c library x86/x64 assembler

Question

Is there a C library for assembling a x86/x64 assembly string to opcodes?

Example code:

/* size_t assemble(char *string, int asm_flavor, char *out, size_t max_size); */

unsigned char bytes[32];
size_t size = assemble("xor eax, eax\n"
                       "inc eax\n"
                       "ret",
                       asm_x64, &bytes, 32);

for(int i = 0; i < size; i++) {
    printf("%02x ", bytes[i]);
}

/* Output: 31 C0 40 C3 */

I have looked at asmpure, however it needs modifications to run on non-windows machines.

I actually both need an assembler and a disassembler, is there a library which provides both?

Answer 1

There is a library that is seemingly a ghost; its existance is widely unknown:

XED (X86 Encoder Decoder)

Intel wrote it: https://software.intel.com/sites/landingpage/pintool/docs/71313/Xed/html/

It can be downloaded with Pin: https://software.intel.com/en-us/articles/pintool-downloads

Answer 2

Sure - you can use llvm. Strictly speaking, it's C++, but there are C interfaces. It will handle both the assembling and disassembling you're trying to do, too.