.section, .ascii, .quad, .equ are some common directives.string is an alternative to .ascii, here it automatically appends the null byte. .asciz is a synonym
for .string.skip, .space and .zero are used to reserve space with zero or set values of bytes.- For 64-bit systems, speed is fast if access is done on addresses multiple of 8. Some functions use
vector instructions which require 16-byte (128-bit) alignment.
.balign <num> can align the next instruction to the requested number. By default, the spacing
will be zero if you are in a data section or filled with the nop instruction if you are in a
code section. You can also specify, via another parameter, what value to use in the skipped space..p2align is similar to .balign, but takes in the number of bits used for alignment. So for 8
bytes, it would .p2align 3 since 23=8.
Section directives
.text and .data are very common, so you can omit .section for these..rodata, contains data that cannot be modified. Any attempt to modify these values will cause the
program to abort..bss contains uninitialised data. You merely specify the size of the data using .space or .zero.
This saves space in the executable. The OS initialises the bss segment variables to 0.
Local and Global Values
.lcomm is a local directive (local to the file), that can help to initialise a size space with a
given label: .lcomm myvar, 8, reserves space in the .bss section and sets myvar to be the
address of the start of this memory..comm is used for same purpose as .lcomm but it is available to other files as well..external helps you to document that a value is external and the GAS won’t give you error. By default
any undefined values is treated as .global by GAS.
Including other code
.include "filename" directly includes a file into the source code. Note that the included file should
not contain any code or data that are marked as .globl, as that will cause problems when files are linked.
Usually, included files don’t contain any code or data at all..incbin "file" directly includes a file as binary. Commonly used to embedded things like images, other
binaries, bootloaders, fonts, etc.
Annotating directive
.type lets the linker know what kind of symbol is, that is marked by .globl.
.globl myvar, myfunc
.type myvar, @object
.type myfunc, @function