CODEWITHSUNDEEP
windowsassemblyx86nasm
John
John

Reputation: 1119

How to create a variable in the BSS section in NASM?

I tried to create a variable in the BSS section in NASM:

section .bss
    i DD 12345

But when trying to create an object file I got the following warning:

warning: attempt to initialize memory in BSS section `.bss': ignored

Which is understandable I suppose since the BSS section can only contain uninitialized variables. So I attempted the following:

section .bss
    i DD 0

But I still get the same warning.

Upvotes: 5

Views: 7653

Answers (2)

Jester
Jester

Reputation: 58772

Use RESB and friends. See the nasm manual:

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

Upvotes: 6

Arash
Arash

Reputation: 9

The resb and Friends in nasm manual is used to reserve specific amount of bytes in the BSS section of the cod: section .bss Notice that this section must be defined in lowercase (bss) in order not to throw the error. So you may try:

section .bss      ; Create the reservation section.
buffer: resb 128  ; Reserve 128 bites of the memory with label "buffer"

Upvotes: 0

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