How to call a C compiler through library instead of via system call?

Question

In a project that I have been asked to revise, there is a segment of code that is tantamount to just generating a set of assembly instructions, writing them to a file, and then compiling it with the gcc compiler.

My question is, is there any way to link in a library that would do this work for me via an exposed API call? I need 1-1 equivalence to the following command:

gcc -m32 -c -o objfile generated_asm.asm -masm=intel

possible duplicate of [c library x86/x64 assembler](http://stackoverflow.com/questions/17001094/c-library-x86-x64-assembler) — unwind, Oct 28 '14 at 14:57
Succinctly, no. The compiler is not an API that's callable from a program; it is a (rather large) program in its own right. Using `system()` is the sane way to do the job. — Jonathan Leffler, Oct 28 '14 at 14:57
I'm not actually loading and running the compiled code, this is for binary level analysis. — Adam Miller, Oct 28 '14 at 15:09
It's faster and avoids the passing around of file names... idk, it seems proper (?) — Adam Miller, Oct 28 '14 at 19:00
Unless you can demonstrate, quantitatively, that running a separate process for this task makes your program noticeably slower than required, speed is a non-issue. — n. m. could be an AI, Oct 31 '14 at 21:12
@AdamMiller It's only faster if it exists. If it doesn't exist, it isn't faster. You're perpetrating a logical fallacy. — user207421, Dec 02 '14 at 09:35

score 2 · Accepted Answer · edited May 23 '17 at 12:04

You cannot do exactly that. You might fork the GCC compilation command. It is probably operating system specific, I'm supposing you are on Linux (or some other POSIX system).

However, there are alternatives:

using asmjit to generate x86 machine code in memory
using tinycc and its libtcc library (which can compile a string containing C or asm code; beware, the compiled machine code is slow since unoptimized)
using a JIT library like libjit, or LLVM, or GNU lightning
coding in a metaprogramming language like Common Lisp (e.g. SBCL) or MetaOcaml

Also, you could simply fork a GCC compilation of some generated C file genfoo.c into a shared object (gcc -Wall -O -fPIC genfoo.c -shared -o genfoo.so) then dynamically loading with dlopen the ./genfoo.so file (see also this)

PS. Next GCC 5.0 release will have a JIT library (libgccjit).

Ira Baxter · Answer 2 · 2014-12-02T11:04:56.377

2

Generally, no, because Unix insisted we think of everything as text strings (including command lines). And we all accepted Unix.

Technically GCC is just giant subroutine with a big parameter list.

The fact that you get to it though a text string is a stupid design decision we all made by dumping Multics and/or LISP machines. On these systems, subroutines (even big ones) are all called natively, and thus really compose.

With Multics, the compiler is (well was, Multics is pretty dead) a subroutine you can call. (Yes, there was a command line interface that could also make that call, so people could invoke it).

edited Dec 02 '14 at 11:04

answered Dec 02 '14 at 10:29

Ira Baxter

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I disagree with the "GCC is just giant subroutine with a big parameter list" phrase. There is no common data (or closed values) between GCC and the invoking process (since they are separate processes with separate address spaces) – Basile Starynkevitch Dec 02 '14 at 12:07
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Just goes to show what a clumsy parameter passing process Unix commands have. – Ira Baxter Dec 02 '14 at 16:53

How to call a C compiler through library instead of via system call?

2 Answers2