ALIGN in Linker Scripts

Question

What does the ALIGN keyword do in linker scripts? I read many tutorials about linker scripts but I cant understand what really ALIGN do. Can any one explain it simply. Thanks!

Answer 1

A typical usage is

. = ALIGN(8);

This means: insert padding bytes until current location becomes aligned on 8-byte boundary. That is:

while ((current_location & 7) != 0)
  *current_location++ = padding_value;

Answer 2

The ALIGN() instructions tell the linker that section(bss, text) should be this much aligned.

For a typical idea, you can take a look here (4.6.3 "Output Section Description")

e.g.

    //.data is aligned by word size on the 32-bit architecture and direct it to the data section
For a 32-bit machine, it typically needs to be word aligned 

        .data : ALIGN(4) 
        {
           *(.data*)
        } > data_sdram

Answer 3

. = ALIGN(8)

Corresponds to the following (working link script example using operators):

data = .;

. = ((data + 0x8 - 1) & ~(0x8 - 1)) - data;