When an exception is thrown in C++ and caught by one of the calling functions, the supporting libraries need to unwind the stack. With gcc this is done using a variant of DWARF debugging information. The unwind information is loaded at runtime, but is not read unless an exception is thrown. That means that the […]
If you followed my last post, you will see that in order to unwind the stack you have to find the FDE associated with a given program counter value. There are two steps to this problem. The first one is finding the CIEs and FDEs at all. The second one is, given the set of […]
C++ Template Instantiation There is still more C++ fun at link time, though somewhat less related to the linker proper. A C++ program can declare templates, and instantiate them with specific types. Ideally those specific instantiations will only appear once in a program, not once per source file which instantiates the templates. There are a […]
ELF Segments Earlier I said that executable file formats were normally the same as object file formats. That is true for ELF, but with a twist. In ELF, object files are composed of sections: all the data in the file is accessed via the section table. Executables and shared libraries normally contain a section table, […]
Throwing an exception in C++ requires more than unwinding the stack. As the program unwinds, local variable destructors must be executed. Catch clauses must be examined to see if they should catch the exception. Exception specifications must be checked to see if the exception should be redirected to the unexpected handler. Similar issues arise in […]