extern struct dysymtab_command [src]

This is the second set of the symbolic information which is used to support the data structures for the dynamically link editor. The original set of symbolic information in the symtab_command which contains the symbol and string tables must also be present when this load command is present. When this load command is present the symbol table is organized into three groups of symbols: local symbols (static and debugging symbols) - grouped by module defined external symbols - grouped by module (sorted by name if not lib) undefined external symbols (sorted by name if MH_BINDATLOAD is not set, and in order the were seen by the static linker if MH_BINDATLOAD is set) In this load command there are offsets and counts to each of the three groups of symbols. This load command contains a the offsets and sizes of the following new symbolic information tables: table of contents module table reference symbol table indirect symbol table The first three tables above (the table of contents, module table and reference symbol table) are only present if the file is a dynamically linked shared library. For executable and object modules, which are files containing only one module, the information that would be in these three tables is determined as follows: table of contents - the defined external symbols are sorted by name module table - the file contains only one module so everything in the file is part of the module. reference symbol table - is the defined and undefined external symbols For dynamically linked shared library files this load command also contains offsets and sizes to the pool of relocation entries for all sections separated into two groups: external relocation entries local relocation entries For executable and object modules the relocation entries continue to hang off the section structures.

Fields

cmd: LC = .DYSYMTABLC_DYSYMTAB

cmdsize: u32 = @sizeOf(dysymtab_command)sizeof(struct dysymtab_command)

ilocalsym: u32 = 0index of local symbols

nlocalsym: u32 = 0number of local symbols

iextdefsym: u32 = 0index to externally defined symbols

nextdefsym: u32 = 0number of externally defined symbols

iundefsym: u32 = 0index to undefined symbols

nundefsym: u32 = 0number of undefined symbols

tocoff: u32 = 0file offset to table of contents

ntoc: u32 = 0number of entries in table of contents

modtaboff: u32 = 0file offset to module table

nmodtab: u32 = 0number of module table entries

extrefsymoff: u32 = 0offset to referenced symbol table

nextrefsyms: u32 = 0number of referenced symbol table entries

indirectsymoff: u32 = 0file offset to the indirect symbol table

nindirectsyms: u32 = 0number of indirect symbol table entries

extreloff: u32 = 0offset to external relocation entries

nextrel: u32 = 0number of external relocation entries

locreloff: u32 = 0offset to local relocation entries

nlocrel: u32 = 0number of local relocation entries

Source

  pub const dysymtab_command = extern struct {
    /// LC_DYSYMTAB
    cmd: LC = .DYSYMTAB,

    /// sizeof(struct dysymtab_command)
    cmdsize: u32 = @sizeOf(dysymtab_command),

    // The symbols indicated by symoff and nsyms of the LC_SYMTAB load command
    // are grouped into the following three groups:
    //    local symbols (further grouped by the module they are from)
    //    defined external symbols (further grouped by the module they are from)
    //    undefined symbols
    //
    // The local symbols are used only for debugging.  The dynamic binding
    // process may have to use them to indicate to the debugger the local
    // symbols for a module that is being bound.
    //
    // The last two groups are used by the dynamic binding process to do the
    // binding (indirectly through the module table and the reference symbol
    // table when this is a dynamically linked shared library file).

    /// index of local symbols
    ilocalsym: u32 = 0,

    /// number of local symbols
    nlocalsym: u32 = 0,

    /// index to externally defined symbols
    iextdefsym: u32 = 0,

    /// number of externally defined symbols
    nextdefsym: u32 = 0,

    /// index to undefined symbols
    iundefsym: u32 = 0,

    /// number of undefined symbols
    nundefsym: u32 = 0,

    // For the for the dynamic binding process to find which module a symbol
    // is defined in the table of contents is used (analogous to the ranlib
    // structure in an archive) which maps defined external symbols to modules
    // they are defined in.  This exists only in a dynamically linked shared
    // library file.  For executable and object modules the defined external
    // symbols are sorted by name and is use as the table of contents.

    /// file offset to table of contents
    tocoff: u32 = 0,

    /// number of entries in table of contents
    ntoc: u32 = 0,

    // To support dynamic binding of "modules" (whole object files) the symbol
    // table must reflect the modules that the file was created from.  This is
    // done by having a module table that has indexes and counts into the merged
    // tables for each module.  The module structure that these two entries
    // refer to is described below.  This exists only in a dynamically linked
    // shared library file.  For executable and object modules the file only
    // contains one module so everything in the file belongs to the module.

    /// file offset to module table
    modtaboff: u32 = 0,

    /// number of module table entries
    nmodtab: u32 = 0,

    // To support dynamic module binding the module structure for each module
    // indicates the external references (defined and undefined) each module
    // makes.  For each module there is an offset and a count into the
    // reference symbol table for the symbols that the module references.
    // This exists only in a dynamically linked shared library file.  For
    // executable and object modules the defined external symbols and the
    // undefined external symbols indicates the external references.

    /// offset to referenced symbol table
    extrefsymoff: u32 = 0,

    /// number of referenced symbol table entries
    nextrefsyms: u32 = 0,

    // The sections that contain "symbol pointers" and "routine stubs" have
    // indexes and (implied counts based on the size of the section and fixed
    // size of the entry) into the "indirect symbol" table for each pointer
    // and stub.  For every section of these two types the index into the
    // indirect symbol table is stored in the section header in the field
    // reserved1.  An indirect symbol table entry is simply a 32bit index into
    // the symbol table to the symbol that the pointer or stub is referring to.
    // The indirect symbol table is ordered to match the entries in the section.

    /// file offset to the indirect symbol table
    indirectsymoff: u32 = 0,

    /// number of indirect symbol table entries
    nindirectsyms: u32 = 0,

    // To support relocating an individual module in a library file quickly the
    // external relocation entries for each module in the library need to be
    // accessed efficiently.  Since the relocation entries can't be accessed
    // through the section headers for a library file they are separated into
    // groups of local and external entries further grouped by module.  In this
    // case the presents of this load command who's extreloff, nextrel,
    // locreloff and nlocrel fields are non-zero indicates that the relocation
    // entries of non-merged sections are not referenced through the section
    // structures (and the reloff and nreloc fields in the section headers are
    // set to zero).
    //
    // Since the relocation entries are not accessed through the section headers
    // this requires the r_address field to be something other than a section
    // offset to identify the item to be relocated.  In this case r_address is
    // set to the offset from the vmaddr of the first LC_SEGMENT command.
    // For MH_SPLIT_SEGS images r_address is set to the the offset from the
    // vmaddr of the first read-write LC_SEGMENT command.
    //
    // The relocation entries are grouped by module and the module table
    // entries have indexes and counts into them for the group of external
    // relocation entries for that the module.
    //
    // For sections that are merged across modules there must not be any
    // remaining external relocation entries for them (for merged sections
    // remaining relocation entries must be local).

    /// offset to external relocation entries
    extreloff: u32 = 0,

    /// number of external relocation entries
    nextrel: u32 = 0,

    // All the local relocation entries are grouped together (they are not
    // grouped by their module since they are only used if the object is moved
    // from its statically link edited address).

    /// offset to local relocation entries
    locreloff: u32 = 0,

    /// number of local relocation entries
    nlocrel: u32 = 0,
}  