Debugging tools
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Valgrind is an open source debugging tool that can detect memory leaks, invalid pointer use, and use of uninitialized variables. It works by running the program within its environment. When memory errors are detected, Valgrind will output details on the type of error and location. Wireshark is a packet analyzer that allows inspection of network traffic. It captures packets from selected interfaces and allows analysis of packet information and contents.
![Matteo Virgilio, Politecnico di Torino – 5° May, 2014
4/10
Example: a simple calculator
#include <stdio.h>
#include <stdlib.h>
#define N 1024
int main(int argc, char* argv[])
{
char* buffer;
int op1, op2;
while(1)
{
buffer = (char*)malloc(N*sizeof(char));
printf ("Insert two integers: ");
fgets (buffer, N, stdin);
sscanf (buffer, "%d %d", &op1, &op2);
printf ("Result=%dn", op1+op2);
}
}
gcc –g –o calc calc.c](https://image.slidesharecdn.com/debuggingtools-140519023750-phpapp02/85/Debugging-tools-4-320.jpg)
![Matteo Virgilio, Politecnico di Torino – 5° May, 2014
6/10
The revised code
#include <stdio.h>
#include <stdlib.h>
#define N 1024
int main(int argc, char* argv[])
{
char* buffer;
int op1, op2;
while(1)
{
buffer = (char*)malloc(N*sizeof(char));
printf ("Insert two integers: ");
fgets (buffer, N, stdin);
sscanf (buffer, "%d %d", &op1, &op2);
printf ("Result=%dn", op1+op2);
free (buffer);// Release the allocated memory to the OS
}
}](https://image.slidesharecdn.com/debuggingtools-140519023750-phpapp02/85/Debugging-tools-6-320.jpg)
Debugging tools
- 1. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 1/10 Debugging Tools Matteo Virgilio Politecnico di Torino matteo.virgilio@polito.it
- 2. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 2/10 Valgrind • Valgrind is an open source tool for memory debugging and it is available for Linux. • Can be exploited to: Find memory leaks; Find Invalid Pointer Use Detect The Use Of Uninitialized Variables Etc etc… • Complete documentation available at: http://valgrind.org/docs/
- 3. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 3/10 Valgrind brief HOWTO 1. Compile your code with –g option in GCC. 2. Run your program within the Valgrind environment. Assuming your program is executed with the following cmd line: ./server 1500 You can simply invoke: valgrind ./server 1500 3. After quitting your program (e.g. Ctrl-C), you will get the Valgrind output.
- 4. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 4/10 Example: a simple calculator #include <stdio.h> #include <stdlib.h> #define N 1024 int main(int argc, char* argv[]) { char* buffer; int op1, op2; while(1) { buffer = (char*)malloc(N*sizeof(char)); printf ("Insert two integers: "); fgets (buffer, N, stdin); sscanf (buffer, "%d %d", &op1, &op2); printf ("Result=%dn", op1+op2); } } gcc –g –o calc calc.c
- 5. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 5/10 Output with Valgrind: memory leak found! mettiu@mettiu-virtual-machine:~/valgrind_example$ valgrind ./calc ==5857== Memcheck, a memory error detector ==5857== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al. ==5857== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info ==5857== Command: ./calc ==5857== Insert two integers: 10 10 Result=20 Insert two integers: ^C==5857== ==5857== HEAP SUMMARY: ==5857== in use at exit: 2,048 bytes in 2 blocks ==5857== total heap usage: 2 allocs, 0 frees, 2,048 bytes allocated ==5857== ==5857== LEAK SUMMARY: ==5857== definitely lost: 1,024 bytes in 1 blocks ==5857== indirectly lost: 0 bytes in 0 blocks ==5857== possibly lost: 0 bytes in 0 blocks ==5857== still reachable: 1,024 bytes in 1 blocks ==5857== suppressed: 0 bytes in 0 blocks ==5857== Rerun with --leak-check=full to see details of leaked memory ==5857== ==5857== For counts of detected and suppressed errors, rerun with: -v ==5857== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
- 6. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 6/10 The revised code #include <stdio.h> #include <stdlib.h> #define N 1024 int main(int argc, char* argv[]) { char* buffer; int op1, op2; while(1) { buffer = (char*)malloc(N*sizeof(char)); printf ("Insert two integers: "); fgets (buffer, N, stdin); sscanf (buffer, "%d %d", &op1, &op2); printf ("Result=%dn", op1+op2); free (buffer);// Release the allocated memory to the OS } }
- 7. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 7/10 Output with Valgrind: everything ok! mettiu@mettiu-virtual-machine:~/valgrind_example$ valgrind ./calc ==5884== Memcheck, a memory error detector ==5884== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al. ==5884== Using Valgrind-3.8.1 and LibVEX; rerun with -h for copyright info ==5884== Command: ./calc ==5884== Insert two integers: 10 10 Result=20 Insert two integers: ^C==5884== ==5884== HEAP SUMMARY: ==5884== in use at exit: 1,024 bytes in 1 blocks ==5884== total heap usage: 2 allocs, 1 frees, 2,048 bytes allocated ==5884== ==5884== LEAK SUMMARY: ==5884== definitely lost: 0 bytes in 0 blocks ==5884== indirectly lost: 0 bytes in 0 blocks ==5884== possibly lost: 0 bytes in 0 blocks ==5884== still reachable: 1,024 bytes in 1 blocks ==5884== suppressed: 0 bytes in 0 blocks ==5884== Rerun with --leak-check=full to see details of leaked memory ==5884== ==5884== For counts of detected and suppressed errors, rerun with: -v ==5884== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
- 8. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 8/10 Wireshark • Wireshark is one of the most famous packet analyzers. • Cross-platform • Simple interaction thanks to the advanced GUI provided • Use wireshark to look at the actual data sent to/by your applications! • http://www.wireshark.org/
- 9. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 9/10 Wireshark brief HOWTO 1. Start wireshark (may require root privileges) 2. Select the correct interface on which to capture (loopback if you are working on your local machine) 3. Start the capture 4. Run your data transfer/program to debug 5. Stop the capture 6. Analyze wireshark output
- 10. Matteo Virgilio, Politecnico di Torino – 5° May, 2014 10/10 An example Packets list Packet information Raw packet representation