This warning is generated by CODAN (Code Analysis function); a part of the eclipse standard C development plugin CDT.
Solutions are described for each cases.
[Case1: Warned for compiler's internal symbol or keyword]
This issue may be caused by compiler specific symbols (so called "keyword", e.g. __far) because CODAN can't recognize symbols which are not defined on any header files.
In such cases, adding any of the following declarations would solve this issue. Please consult the compiler manuals for the specific symbols.
code example for RX Family C/C++ Compiler Package (CC-RX)
code example for RL78 Family C Compiler Package (CC-RL)
[Case2: Symbols are undefined, or lacking for header file path settings]
CODAN tries to solve symbols in header files based on "include path" setting.
The error in this title occurs if symbols were not found.
Please visit "C/C++ General" -> "Paths and Symbols" of project property and check "include
directories" file paths.