Why Does My C Program Need `__gxx_personality_v0`?

Understanding the Purpose of __gxx_personality_v0

A popular question on OS development forums has sparked inquiry into the enigmatic __gxx_personality_v0 symbol. When compiling and linking free-standing C programs using gcc, users often encounter a linker error involving this undefined reference.

The Significance in Stack Unwinding

Delving into the assembly output of related questions reveals the true nature of __gxx_personality_v0. It plays a crucial role in stack unwinding tables, as defined by the Itanium C ABI. Often referred to as the Personality Routine, its function is to establish the behavior of a program's stack unwinding upon exceptions.

Linking with g for Exception Support

Despite its name, gcc alone is not equipped to handle exception handling. To incorporate this functionality into your program, you must link with g , which will automatically include -lstdc . By doing so, you gain access to the required library containing the __gxx_personality_v0 symbol. This enables your program to properly unwind its stack when exceptions occur.

Disabling Exceptions for Free-Standing Programs

If your program does not utilize exceptions, you can safely disable them with the -fno-exceptions compiler flag. This will eliminate the need for the __gxx_personality_v0 symbol. Similarly, you can disable RTTI (runtime type information) using -fno-rtti if your program does not require it.

Void Pointer Substitution for Basic Functionality

In certain free-standing environments where exceptions are not enabled, the simple definition of __gxx_personality_v0 as a global NULL void pointer may suffice. This method will prevent the linker error but does not fully replicate the functionality of a valid Personality Routine. Without exception handling, the program will likely encounter errors if it attempts to throw exceptions.

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