The link-editor defines four built-in segments (text, data, bss and note) with default segment_attribute_values and corresponding default mapping directives. Even though the link-editor does not use an actual mapfile to provide the defaults, the model of a default mapfile helps illustrate what happens when the link-editor encounters your mapfile.
The following example shows how a mapfile would appear for the link-editor defaults. The link-editor begins execution behaving as if the mapfile has already been read in. Then the link-editor reads your mapfile and either augments or makes changes to the defaults.
text = LOAD ?RX; text : ?A!W; data = LOAD ?RWX; data : ?AW; note = NOTE; note : $NOTE;
As each segment declaration in your mapfile is read in, it is compared to the existing list of segment declarations as follows.
If the segment does not already exist in the mapfile but another with the same segment-type value exists, the segment is added before all of the existing segments of the same segment_type.
If none of the segments in the existing mapfile has the same segment_type value as the segment just read in, then the segment is added by segment_type value to maintain the following order.
If the segment is of segment_type LOAD and you have defined a virtual_address value for this LOADable segment, the segment is placed before any LOADable segments without a defined virtual_address value or with a higher virtual_address value, but after any segments with a virtual_address value that is lower.
As each mapping directive in a mapfile is read in, the directive is added after any other mapping directives that you already specified for the same segment but before the default mapping directives for that segment.