的大小匹配，即使指令助记符现在类似于 VBROADCASTI32X8 ，因为AVX512的屏蔽粒度.

DB allocates 1 byte.

DW allocates 2 bytes.

DD allocates 4 bytes.

DQ allocates 8 bytes.

So I assume that:

RESB 1 allocates 1 byte.

RESW 1 allocates 2 bytes.

RESD 1 allocates 4 bytes.

RESQ 1 allocates 8 bytes.

Am I correct?

---

The documentation doesn't say much:

3.2.2 RESB and Friends: Declaring Uninitialized Data

RESB, RESW, RESD, RESQ, REST, RESO, RESY and RESZ are designed to be used in the BSS section of a module: they declare uninitialized storage space. Each takes a single operand, which is the number of bytes, words, doublewords or whatever to reserve. As stated in section 2.2.7, NASM does not support the MASM/TASM syntax of reserving uninitialized space by writing DW ? or similar things: this is what it does instead. The operand to a RESB-type pseudo-instruction is a critical expression: see section 3.8.

For example:

buffer: resb 64 ; reserve 64 bytes

wordvar: resw 1 ; reserve a word

realarray resq 10 ; array of ten reals

ymmval: resy 1 ; one YMM register

zmmvals: resz 32 ; 32 ZMM registers

解决方案

Am I correct?

yes.

The size suffixes are consistent throughout NASM, for d* and res*. They match x86 instruction mnemonic suffixes for byte to qword. (e.g. psubd works with packed dword elements).

There's even an instruction mnemonic that uses o (oct-word): cqo.

y and z size suffixes obviously match ymm and zmm register sizes, even though the instruction mnemonics are now things like VBROADCASTI32X8 because of AVX512 masking granularity.

这篇关于NASB中RESB，RESW，RESD，RESQ分配多少字节?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！