Difference between API and ABI

Question

I am new to linux system programming and I came across API and ABI while reading Linux System Programming.

Definition of API :

Answer 1

Your program (source code) can be compiled with modules who provide proper API.

Your program (binary) can run on platforms who provide proper ABI.

API restricts type definitions, function definitions, macros, sometimes global variables a library should expose.

ABI restricts what a "platform" should provide for you program to run on. I like to consider it in 3 levels:

• processor level - the instruction set, the calling convention

• kernel level - the system call convention, the special file path convention (e.g. the /proc and /sys files in Linux), etc.

• OS level - the object format, the runtime libraries, etc.

Consider a cross-compiler named arm-linux-gnueabi-gcc. "arm" indicates the processor architecture, "linux" indicates the kernel, "gnu" indicates its target programs use GNU's libc as runtime library, different from arm-linux-androideabi-gcc which use Android's libc implementation.