How much bytes does RESB, RESW, RESD, RESQ allocat

Question

This question already has an answer here:

• What are the sizes of tword, oword and yword operands? 2 answers

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?

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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

Answer 1

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.