Public, Global, and Local Symbols

The symbol handling capabilities of the DbgHelp API have evolved over the years. To ensure that your code works in a variety of scenarios and provides full details on the symbols, use the newest functions whenever possible. For example, SymEnumSymbols replaces SymEnumerateSymbols64, SymFromName replaces SymGetSymFromName64, and SymFromAddr replaces SymGetSymFromAddr64.

Public Symbols

Initial versions of DbgHelp.dll supported examining only public symbols. These symbols are generated for any item in the code that must be exposed between different source files. They also include all items that are exported out of the module.

The symbols are either embedded in the image, or stored separately in a .dbg or .pdb file. The only information stored is the symbol name and address. The names are available as decorated names. To view undecorated names, call the SymSetOptions function with SYMOPT_UNDNAME, or use the UnDecorateSymbolName function.

Note that the DbgHelp API was not initially designed to support multiple instances of the same symbol within a module. This is because public symbols are restricted to unique names within a module. Therefore, SymGetSymFromName64 returns only the first symbol that matches. To retrieve all symbols that match, call SymEnumSymbols.

Global and Local Symbols

Newer versions of DbgHelp.dll support global and local symbols when using .pdb files. These new versions include static functions, functions scoped within a source file, function parameters, and local variables. When DbgHelp searches for a symbol, it checks the global and local symbol tables before checking the public symbol table. This is because there is more information available for these types of symbols than is available for public symbols.

Global and local symbols are stored with undecorated names. Therefore, the SYMOPT_UNDNAME flag has no effect. To get decorated symbol names, you must use the SYMOPT_PUBLICS_ONLY flag. This causes DbgHelp to search only the public symbols.

To view local symbols or function parameters, call the SymSetContext function with the InstructionOffset member of the IMAGEHLP_STACK_FRAME structure set to the address of any function symbol. Subsequent calls to SymFromName and SymEnumSymbols can operate within the context of this address. To do so, set the BaseOfDll parameter to NULL and omit the module specifier from the Name or Mask parameter. This forces DbgHelp to search for matching symbols within the scope indicated by SymSetContext.

To determine if a symbol is a parameter, check the Flags member of the SYMBOL_INFO structure. If the symbol is a parameter, the member contains SYMFLAG_PARAMETER. If it is a local symbol, the member contains SYMFLAG_LOCAL.

 

 

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