ASSIGN_SECTION Attribute

ASSIGN_SECTION specifies a combination of section attributes, such as section name, type, and flags, that collectively qualify a section for assignment to a given segment. Each such set of attributes is called an entrance criterion. A section matches when the section attributes match those of an entrance criterion exactly. An ASSIGN_SECTION that does not specify any attributes matches any section that criterion is compared to.

Multiple ASSIGN_SECTION attributes are allowed for a given segment. Each ASSIGN_SECTION attribute is independent of the others. A section will be assigned to a segment if the section matches any one of the ASSIGN_SECTION definitions associated with that segment. The link-editor will not assign sections to a segment unless the segment has at least one ASSIGN_SECTION attribute.

The link-editor uses an internal list of entrance criteria to assign sections to segments. Each ASSIGN_SECTION declaration encountered in the mapfile is placed on this list, in the order encountered. The entrance criteria for the built-in segments discussed in Predefined Segments are placed on this list immediately following the final mapfile defined entry.

The entrance criterion can be given an optional name (assign_name). This name can be used in conjunction with the IS_ORDER attribute to specify the order in which input sections are placed in the output section.

To place an input section, the link-editor starts at the head of the entrance criteria list, and compares the attributes of the section to each entrance criterion in turn. The section is assigned to the segment associated with the first entrance criterion that matches the section attributes exactly. If there is no match, the section is placed at the end of the file, as is generally the case for all non-allocable sections.

ASSIGN_SECTION accepts the following.

• FILE_BASENAME, FILE_OBJNAME, FILE_PATH

  These attributes allow the selection of sections based on the path (FILE_PATH), basename (FILE_BASENAME), or object name (FILE_OBJNAME) of the file they come from.

  File paths are specified using the standard Unix slash delimited convention. The final path segment is the basename of the path, also known simply as the filename. In the case of an archive, the basename can be augmented with the name of the archive member, using the form archive_name(component_name). For example, /lib/libfoo.a(bar.o)specifies the object bar.o, found in an archive named /lib/libfoo.a.

  FILE_BASENAME and FILE_OBJNAME are equivalent when applied to a non-archive, and compare the given name to the basename of the file. When applied to an archive, FILE_BASENAME examines the basename of the archive name, while FILE_OBJNAME examines the name of the object contained within the archive.

  Each ASSIGN_SECTION maintains a list of all FILE_BASENAME, FILE_PATH, and FILE_OBJNAME values. A file match occurs if any one of these definitions match an input file.

• IS_NAME

  Input section name.

• TYPE

  Specifies an ELF section_type, which can be any of the SHT_ constants defined in <sys/elf.h>, with the SHT_ prefix removed. (e.g. PROGBITS, SYMTAB, NOBITS).

• FLAGS

  The FLAGS attribute uses section_flags to specify section attributes as a space separated list of one or more of the values given in Table 9–7, which correspond to the SHF_ values defined in <sys/elf.h>. If an individual flag is preceded by an exclamation mark (!), that attribute must explicitly not be present. In the following example, a section is defined allocable and not writable.

          ALLOC !WRITE

  Flags not explicitly in a section_flags list are ignored. In the above example, only the value of ALLOC and WRITE are examined when matching a section against the specified flags. The other section flags can have any value.