This variable attribute affects the visibility of ELF symbols.
This attribute is a GNU compiler extension supported by the ARM compiler.
one of the following:
The assumed visibility of symbols can be changed by other options. Default visibility overrides such changes. Default visibility corresponds to external linkage.
The symbol is not placed into the dynamic symbol table, so no other executable or shared library can directly reference it. Indirect references are possible using function pointers.
Unless otherwise specified by the processor-specific Application Binary Interface (psABI), internal visibility means that the function is never called from another module.
The symbol is placed into the dynamic symbol table, but references within the defining module bind to the local symbol. That is, the symbol cannot be overridden by another module.
Except when specifying
this attribute is intended for use with declarations that would
otherwise have external linkage.
You can apply this attribute to functions and variables in C and C++. In C++, you can also apply it to class, struct, union, and enum types, and namespace declarations.