compiling and running a c program using exec() - c

I am writing a program using execv() that compiles and runs another program. I've written up a simple C program named helloWorld.c that when executed outputs, "Hello world," and a second file named testExec.c that is supposed to compile and run helloWorld.c. I've been looking around everywhere to find a way to do this, but I haven't found any answers. The code in testExec.c is:
#include <stdio.h>
#include <unistd.h>
int main(){
char *args[] = {"./hellWorld.c", "./a.out", NULL};
execv("usr/bin/cc", args);
return 0;
}
testExec.c compiles with no errors. However, when I run it I get an error that says, "fatal error: -fuse-linker-plugin, but liblto_plugin.so not found. compilation terminated." Which I think means helloWorld.c is being compiled but when it comes time to run helloWorld.c this error is thrown. I thought maybe that was because I had a.out and helloWorld.c prefaced with './'. I removed './' from both, then either one individually, and still no luck.
I also did 'sudo apt-get install build-essential' along with 'sudo apt-get install gcc'. I wasn't sure if that would resolve the issue but I really wasn't sure what else to try. Anyway, any help would be appreciated!

You're missing the leading slash when calling cc.
Also, the first argument in the argument list is the name of the executable. The actual arguments come after that. You're also not using -o to specify the name of the output file.
#include <stdio.h>
#include <unistd.h>
int main(){
char *args[] = {"cc", "-o", "./a.out", "./hellWorld.c", NULL};
execv("/usr/bin/cc", args);
return 0;
}
EDIT:
The above only compiles. If you want to compile and run, you can do this:
#include <stdio.h>
#include <unistd.h>
int main(){
system("cc -o ./a.out ./hellWorld.c");
execl("./a.out", "a.out", NULL);
return 0;
}
Although this is probably best done as a shell script:
#!/bin/sh
cc -o ./a.out ./hellWorld.c
./a.out

Related

Simple C Program Lags [Homework]

For an assignment I have we are to find vulnerabilities in a certain C program and exploit them using various buffer overflow attacks. However when I run the .out file in the terminal with it's input argument it just stalls and doesn't do anything.
Even when I run GDB, that just lags too. I'm not looking for a solution to the assignment, I'm just looking for reasons why it's not running?
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
void partialwin()
{
printf("Achieved 1/2!\n");
}
void fullwin(){
printf("Achieved 2/2\n");
}
void vuln(){
char buffer[36];
gets(buffer);
printf("Buffer contents are %s\n",buffer);
}
int main(int argc,char**argv){
vuln();
}
Providing your sourc file is called assignment1.c and you're using gcc this should work, $ being your command prompt (which could be different on your platform)
$ gcc assignment1.c
$ a.out
Hello
Buffer contents are Hello
$

gcc -pthread no such fiile or directory ex_thread_creation

I'm trying to print infinite lines "Hello, how are you", "I'm fine, and you"
first I use command "vim ex_thread_creation"
then I enter following the code:
#include <pthread.h>
#include <stdio.h>
void *thread_print(void * messenge)
{
while(1) {
printf("Hello, How are you?\n");
}
}
int main()
{
pthread_t idthread;
pthread_create( &idthread,NULL, &thread_print, NULL);
while(1) {
printf("I’m fine, and you?\n");
}
return 0;
}
then I use gcc ex_thread_creation.c -pthread ex_thread_creation
then I meet the error: no such file or directory ex_thread_creation.
someone help me, please
edit 1: after I change -pthread to -o I meet another error: ex_thread_creation.c:(.text+0x4a): undefined reference to pthread_create collect2: error: old returned 1 exit status
There are several problems with your approach.
Regarding your gcc issue, the correct command would be:
gcc ex_thread_creation.c -o ex_thread_creation -lpthread
The -o flag stands for outfile or the file resulted from compiling the source file.
Regarding your code there are several issues too other than your code indentation.
The lines "Hello, how are you" and "I'm fine, and you" might not appear one after the other as intended. The output may appear malformed (the lines being intertwined) or the order could be wrong (Hello -> Hello -> I'm fine -> I'm fine).
If you want to keep the output as intended in your question, I suggest you use synchronization mechanisms.
after research a bit longer, i've found the answer,
the correct command is: gcc -pthread -o term term.c
thank you for reading

Syntax error reported in basic C code - what is wrong?

