SPRUI03E June 2015 – January 2023
Identify a Symbol to be Treated as a Weak Symbol
.weak symbol name
The .weak directive identifies a symbol that is used in the current module but is defined in another module. The linker resolves this symbol's definition at link time. Instead of including a weak symbol in the output file's symbol table by default (as it would for a global symbol), the linker only includes a weak symbol in the output of a "final" link if the symbol is required to resolve an otherwise unresolved reference. See Section 3.7.3 for details about how weak symbols are handled by the linker.
The .weak directive is equivalent to the .ref directive, except that the reference has weak linkage.
The .weak directive always creates a symbol table entry for a symbol, whether the module uses the symbol or not. The .symdepend directive, in contrast, creates an symbol table entry only if the module actually uses the symbol (see .symdepend topic).
If a symbol is not defined in the current module (which includes macro, copy, and include files), use the .weak directive to tell the assembler that the symbol is defined in an external module. This prevents the assembler from issuing an unresolved reference error. At link time, the linker looks for the symbol's definition in other modules.
For example, use the .weak and .set directives in combination as shown in the following example, which defines a weak absolute symbol "ext_addr_sym":
.weak ext_addr_sym
ext_addr_sym .set 0x12345678If you assemble such assembly source and include the resulting object file in the link, the "ext_addr_sym" in this example is available as a weak absolute symbol in a final link. It is a candidate for removal if the symbol is not referenced elsewhere in the application.