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 (see Output Section Fill).
Note: .
actually refers to the byte offset from the start of the
current containing object. Normally this is the SECTIONS
statement, whose 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.