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(ld.info)Location Counter

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Enter node , (file) or (file)node

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.

     SECTIONS
     {
       output :
         {
           file1(.text)
           . = . + 1000;
           file2(.text)
           . += 1000;
           file3(.text)
         } = 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 (Note:
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:

     SECTIONS
     {
         . = 0x100
         .text: {
           *(.text)
           . = 0x200
         }
         . = 0x500
         .data: {
           *(.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.