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 = .DYSYMTAB,
LC_DYSYMTAB
cmdsize: u32 = @sizeOf(dysymtab_command),
sizeof(struct dysymtab_command)
ilocalsym: u32 = 0,
index of local symbols
nlocalsym: u32 = 0,
number of local symbols
iextdefsym: u32 = 0,
index to externally defined symbols
nextdefsym: u32 = 0,
number of externally defined symbols
iundefsym: u32 = 0,
index to undefined symbols
nundefsym: u32 = 0,
number of undefined symbols
tocoff: u32 = 0,
file offset to table of contents
ntoc: u32 = 0,
number of entries in table of contents
modtaboff: u32 = 0,
file offset to module table
nmodtab: u32 = 0,
number of module table entries
extrefsymoff: u32 = 0,
offset to referenced symbol table
nextrefsyms: u32 = 0,
number of referenced symbol table entries
indirectsymoff: u32 = 0,
file offset to the indirect symbol table
nindirectsyms: u32 = 0,
number of indirect symbol table entries
extreloff: u32 = 0,
offset to external relocation entries
nextrel: u32 = 0,
number of external relocation entries
locreloff: u32 = 0,
offset to local relocation entries
nlocrel: u32 = 0,
number of local relocation entries