dankoncs

This would be my (possibly wrong) explanation:

So in Linux we have syscalls such as write, read, close, socket, ... These syscalls are defined according to the POSIX standard. POSIX is basically a standard for operating systems. Linux/Unix follow these standards. So syscalls are an interface so that we can communicate with the OS. (Is it the application binary interface already?)

Now, we have the C standard library, so we don't need to deal with syscalls (or specific OS stuff). The C standard library is basically an application programming interface (API). So printf, fopen etc. map to write, open, etc. respectively:

printf ~ write

fopen ~ open

fclose ~ close

...

Then, apparently, we require a runtime environment (RTE). This runtime environment (is perhaps) the standard library that is a .so file (a shared object). Shared objects are (perhaps) loaded by the OS to a specific memory location so that all C programs can access that .so file (which is now loaded in memory for all C executables to use.) So that .so file is the "RTE" and the syscalls are the "ABI"?

If so, I find "ABI" and "RTE" confusing. Java has an RTE. You need the Java Virtual Machine (an abstract CPU essentially) to run your .class files within that virtual machine (JVM).

Again, I am unsure about this, so please go easy on me. Thank you!

PS: Why do people like Jason Turner say: "break the ABI to save C++"? So break the .so files for C++'s standard library? What for? (Shouldn't it be: "break C++'s RTE"?)