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How to get the body of a function/asm statement in hexadecimal
January 29
Gravatar of Ruby the RoobsterPosted by Ruby the RoobsterReply
Ruby the Roobster
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I'm trying to do something like

void main()
{
    auto d = &c;
    *d.writeln;
}

void c()
{
}

In an attempt to get the hexadecimal representation of the machine code of a function. Of course, function pointers cannot be dereferenced. What do?

Furthermore, I would like to be able to do the same for an asm statement.

January 29
Gravatar of Ali ÇehreliPosted by Ali Çehreli
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Ali Çehreli
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On 1/29/23 13:45, Ruby the Roobster wrote:

> Of course, function pointers cannot be dereferenced.

Since you want to see the bytes, just cast it to ubyte*. The following function dumps its own bytes:

import std;

void main() {
    enum end = 0xc3;
    for (auto p = cast(ubyte*)&_Dmain; true; ++p) {
        writefln!" %02x"(*p);
        if (*p == end) {
            break;
        }
    }
}

(It can be written more elegantly as a range expression.)

> Furthermore, I would like to be able to do the same for an `asm` statement.

I don't know how to get the address of asm blocks.

Ali
January 29
Gravatar of max haughtonPosted by max haughton
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max haughton
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On Sunday, 29 January 2023 at 21:45:11 UTC, Ruby the Roobster wrote:

>

I'm trying to do something like

void main()
{
    auto d = &c;
    *d.writeln;
}

void c()
{
}

In an attempt to get the hexadecimal representation of the machine code of a function. Of course, function pointers cannot be dereferenced. What do?

Furthermore, I would like to be able to do the same for an asm statement.

The function pointer can be casted to a pointer type. It is worth saying, however, that it is not trivial to find where the end of a function is. In X86 it's not even trivial to find the end of an instruction!

If you'd just like the bytes for inspection, you could use a tool like objdump. For more complicated situations you will need to use a hack to tell you where the end of a function is.

January 29
Gravatar of Ali ÇehreliPosted by Ali Çehreli
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Ali Çehreli
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On 1/29/23 14:19, max haughton wrote:

> it is not trivial to find where the *end* of a
> function is

I suspected as much and did run ...

> objdump

... to fool myself into thinking that 0xc3 was <end>. Well, arguments e.g. pointer values can have 0xc3 bytes in them. So, yes, I am fooled! :)

Ali