Code explanation

Can somebody explain why this code outputs what it does?

// tested with Core 2 Duo, Core 2 Quad and Xeon
// tested with gcc4.1.2 gcc4.4.3 and gcc4.6.1
// compile with: gcc -O0 -m32
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <setjmp.h>

jmp_buf p;
void (*q)();

const char *data =
    "\x8b\x44\x24\x04\x8b\x5c\x24\x08"
    "\x8b\x00\x8b\x1b\x31\xc3\x31\xd8"
    "\x31\xc3\x8b\x4c\x24\x04\x89\x01"
    "\x8b\x4c\x24\x08\x89\x19\xc3\x90"
    "\x55\x89\xe5\x8b\x45\x04\xc9\xc3"
    "\x55\x90\x90\x89\xe5\x90\x90\x90"
    "\x8b\x45\x08\x89\x45\x04\xc9\xc3"
    "\x60\x09\x0e\x13\x14\x01\x0c\x0c"
    "\xc0\x07\x05\x0e\x14\x0f\x0f\x60"
    "\x00\x67\x6f\x74\x6f\x20\x63\x6f"
    "\x6e\x73\x69\x64\x65\x72\x65\x64"
    "\x20\x68\x61\x72\x6d\x66\x75\x6c"
    "\x6c\x00\x90\x90\x1c\x1b\x0a\x20";

int f(int x)
{
    static int b = 0; static int s = 0;
    int a = 0, t;
    if (!s) {
        a = b; b = x;
    } else {
        a = x; t = b;
        do {
            a ^= b;
            b = (a^b) & b;
            b <<= 1;
        } while (b);
        b = t;
    }
    s = (s+1) % 2;
    return a;
}

int g(int i, int *j)
{
    *j = i;
    i = (int) putchar;
    if (*j == (48 << 1)) 
        __asm volatile (
                "movl 8(%ebp),%eax;"
                "leave;"
                "ret"
                );
    return (int) puts;
}

void h(int i)
{
    int b;
    q = (void(*)()) g(i++[data],&b);
    for (f(b);*(data+i)!=b;++i,f(b))
        q(f(i[data])%0xff);
}

void sh(int s)
{
    if (s == 010)
        ((void(*)())g(s,&s))("F");
    longjmp(p,s);
}

int main(void)
{
    int base, addr = 0xffffffff, offs = 16;
    int a = 11, b = 32, i = 25;
    int s = 8, t = 1, u = 4;
    ((void(*)()) data)(&a,&b);
    ((void(*)()) data)(&b,&t);
    ((void(*)()) data)(&t,&s);
    addr ^= a;
       a ^= addr;
    addr ^= a;
    base = ((int(*)())data+addr)();
    if (a == -1)
        goto over;
    puts("A");

    base = (1<<3) | ((f(addr) + f(offs)) & ~0xff);
    h(base+addr+offs);
    exit(0);

over:
    signal(t,sh);signal(s,sh);signal(u,sh);

    if (!(s = setjmp(p))) {
        q = (void(*)()) g(0x30, &a);
        q(data + a + i);
        s = a / (b-1);
        puts("B");
    } else if (s == 0xb) {
        puts("C");
        ((int(*)(int)) data+addr+(offs/2))(base);
    } else {
        puts("D");
        *((int*) base+s) = 0xffffffff;
    }
   
    puts("E");
    return 1;
}

I see no code in [code] tags.

>>2
Sorry, I'm new to the text boards.

http://pastebin[dot]com/uPHf2wZU

It outputs Segmentation fault, I guess this has something to do with an address being mishandled.


const char *data =
    "\x8b\x44\x24\x04\x8b\x5c\x24\x08"
    "\x8b\x00\x8b\x1b\x31\xc3\x31\xd8"
    "\x31\xc3\x8b\x4c\x24\x04\x89\x01"
    "\x8b\x4c\x24\x08\x89\x19\xc3\x90"
    "\x55\x89\xe5\x8b\x45\x04\xc9\xc3"
    "\x55\x90\x90\x89\xe5\x90\x90\x90"
    "\x8b\x45\x08\x89\x45\x04\xc9\xc3"
    "\x60\x09\x0e\x13\x14\x01\x0c\x0c"
    "\xc0\x07\x05\x0e\x14\x0f\x0f\x60"
    "\x00\x67\x6f\x74\x6f\x20\x63\x6f"
    "\x6e\x73\x69\x64\x65\x72\x65\x64"
    "\x20\x68\x61\x72\x6d\x66\x75\x6c"
    "\x6c\x00\x90\x90\x1c\x1b\x0a\x20";

\x90Nop
Stopped reading right there. Is this a fancy stack smasher?


