[dankoncs]

Okay, let me give another try for this:

So then we have 2 APIs. That is, we have the C standard library (as an API) and the POSIX API. The POSIX API defines the syscalls such as write, read, open, ... The C or C++ standard library provide the header files (function declarations etc.) and its .so file (the shared library) is in the memory. Take the Microsoft C++ Compiler as an example. I cannot see how the standard library is implemented, because only the headers are defined and the actual compiled code "lives" as a .so file in memory. This .so file as an object in memory is accessible to all C/C++ applications. The .so file is essentially C's runtime environment (RTE). (Also, C and C++ are standardized so no matter who implements the compiler and the standard library, it has to follow the language standard.)

The standard library among other things is not only providing a wrapper for syscalls such as malloc and printf (POSIX API), it is also providing some useful functions or algorithms such as qsort, std::transform... Furthermore, data structure or containers can also be part of a standard library: std::vector, std::unordered_map, ...

Now, if we compile a C or C++ program, the ABI is basically a set of definitions/rules, that the compiler has to abide to. Meaning things like how function parameters are stored (stacked or in registers), how a function should be called, how arguments are passed, how operations are mapped to machine code etc. But not only is an ABI a mapping or layout between C instructions and machine code, it is also a mapping between OS syscalls and C or C++ code.

Exception handling in C and POSIX is basically this:

#include <stdio.h>

#include <setjmp.h>

int main() {

  jmp_buf env;

  if (!setjmp(env)) /* try - something might go wrong in the subsequent code block (try block) better bookmark this line */

    longjmp(env, 1); /* throw an exception trigger the catch (else) block by going back to that bookmarked line */

  else /* catch */

    fprintf(stderr, "Yikes, something went wrong! ;)\n");

  return 0;

}

So if I do exception handling in C++, then the ABI of C++ should follow an exception handling routine. For example, virtual functions in C are basically this:

https://godbolt.org/z/x94cdb1Y5

So vtables are structs of function pointers. The C++ compiler has to follow some ABI convention (namely, some rule how to map or translate a vtable implementation such that it corresponds to the C++ code.)

- syscalls ~ POSIX API (operating systems API) ~ write, read, open, ...

- C/C++ standard library (.so files loaded in computer memory) ~ wrapper for syscalls (printf, malloc, ...), containers/data structures/algorithms (std::vector, std::unordered_map, qsort, ...)

-ABI ~ rules for the compiler that tell how vtables, function calls, exceptions should be implemented

Correct so far? Or am I still wrong?

[retrac]

Yes, you seem to have got it.