Undefined symbol in lumen ohm code#

If, during execution of the application, the function address tests nonzero, the function is called. When an application is built that references libfoo.so.1, the link-edit will complete successfully regardless of whether a definition for the symbol foo isįound.

Undefined symbol in lumen ohm code#

For example, the following C code fragment might have been used Historically, these undefined weak referenced symbols have been employed as a mechanism to test for the existence of functionality. During process execution, the runtime linker searches for this symbol, and if itĭoes not find a match, binds the reference to an address of zero instead of generating a fatal runtime relocation error. If a dynamic executable or shared object is being produced, the symbol will be left as an undefined weak reference. If a static executable is being generated, the symbol is converted to an absolute symbol and assigned a value of zero.

Weak symbol references that are not bound during a link-edit do not result in a fatal error condition, no matter what output file type is being generated. In this case the shared object can be employedīy many users, without those users having to determine and establish dependencies to satisfy the shared objects requirements. In general, a self-contained shared object, in which all references to external symbols are satisfied by named dependencies, provides maximum flexibility. The extern mapfile directive described in 'Defining Additional Symbols'). The link-editor's -z defs option can be used to force a fatal error if any undefined symbols remain (see also Objects or other shared objects when it is used to build a dynamic executable. This allows the shared object to import symbols from either relocatable When the link-editor is generating a shared object, it will by default allow undefined symbols to remain at the end of the link-edit.

Required reference is hinted at in the fatal error message shown in this example). Thus, prog will fail to run if a new version of libbar.so is developed that no longer has a dependency on libfoo.so.įor this reason, bindings of this type are deemed fatal, and the implicit reference must be made explicit by referencing the library directly during the link-edit of prog (the However, only explicit shared object dependencies are recorded in the output file being generated.

Here prog is being built with an explicit reference to libbar.so, and because libbar.so has a dependency on libfoo.so, an implicit reference to libfoo.so from prog is established.īecause main.c made a specific reference to the interface provided by libfoo.so, then prog really has a dependency on libfoo.so. With the files main.c and foo.c used in the previous example: Symbols can also remain undefined when a symbol reference in a relocatable object is bound to a symbol definition in an implicitly defined shared object. Although thisĮrror can be detected during the initial execution and testing of an application, more complex execution paths can result in this error condition taking much longer to detect, which can be time consuming If an unavailable symbol reference is required during the execution of a process, a fatal runtime relocation error will occur. Take care when using the -z nodefs option. If you want to allow undefined symbols, as in cases like the previous example, then the default fatal error condition can be suppressed by using the link-editor's -z nodefs option.

In a similar manner, a symbol reference within a shared object that is never matched to a symbol definition when the shared object is being used to build a dynamic executable, will also result in When the link-editor is generating an executable output file, the link-editor's default behavior is to terminate the link-edit with an appropriate error message should any symbols remain undefined.Ī symbol remains undefined when a symbol reference in a relocatable object is never matched to a symbol definition: The effect of these undefined symbols on the link-edit process can vary according to the type of output file being generated,Īnd possibly the type of symbol. These symbol references are referred to as undefined symbols. After all input files have been read and all symbol resolution is complete, the link-editor searches the internal symbol table for any symbol references that have not been bound to symbol definitions.