Mapping example

``User-Defined Mapfile'' is an example of a user-defined mapfile. The numbers on the left are included in the example for tutorial purposes. Only the information to the right of the numbers would actually appear in the mapfile.

1.	elephant : .bss : peanuts.o popcorn.o;
2.	monkey : $PROGBITS ?AX;
3.	monkey : .bss;
4.	monkey = LOAD V0x80000000 L0x4000;
5.	monkey = LOAD;
6.	donkey = ?RWX;
7.	donkey : .bss;
8.	donkey = ?RX A0x1000;
9.	text = ?RWX V0x80008000;

User-Defined Mapfile

Four separate segments are manipulated in this example. The implicitly declared segment elephant (line 1) receives all of the .bss sections from the files peanuts.o and popcorn.o. Note that popcorn.o matches any popcorn.o file that may have been entered on the ld command line; the file need not be in the current directory. On the other hand, if /var/tmp/peanuts.o were entered on the ld command line, it would not match peanuts.o because it is not preceded by a .

The implicitly declared segment monkey (line 2) receives all sections that are both $PROGBITS and allocatable-executable (?AX), as well as all sections (not already in the segment elephant) with the name .bss (line 3). The .bss sections entering the monkey segment need not be $PROGBITS or allocatable-executable because the section_type and section_flags values were entered on a separate line from the section_name value. (An "and" relationship exists between attributes on the same line as illustrated by $PROGBITS "and" ?AX on line 2. An "or" relationship exists between attributes for the same segment that span more than one line as illustrated by $PROGBITS ?AX on line 2 "or" .bss on line 3.)

The monkey segment is implicitly declared in line 2 with segment_type value LOAD, segment_flags value ?RWX, and default virtual_address, physical_address, length, and alignment values specified per CPU type. In line 4 the segment_type value of monkey is set to LOAD, virtual_address value to 0x80000000 and maximum length value to 0x4000. In line 5 the segment_type value of monkey is again set to LOAD (since the segment_type attribute value does not change, no warning is issued).

Line 6 implicitly declares the donkey segment. The entrance criteria is designed to route all .bss sections to this segment. Actually, no sections fall into this segment because the entrance criteria for monkey in line 3 capture all of these sections. In line 8, the segment_flags value is set to ?RX and the alignment value is set to 0x1000 (since the segment_flags value changes, a warning is issued).

Line 9 changes the segment_flags value to ?RWX and the virtual_address value of the text segment to 0x80008000 (since the segment_flags value changes, a warning is issued).

The example user-defined mapfile in

``User-Defined Mapfile'' is designed to cause warnings for illustration purposes. If you wanted to change the order of the directives to avoid warnings, the example would appear as follows:

1.	elephant : .bss : peanuts.o popcorn.o;
4.	monkey = LOAD V0x80000000 L0x4000;
2.	monkey : $PROGBITS ?AX;
3.	monkey : .bss;
6.	donkey = ?RX A0x1000;
5.	donkey : .bss;
7.	text = V0x80008000;

This order eliminates all warnings.