Re: A technique to mock "static interfaces" (e.g. isInputRange)

[Jacob Carlborg via Digitalmars-d]

On 2016-05-27 15:12, Atila Neves wrote:

I get an SSL warning for that link.

Hmm, here's the code inline:

module red;

import std.stdio;

import core.sys.posix.sys.mman : mprotect, PROT_NONE, PROT_READ, 
PROT_WRITE, PROT_EXEC;
import core.stdc.errno : errno;
import core.stdc.string : memmove, memcpy;

extern (C) int getpagesize();

void procWrite(void* pos, const ref ubyte[6] data)
{
    void* addr = pos;
    size_t page = getpagesize();
    addr -= (cast(size_t)addr) % page;

    if(0 != mprotect(addr, page, PROT_READ | PROT_WRITE | PROT_EXEC)){
        return; // error
    }
    memmove(pos, data.ptr, data.length);
    mprotect(pos, page, PROT_READ | PROT_EXEC);
}

ubyte[6] redirect(void* from, void* to)
{

    // compute ASM
    ubyte[6] cmd;

    // // sanity checks
    if(((from <= to) && (to <= from+5))
        || ((to <= from) && (from <= to+5)))
    {
        return cmd;
        //throw new Exception("illegal source-destination combination");
    }

    cmd[0] = 0xE9; // jmp
    cmd[5] = 0xC3; // retn

    size_t new_dest = cast(size_t) to;
    new_dest = new_dest - (cast(size_t)from + 5);
    int offset = cast(int)cast(ptrdiff_t)new_dest;

    cmd[1 .. 1 + offset.sizeof] = (cast(ubyte*)&offset)[0 .. 
offset.sizeof];

    // // save original
    ubyte[6] original = (cast(ubyte*)from)[0 .. cmd.length];

    // write asm
    procWrite(from, cmd);
    return original;
    // return null;
}

void restoreRedirection(void* addr, const ref ubyte[6] data)
{
    procWrite(addr, data);
}

void a()
{
    writeln("a");
}

void b()
{
    writeln("b");
}

void bar(Foo foo)
{
    writeln("bar");
}

class Foo
{
    void foo()
    {
        writeln("foo");
    }
}

void replaceMethod()
{
    auto f = new Foo;
    auto f2 = new Foo;
    auto vtbl = (cast(void**)f.__vptr)[0 .. 6].dup;
    vtbl[5] = &bar;
    f.__vptr = cast(immutable(void*)*) vtbl.ptr;
    f.foo();
    f2.foo();
}

void replaceFunction()
{
    a();
    auto r = redirect(&a, &b);
    a();
    restoreRedirection(&a, r);
    a();
}

void main()
{
    replaceMethod();
    replaceFunction();
}

--
/Jacob Carlborg