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.

>>38
Are you using gcc?

>>37
Fucking moron. See >>39 and >>40

>>39-41
So you're saying that language is gnu89? The program is still then undefined you fucking retards.

41 posts in 40 minutes. What the hell, /prog/.

>>42
Just gtfo asspie

>>44
Are you angry because your code is shit?

>>43
>and no answer to OP
;_;

>>46
The answer is undefined you fucking retard are you blind?

>>45
Of course it is shit, it is intentionally shit. That is the point. YOU ARE TOO RETARDED TO FIGURE IT OUT.

>>48
I have already figured it out you fucking retard, it's UNDEFINED.

>>49
facepalm

>>49
Not sure if troll, but
>what is the output of this code WHEN COMPILED WITH GCC AND RAN ON AN INTEL ARCHITECTURE
It is kind of implicit in the question.

http://nickgeoghegan.net/programming/c-can-be-crazy

>>51
It's still undefined.

>>53
Dude. Stop. Just stop.

>>53
What the hell is wrong with you dude?

>>54,55
There is nothing wrong with me you dumb Jew, what the fuck is wrong with you? How the hell is undefined a hard concept to get?

>>56
Confirmed for autistic faggot

>>57
You mad that your code is undefined?

And you all think that I'm out of control....

>>58
The only thing you're accomplishing is to confirm that you aren't clever enough to actually objdump the code and step through it to figure what is going on.

Forever a code monkey. Now go back to your scripting languages.

>>59
For all we know, this is you.

>>60
How may I objdump something that doesn't compile?

>>61
It's not Kodak, I can assure you.

>>61
Nah. I don't write like that.

>>62
By compiling it with the correct compiler, e.g. one proposed in the comments.

>>60
Why wouldn't you just use gdb and step through the source code?

>>66
Of course, you could always use gdb. But gdb gets a bit confused when the symbols are stripped and the function is outside the .text section

>>67
So why are you stripping the symbols?

So this is OS specific, compiler specific, processor specific, compiler flags specific code?

>>69
Yep. Not so much OS specific as architecture specific, compiler and compiler specific code though.

>>69
Not OS specific, but processor and compiler specific. Yes. Or, actually, to be more correct, processor and assembler specific code.

>>52
This.

The first 32 characters of the char data is a swap function. Actually identical to the link, are you copypastaing OP?

>>71
So those signals are not OS specific?

~/prog$ gcc -o a.out -m32 -O0 -c obscure.c && strings a.out
D$0
D$,1D$<
D$,3D$<
D$,1D$<
goto considered harmfull

>>73
No, those are POSIX. You're correct though, but any POSIX OS should be able to run it.

>>75
Mac OS X doesn't allow executing the const char * data.

>>76
Processor?

Also, does Mac OS X support NX? In that case, it won't run.

>>76
Mac OS X doesn't allow executing the const char * data

Uhh... it this because something like this isn't a value?!!!

>>78
Probably because it is put in a read only section with other strings, and OS X doesn't allow readonly sections to be executed.

>>79
wat

>>39
>>40
The code posted is neither: C,C++,Ada,Fortan nor Java

Please go back to the imageboards you uneducated pieces of shit.

Please learn what the word `undefined' means.
Please learn what reserved keywords mean.
`

>>81
>reserved keyword
That is exactly what it is for. Inline assembly. You are so god damned retarded it hurts.

>>81
Are you back again?

>>81
>hurr wuts assembly durrrrr

>>82-84
Why are you samefagging so much?

>>82
>>83
>>84
Enjoying your non-standard, unportable, undefined code that's shit?

I hope you do realize this code is as it says: `undefined'. The output is not guaranteed to be the same for all people. Can you comprehend that simple statement?

>>86
>same compiler on Intel architecture
Its not going to be different, retard

>>86
No they can't, I have tried.
I'm the person he thinks you are now.

Just ask them show you where __asm is defined in any of the C standards.

>>86-87
samefag samefagging samefag

>>87
There is no way you can guarantee that, that is due to the undefined behavior.

>>87-88
For fuck sake, why do you think it is reserved? That's right, to inline assembly. God you are retarded.

OP, just go back to /g/.

>>90
There is. Same compiler for same architecture will produce same machine code -> same result. It isn't undefined behaviour. __asm doesn't result in undefined behaviour you fucking moron, __asm inlines assembly.

>>87
HURR DURR WE ALL HAVE INTELS AND THE SAME PROCESSOR. HOW DO I PORTABLE CODE.
>>88
see >>74
Your code is undefined, stop acting as if it's not.
Some people can't even compile your code even with the commands you give because it is not standard.

>>91
Read the standard you fucking retard. Any identifier that starts with two leading underscores is reserved, there is nothing in the standard that defines what __asm does or even mentions assembly.
__asm isn't part of C you fucking moron now fuck off back to /g/ with your retarded shit.

FIGHT FIGHT

K&R The C programming language, 2ed page 192. (apendix A)

The following identifiers are reserved for use as keywords (AS keywords[sic!]), and may not be used otherwise: [...]
Some implementations reserve the words fortran and asm.

It means that they ARE keywords. Which is VALID code, for some implementations of C. God you are retarded. Go back to scripting.

>>93
You don't understand, if it's undefined then you can't guarantee that it will produce the same code every time.

>>97
Which is VALID code, for some implementations of C.

YOU ENJOYING THAT UNDEFINED BEHAVIOR?

>>95
ITT: Fucking morons

http://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html

>>99
USE THE COMPILER IN OP. God how autistic are you?