// tested with Core 2 Duo, Core 2 Quad and Xeon
// tested with gcc4.1.2 gcc4.4.3 and gcc4.6.1
// compile with: gcc -O0 -m32
#include <stdio.h>
#include <stdlib.h>
#include <signal.h>
#include <setjmp.h>

jmp_buf p;
void (*q)();

const char *data =
    "\x8b\x44\x24\x04\x8b\x5c\x24\x08"
    "\x8b\x00\x8b\x1b\x31\xc3\x31\xd8"
    "\x31\xc3\x8b\x4c\x24\x04\x89\x01"
    "\x8b\x4c\x24\x08\x89\x19\xc3\x90"
    "\x55\x89\xe5\x8b\x45\x04\xc9\xc3"
    "\x55\x90\x90\x89\xe5\x90\x90\x90"
    "\x8b\x45\x08\x89\x45\x04\xc9\xc3"
    "\x60\x09\x0e\x13\x14\x01\x0c\x0c"
    "\xc0\x07\x05\x0e\x14\x0f\x0f\x60"
    "\x00\x67\x6f\x74\x6f\x20\x63\x6f"
    "\x6e\x73\x69\x64\x65\x72\x65\x64"
    "\x20\x68\x61\x72\x6d\x66\x75\x6c"
    "\x6c\x00\x90\x90\x1c\x1b\x0a\x20";

int f(int x)
{
    static int b = 0; static int s = 0;
    int a = 0, t;
    if (!s) {
        a = b; b = x;
    } else {
        a = x; t = b;
        do {
            a ^= b;
            b = (a^b) & b;
            b <<= 1;
        } while (b);
        b = t;
    }
    s = (s+1) % 2;
    return a;
}

int g(int i, int *j)
{
    *j = i;
    i = (int) putchar;
    if (*j == (48 << 1))
        __asm volatile (
                "movl 8(%ebp),%eax;"
                "leave;"
                "ret"
                );
    return (int) puts;
}

void h(int i)
{
    int b;
    q = (void(*)()) g(i++[data],&b);
    for (f(b);*(data+i)!=b;++i,f(b))
        q(f(i[data])%0xff);
}

void sh(int s)
{
    if (s == 010)
        ((void(*)())g(s,&s))("F");
    longjmp(p,s);
}

int main(void)
{
    int base, addr = 0xffffffff, offs = 16;
    int a = 11, b = 32, i = 25;
    int s = 8, t = 1, u = 4;
    ((void(*)()) data)(&a,&b);
    ((void(*)()) data)(&b,&t);
    ((void(*)()) data)(&t,&s);
    addr ^= a;
       a ^= addr;
    addr ^= a;
    base = ((int(*)())data+addr)();
    if (a == -1)
        goto over;
    puts("A");

    base = (1<<3) | ((f(addr) + f(offs)) & ~0xff);
    h(base+addr+offs);
    exit(0);

over:
    signal(t,sh);signal(s,sh);signal(u,sh);

    if (!(s = setjmp(p))) {
        q = (void(*)()) g(0x30, &a);
        q(data + a + i);
        s = a / (b-1);
        puts("B");
    } else if (s == 0xb) {
        puts("C");
        ((int(*)(int)) data+addr+(offs/2))(base);
    } else {
        puts("D");
        *((int*) base+s) = 0xffffffff;
    }
  
    puts("E");
    return 1;
}

The output is undefined as it uses a lot of non-portable conventions.

>>5
>XOR, XOR, XOR
It looks like a swap function to me

>>7
It says in the comments what to compile it with on where

I'm not running that.

Lots of people who can't read the comments here.

>>10
>>9
>>8
>>7
>>6
>>5
>>4
goto considered harmfull
F
D
C
A
install gentoo

>>9
Really? Where does it say where it should be compiled?

>core 2 duo, core 2 quad, xeon
Pretty clear you need to run it on a IA32/x86_64 of some sort.

>>9
Well you are a dumb Jew.

On my machine it outputs Segmentation fault, I guess that's because it relies on undefined behavior.

>>9
I specialize in the standard, not some obscure toy subset language.

>>16
>not doing hw specific coding ever
why are you even here

>>15
unable to compile with gcc -m32 -O0


/ tested with Core 2 Duo, Core 2 Quad and Xeon
 // tested with gcc4.1.2 gcc4.4.3 and gcc4.6.1
 // compile with: gcc -O0 -m32
 #include <stdio.h>
 #include <stdlib.h>
 #include <signal.h>
 #include <setjmp.h>

 jmp_buf p;
 void (*q)();

 const char *data =
     "\x8b\x44\x24\x04\x8b\x5c\x24\x08"
     "\x8b\x00\x8b\x1b\x31\xc3\x31\xd8"
     "\x31\xc3\x8b\x4c\x24\x04\x89\x01"
     "\x8b\x4c\x24\x08\x89\x19\xc3\x90"
     "\x55\x89\xe5\x8b\x45\x04\xc9\xc3"
     "\x55\x90\x90\x89\xe5\x90\x90\x90"
     "\x8b\x45\x08\x89\x45\x04\xc9\xc3"
     "\x60\x09\x0e\x13\x14\x01\x0c\x0c"
     "\xc0\x07\x05\x0e\x14\x0f\x0f\x60"
     "\x00\x67\x6f\x74\x6f\x20\x63\x6f"
     "\x6e\x73\x69\x64\x65\x72\x65\x64"
     "\x20\x68\x61\x72\x6d\x66\x75\x6c"
     "\x6c\x00\x90\x90\x1c\x1b\x0a\x20";