The code is given below.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int main ( int argc, char *argv[] )
{
//FILE *fps;
char secret[512] =" ";
FILE *fps = fopen("/etc/comp2700/share/secret", "r");
if(fps == NULL)
{
printf("Secret file not found\n");
return 1;
}
fgets(secret, 512, fps);
printf("Secret: %s\n", secret);
fclose(fps);
return 0;
}
When I am trying to run this program it is repeatedly throwing the following error:
./attack1.c: line 4: syntax error near unexpected token `('
./attack1.c: line 4: `int main ( int argc, char *argv[] )'
You need to compile your source file with gcc as follows
gcc -o attack attack1.c
then run it with
./attack
You should read up on the difference between compiled versus interpreted languages.
There is a short video here explaining the difference.
You cannot run your C program from the command line as ./attack1.c. Normally the shell would refuse to execute the C source file because it should not have execute permission, but for some reason, on your system, it must have the x bits and is read by the default shell as a script.
Of course this fails because attack1.c contains C code, not a command file. Note that the #include lines are interpreted as comments by the shell and the error only occurs at line 4.
To run a C program, you must first compile it to produce an executable:
gcc -Wall -o attack1 attack1.c
And then run the executable if there were no compilation errors:
./attack1
You can combine these commands as
gcc -Wall -o attack1 attack1.c && ./attack1
First, you need to compile the attack.c code using the following command:
gcc attack.c
This will create one executable file a.out which you can run using the following command:
./a.out
Hope this helps you.

Why do I get a syntax error when I try to cross compile libperl for mips64?

I'm trying to cross compile net-snmp for mips64, and in order to do that I need the libperl library. I tried to configure libperl for mips64 using the following command:
./Configure -Dcc=/home/toby/x-tools/mips64-n64-linux-gnu/bin/mips64-n64-linux-gnu-gcc -Dprefix=/home/toby/perl
But I got the following error:
Checking your choice of C compiler and flags for coherency...
I've tried to compile and run the following simple program:
#include <stdio.h>
int main() { printf("Ok\n"); return(0); }
I used the command:
/home/toby/x-tools/mips64-n64-linux-gnu/bin/mips64-n64-linux-gnu-gcc -o try -O -I/usr/local/include try.c
./try
and I got the following output:
./try: 1: Syntax error: "(" unexpected
The program compiled OK, but exited with status 2.
(The supplied flags or libraries might be incorrect.)
You have a problem. Shall I abort Configure [y]
How can I fix this?
I'd turn:
#include <stdio.h>
int main() { printf("Ok\n"); return(0); }
Into:
#include <stdio.h>
int main() {
printf("Ok\n");
return(0);
}
And then run the compile command by hand to see which line really contains the syntax error.
That looks like an error from your shell and not the compiler. Particularly because gcc doesn't return "status 2" for a syntax error, but bash does. The problem happens because you have cross compiled a program called ./try for mips64. How do you expect ./Configure to execute it on your host pc? – indiv

editline/history.h and editline/readline.h not found/working on macOS when trying to compile with developer tools installed already

