DSECT, COPY, NOLOAD, INFO, and OVERLAY sections

Sections in a COFF file may be given a type in a section definition, as shown in the following example:

   SECTIONS
   {
           name1 0x200000 (DSECT)       : { file1.o }
           name2 0x400000 (COPY)        : { file2.o }
           name3 0x600000 (NOLOAD)      : { file3.o }
           name4          (INFO)        : { file4.o }
           name5 0x900000 (OVERLAY)     : { file5.o }
   }

The DSECT option creates a dummy section. A dummy section has the following properties:

• It does not participate in the memory allocation for output sections. As a result, it takes up no memory and does not show up in the memory map generated by ld.

• It may overlay other output sections and even unconfigured memory. DSECTs may overlay other DSECTs.

• The global symbols defined within the dummy section are relocated normally. That is, they appear in the output file's symbol table with the same value they would have had if the DSECT were actually loaded at its virtual address. Symbols defined in a DSECT may be referenced by other input sections. Undefined external symbols found within a DSECT cause specified archive libraries to be searched: any members which define such symbols are link edited normally.

• None of the section contents, relocation information, or line number information associated with the section is written to the output file.

In the above example, none of the sections from file1.o are allocated, but all symbols are relocated as though the sections were link edited at the specified address. Other sections could refer to any of the global symbols and they are resolved correctly.

A copy section created by the COPY option is similar to a dummy section. The difference between a COPY section and a dummy section is that the contents of a COPY section and all associated information is written to the output file.

An INFO section is similar to a COPY section: instead of containing valid text and data, as a COPY section does, its purpose is to carry information about the object file. INFO sections are usually used to contain file version identification information.

A section with type NOLOAD differs in only one respect from a normal output section: its text or data is not written to the output file. A NOLOAD section is allocated virtual space, appears in the memory map, and so on.

An OVERLAY section is relocated and written to the output file. It is different from a normal section in that it is not allocated and may overlay other sections or unconfigured memory.