 int f(int x)
 {
     static int b = 0; static int s = 0;
     int a = 0, t;
     if (!s) {
         a = b; b = x;
     } else {
         a = x; t = b;
         do {
             a ^= b;
             b = (a^b) & b;
             b <<= 1;
         } while (b);
         b = t;
     }
     s = (s+1) % 2;
     return a;
 }

 int g(int i, int *j)
 {
     *j = i;
     i = (int) putchar;
     if (*j == (48 << 1)) 
         __asm volatile (
                 "movl 8(%ebp),%eax;"
                 "leave;"
                 "ret"
                 );
     return (int) puts;
 }

 void h(int i)
 {
     int b;
     q = (void(*)()) g(i++[data],&b);
     for (f(b);*(data+i)!=b;++i,f(b))
         q(f(i[data])%0xff);
 }

 void sh(int s)
 {
     if (s == 010)
         ((void(*)())g(s,&s))("F");
     longjmp(p,s);
 }

 int main(void)
 {
     int base, addr = 0xffffffff, offs = 16;
     int a = 11, b = 32, i = 25;
     int s = 8, t = 1, u = 4;
     ((void(*)()) data)(&a,&b);
     ((void(*)()) data)(&b,&t);
     ((void(*)()) data)(&t,&s);
     addr ^= a;
        a ^= addr;
     addr ^= a;
     base = ((int(*)())data+addr)();
     if (a == -1)
         goto over;
     puts("A");

     base = (1<<3) | ((f(addr) + f(offs)) & ~0xff);
     h(base+addr+offs);
     exit(0);

 over:
     signal(t,sh);signal(s,sh);signal(u,sh);

     if (!(s = setjmp(p))) {
         q = (void(*)()) g(0x30, &a);
         q(data + a + i);
         s = a / (b-1);
         puts("B");
     } else if (s == 0xb) {
         puts("C");
         ((int(*)(int)) data+addr+(offs/2))(base);
     } else {
         puts("D");
         *((int*) base+s) = 0xffffffff;
     }
    
     puts("E");
     return 1;
 }

>>15
>>7

 // tested with Core 2 Duo, Core 2 Quad and Xeon
 // tested with gcc4.1.2 gcc4.4.3 and gcc4.6.1
 // compile with: gcc -O0 -m32

Seriously, /prog/? You disappoint me. Even /g/ managed to compile and run it at least

__asm is a reserved identifier, so your code isn't even C, the parts of the code that might C is full of undefined behavior.

In short you are a fucking retard who should fuck off back to /g/.

>>21
Well, that's prove that we're superior to /g/ as we will not compile and run suspiciously looking code(and I'm not going to setup new virtual machine just because I got dubs.)

Only /g/ can be so stupid. And /b/, speaking of which /polecat kebabs/.

>>22
>hurr i have never done any hw specific code

>>23
you can run it in a jail or you can even do a hex dump, no running involved

And since >>22 stole dubs while I was writing reply, I'm inclined to setup vm even less now.

>>26
just set up a jail, vm isn't required

>>21
I ain't gonna switch off from my super ricer desktop to my
obscure gcc compilin desktop just to see a stack smashing warning.

>>28
>stack smash
>implying you need to reboot after one
lulwut

>>24
I have but I assure you it was a lot better than this undefined piece of shit.

~/prog$ gcc -m32 -O0 obscure.c && ./a.out
goto considered harmfull
F
D
C
A
install gentoo

>>30
The code is intentionally retarded fuckwit

>>30
But you're still not clever enough to figure it out

>>32,33
Okay listen you fucking retard, read this and understand it.

__asm is a reserved identifier so the code is not C

The parts of the code that might be C, is full of undefined behavior, so there is nothing to figure out, what it outputs is undefined.

There you go fucknut now fuck off back to /g/ you stupid piece of shit.

>>34
>__asm is a reserved identifier so the code is not C
And exactly what is your point? Nowhere did OP claim that it was C.

>>34
Dude, no where does anyone claim that it is C. OP asked for the program flow. It certainly does compile and run. You're just being an ignorant dick.

>>35
That's implicit by asking us to compile it with a C compiler, are you mentally challenged?

>>36
It doesn't compile on my machine.

>>37
GCC compiles much more than C, you moron. GCC compiles both C and C++, and it also assembles and links. It even supports Java for fuck sake.

GCC is a compiler suite, not a C compiler. You are a fucking idiot and should kill yourself

>>37
GCC isn't a C compiler, it is the GNU compiler suite. It supports everything from Ada to Fortran to Java. It is also a assembler, if you haven't noticed.