I am working on this tutorial on building your own LISP (http://www.buildyourownlisp.com/chapter4_interactive_prompt) and for some reason when I try to compile I get this:
REPL.c:4:10: fatal error: 'editline/readline.h' file not found
#include <editline/history.h>
^
1 error generated.
I have installed the macOS developer tools, and brew is showing readline is installed and it doesn't know what to do when I try brew install editline.
This is my code:
1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <editline/readline.h>
4 #include <editline/history.h>
5
6 int main(int argc, char** argv) {
7
8 /* version/exit info */
9 puts("Edward Version 0.0.1");
10 puts("Press Ctrl+c to Exit\n");
11
12 /* endless loop for main REPL */
13 while (1) {
14 /* output prompt and read line */
15 char* input = readline("lispy> ");
16
17 /* put input in history */
18 add_history(input);
19
20 /* Echo input back */
21 printf("No you're a %s\n", input);
22
23 /* free input */
24 free(input);
25 }
26 return 0;
27 }
It is obviously very basic, but I really want to get this project rolling so I'm hoping I can figure this out. This is what I'm using to compile:
cc -std=c99 -Wall REPL.c -ledit -o REPL
Include only
#include <editline/readline.h>
which should exist if the command line tools are installed. This file contains the
"readline wrapper" for libedit, including the history functions as well.
An include file <editline/history.h> does not exist on OS X.
I tested your code with that modification, and it compiled and ran without problems.
Using OSX Yosemite. I removed #include<editline/history.h>
and then used cc -std=c99 -Wall test.c -ledit -o test
Works fine now
I'm on El Capitan,
Remove #include <editline/history.h>,
and use cc -std=c99 -Wall test.c -ledit -o test works for me.
Add the flag -ledit before the output flad, it's a linking process, allows the compiler to directly embed calls to editline in your program. Or, you'll get the below error message,
Undefined symbols for architecture x86_64:
"_add_history", referenced from:
_main in prompt-086f90.o
"_readline", referenced from:
_main in prompt-086f90.o
ld: symbol(s) not found for architecture x86_64
I'm on Ubuntu 14.04.
try this:
sudo apt-get install libeditline-dev
and include like this:
#include <editline.h>
finally compile like this:
add -leditline in the flag
I hope this can help.
I'm on OSX Mavericks and removing the line worked for me:
#include <editline/history.h>
The solution for those following along on FreeBSD (might work on other Unices as well):
#include <stdio.h>
#include <stdlib.h>
#include <readline/readline.h>
#include <readline/history.h>
...
And run:
$ cc test.c -Wall -std=c99 -lreadline -o test
Without "-lreadline" in the compile step it is not linked in and you will get errors about undefined reference to "readline" function.
I started in on Build your own list and ran into the same problem.
None of the above answers worked for me. After a little research I found out that macOs doesn't have the gnu readline library that provides the readline functions, Different versions of MacOs provide emulation of readline using a library called editline. to begin...
man editline
#include <histedit.h>
Ok, editline gives you some structs for line input and history,
and functions to operate on them. First you have to instantiate these structs. The documentation for editline is not very helpful because it doesn't contain any examples. Apple makes the header file available so that helps a little. http://www.opensource.apple.com/source/libedit/libedit-13/src/histedit.h
I am new to this and it was still pretty confusing to me. there is some version of the source code to libedit available as a debian package. Fortunately someone wiser than I has already dug into it and implemented a command line using lbedit. His code is here: https://www.cs.utah.edu/~bigler/code/libedit.html.
I took Mr Bigler's code, and the code from Build your own list, and put them together to get this.
/* repl-macos.c
* Repl code example from builyourownlisp.com
* Modified by NB aug 2017
* Code example for editline from
* www.cs.utah.edu/~bigler/code/libedit.html
*/
#include <stdio.h>
#include <string.h>
#include <histedit.h>
char* prompt(EditLine *e){
return "lispy> ";
}
int main(int argc, char** argv){
EditLine *el; // Line editor state
History *herstory; // the rest is history
// Temp Variables
int count;
const char *usrin;
int keepreading = 1;
HistEvent ev;
// Initialize the editline state
el = el_init(argv[0], stdin, stdout, stderr);
el_set(el, EL_PROMPT, &prompt);
el_set(el, EL_EDITOR, "emacs");
// Initialize history
herstory = history_init();
if(!herstory){
fprintf(stderr, "Couldn't initialize history\n");
return 1;
}
//set history size
history(herstory, &ev, H_SETSIZE, 800);
// Set up the call back functions for history functionality
el_set(el, EL_HIST, history, herstory);
puts("Begin moLisp interpreter");
puts("Type 'exit' at prompt to exit");
while(keepreading){
usrin = el_gets(el, &count);
// add the command to the history, and echo it back to the user
if(count > 0){
history(herstory, &ev, H_ENTER, usrin);
if(strcmp(usrin, "exit\n"))
printf("No, You're a %s", usrin);
else{
puts("bye");
--keepreading;
}
}
}
// Clean up memory
// by freeing the memory pointed to within the structs that
// libedit has created.
history_end(herstory);
el_end(el);
return 0;
}
Notice: The instantiation of the structs that are used happens outside of
the while loop, and so do the functions that free the memory those structs are using. Because of this, I added the command to exit, otherwise I think there's a memory leak if the only way to exit the while loop is by interrupting the program. To compile:
gcc repl-macos.c -ledit -Wall -o repl-edit
-ledit is needed to link editline
If it has any relevance, I am using macOs 10.4.11
and here's my compiler, output of
gcc --version
powerpc-apple-darwin8-gcc-4.0.0 (GCC) 4.0.0 20041026 (Apple Computer, Inc. build 4061)
Now the only problem with this, and the book points this out, is that
c-code is supposed to be portable and this isn't. The next step would be to add preprocessor directives so that it uses readline on linux and editline on macos.
If you are on ubuntu add the editline library
sudo apt-get install libtedit-dev
On Debian Buster 10, I had to install the package with:
sudo apt install libeditline-dev
Instead of:
#include <editline/readline.h>
#include <editline/history.h>
I just included:
#include <editline.h>
ran the program with -leditline flag and worked perfectly.

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