Obviously it was my conception of COMDATs that was flawed specifically that a variable explicitly tagged for the COMDAT section would be included with the mentioned /OPT:NOREF present.Īs somewhat of a digression (though not really): what makes an object of internal storage be kept, granted that it's type is referenced in the linking application? I've interpreted the documents in ways such that unreferenced data would be linked with /OPT:NOREF flag specified, and that their failure to do so were the result of a bug since /INCLUDE successfully overrode the discarding. I don't see how that supports your case.Īgain replacing operator new/delete wouldn't work as it works today with your suggested process.
That causes all non-COMDAT sections to be included. If the symbol is referenced, the object file is selected. I don't quite understand your /INCLUDE argument.
Construct 3 global variables code#
Also inlining and cross-module optimizations were certainly not nearly at a state where they are today. You rarely had code in a source file that was potentially not required.ĬOMDATs are a cheap solution for the special needs of C++, but obviously one would design a linkage system for C++ quite differently, if you didn't have the historic heritage. Obviously, the latter was designed for C/assembler only. Once an object file is selected, all of its symbols & references are added to the current state and the process continues.
it is how some of operator new/delete form overloads replacement works). That's why you can override some library functions in your own code (e.g. The linker initially starts with all object files given on the command line and then recursively selects object files from the static libraries until all symbol references are satifisied (or an error occurs).
Construct 3 global variables archive#
Basically, archive have a global archive table which maps symbols with global/weak binding to a particular object file member. The way object file selection from archives works is a bit different. The linker determines whether a particular COMDAT section is required based on symbol references (these are almost always relocations, even though COMDAT section grouping features exist in similar ways in both MS/COFF & ELF). inline functions, vtables of polymorphic classes without a decider function). The obvious uses are things with external linkage that do not violate the ODR (e.g. COMDAT sections allow for duplicating input sections in several contributing object files where only one is selected. Standard (non-COMDAT) input sections are merged when the corresponding object file is selected. In my definition and the one of at least four major toolchain implementators, it is not.Īgain unreferenced COMDAT elimination operates on sections - specifically on sections from object files (often called input sections in the ELF world and sometimes called section contributions in the MS/COFF world), many input sections of the same name contribute to a single output section. Your first argument (BTW: how do you do these quotes, I'm apparently too dumb to use the web interface) only holds if the corresponding translation unit is part of the program. For instance, the debugger can't materialize a breakpoint on a given code line if the containing translation unit was not built with debug information enabled. Of course, you should really be certain that the initializers are not called. The /VERBOSE linker switch will reveal why a particular object file is selected from a library or not. If the containing object file is selected the input section from that object file will contribute to the corresponding output section (It's not a COMDAT section). The CRT initialization invokes the initializers before entering the user supplied main function. Rather, the compiler injects pointers to generated initialization functions for objects with nontrivial constructors or destructors or those requiring dynamic initialization. These pointers are emitted into a special section - typically. While, an implementation may defer construction VC does not. The unreferenced COMDAT elimination phase runs logically after that (even though a smarter linker will probably construct the dependency graph earlier). Object files are selected from an archive, if and only if they are required to satisfy a strong symbol reference (via the archive symbol table). AFAICT, that's not a bug but it is the way all significant linkers work and have ever worked.
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