Mapfile Directives for Predefined Segments and Entrance Criteria

The link-editor provides a predefined set of output segment descriptors and entrance criteria, as described in Predefined Segments. The link-editor already knows about these sections, so mapfile directives are not required to create them. The mapfile directives that could be used to produce them are shown for illustrative purposes, and as an example of a relatively complex mapfile specification. Mapfile segment directives can be used to modify or augment these built in definitions.

Normally, section to segment assignments are done within a single segment directive. However, the predefined sections have more complex requirements, requiring their entrance criteria to be processed in a different order than the segments are laid out in memory. Two passes are used to achieve this, the first to define all the segments in the desired order, and the second to establish entrance criteria in an order that will achieve the desired results. It is rare for a user mapfile to require this strategy.

        # Predefined segments and entrance criteria for the Oracle Solaris
        # link-editor
        $mapfile_version 2

        # The lrodata and ldata segments only apply to x86-64 objects.
        # Establish amd64 as a convenient token for conditional input
        $if _ELF64 && _x86
        $add amd64
        $endif

        # Pass 1: Define the segments and their attributes, but
        # defer the entrance criteria details to the 2nd pass.
        LOAD_SEGMENT text {
                FLAGS = READ EXECUTE;
        };
        LOAD_SEGMENT data {
                FLAGS = READ WRITE EXECUTE;
        };
        LOAD_SEGMENT bss {
                DISABLE;
                FLAGS=DATA;
        };
        $if amd64
                LOAD_SEGMENT lrodata {
                        FLAGS = READ
                };
                LOAD_SEGMENT ldata {
                        FLAGS = READ WRITE;
                };
        $endif
        NOTE_SEGMENT note;
        NULL_SEGMENT extra;

        # Pass 2: Define ASSIGN_SECTION attributes for the segments defined
	       # above, in the order the link-editor should evaluate them.

        # All SHT_NOTE sections go to the note segment
        NOTE_SEGMENT note {
                ASSIGN_SECTION {
                        TYPE = NOTE;
                };
        };
        $if amd64
                # Medium/large model x86-64 readonly sections to lrodata
                LOAD_SEGMENT lrodata {
                        ASSIGN_SECTION {
                                FLAGS = ALLOC AMD64_LARGE;
                        };
                };
        $endif

        # text receives all readonly allocable sections
        LOAD_SEGMENT text {
                ASSIGN_SECTION {
                        FLAGS = ALLOC !WRITE;
                };
        };

        # If bss is enabled, it takes the writable NOBITS sections
        # that would otherwise end up in ldata or data.
        LOAD_SEGMENT bss {
                DISABLE;
                ASSIGN_SECTION {
                        FLAGS = ALLOC WRITE;
                        TYPE = NOBITS;
                };
        };

        $if amd64
                # Medium/large model x86-64 writable sections to ldata
                LOAD_SEGMENT ldata {
                        ASSIGN_SECTION {
                                FLAGS = ALLOC WRITE AMD64_LARGE;
                        };
                        ASSIGN_SECTION {
                                TYPE = NOBITS;
                                FLAGS = AMD64_LARGE
                        };
                };
        $endif

        # Any writable allocable sections not taken above go to data
        LOAD_SEGMENT data {
                ASSIGN_SECTION {
                        FLAGS = ALLOC WRITE;
                };
        };

        # Any section that makes it to this point ends up at the
        # end of the object file in the extra segment. This accounts
        # for the bulk of non-allocable sections.
        NULL_SEGMENT extra {
                ASSIGN_SECTION;
        };