[Main] Title=Conditional Reaction to Global Imports Index=..._AND_..., NOT_... [Top] Sometimes, it is convenient for an archive member to react to a global import differently than just to be included whenever the import is created. For example, a startup section may be optimized better if a certain register already holds a certain value, otherwise it must compute the value by itself. The TIGCC linker defines two symbol operators for this purpose: To be included only if the global imports A and B are defined, a file must export the symbol A_AND_B. To be included only if the global import A is not defined, a file must export the symbol NOT_A. Symbol operators may be combined, i.e. a file exporting NOT_A_AND_B is included only if no global import A exists, and a global import B is defined.

There is a small quirk related to negated conditions: At some point, the linker needs to assume that no global imports A and B exist, and any file exporting the symbol NOT_A or NOT_B needs to be imported. However, the file which exported NOT_B may actually create a global import A after the file exporting NOT_A has been imported. The linker does not detect this, so you need to be careful not to create such situations. They are especially difficult to detect if a lot of combinations of AND and NOT operators are used, and if a lot of files that react to global imports create imports of their own.