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3.10.3 The Location Counter

The special linker variable dot `.' always contains the current output location counter. Since the . always refers to a location in an output section, it may only appear in an expression within a SECTIONS command. The . symbol may appear anywhere that an ordinary symbol is allowed in an expression.

Assigning a value to . will cause the location counter to be moved. This may be used to create holes in the output section. The location counter may never be moved backwards.

  output :
      . = . + 1000;
      . += 1000;
    } = 0x12345678;
In the previous example, the `.text' section from `file1' is located at the beginning of the output section `output'. It is followed by a 1000 byte gap. Then the `.text' section from `file2' appears, also with a 1000 byte gap following before the `.text' section from `file3'. The notation `= 0x12345678' specifies what data to write in the gaps (see section Output section fill).

Note: . actually refers to the byte offset from the start of the current containing object. Normally this is the SECTIONS statement, whoes start address is 0, hence . can be used as an absolute address. If . is used inside a section description however, it refers to the byte offset from the start of that section, not an absolute address. Thus in a script like this:

    . = 0x100
    .text: {
      . = 0x200
    . = 0x500
    .data: {
      . += 0x600

The `.text' section will be assigned a starting address of 0x100 and a size of exactly 0x200 bytes, even if there is not enough data in the `.text' input sections to fill this area. (If there is too much data, an error will be produced because this would be an attempt to move . backwards). The `.data' section will start at 0x500 and it will have an extra 0x600 bytes worth of space after the end of the values from the `.data' input sections and before the end of the `.data' output section itself.

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