Itanium ABI
- C++ course
- Expert
- Lesson 21/47
- 5 min
Learn the Itanium ABI and its common usage.
Itanium ABI
The Itanium C++ ABI is the mangling and layout standard shared by GCC and Clang. It was first designed for the Itanium architecture but became the default ABI on all architectures on Linux and macOS.
The Itanium mangling rules are documented; this lets different compilers produce the same symbol names. Example: void foo() → _Z3foov. MSVC uses its own ABI; that is why a GCC-compiled library cannot link directly to an MSVC program. C linkage (extern "C") is the common bridge.
Type codes
The Itanium ABI type codes are single letters: v = void, i = int, d = double, b = bool, c = char, l = long. Names are written with a length prefix: 5print = print.
So the signature void print(int) becomes _Z5printi: _Z prefix, 5print name, i int parameter. As long as the signature does not change, the symbol stays the same; this is the basis of ABI stability.
Practice Write a namespaced function
Write namespace ns { int compute(int x) { return x * 2; } }. In main write std::cout << ns::compute(5);.
Starter code
#include <iostream>
// Define the compute function in namespace ns here
int main() {
// Call compute and print it
return 0;
}Sample solution
#include <iostream>
namespace ns {
int compute(int x) {
return x * 2;
}
}
int main() {
std::cout << ns::compute(5);
return 0;
}Expected output
10
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match each symbol to its signature
| Term | Meaning |
|---|---|
_Z3foov |
foo() symbol |
_Z3addii |
add(int, int) symbol |
_ZN2ns3barEv |
ns::bar() symbol |
_Z3bazv |
baz() symbol |
2 Complete the mangled name
_Z3foo____ // void foo()_Z3foov // void foo()Explanation: The v type code means void.
3 What does the 'i' type code represent in the Itanium ABI?
_Z3addii // add(int, int)- int Correct answer
- double
- bool
- void
Explanation: The right answer is: int. In Itanium, i = int, d = double, v = void, b = bool.