"The GNU Debugger (GDB) is a portable debugger that runs on many
Unix-like systems and works for many programming languages, including C,
C++, ... and partially others."
Briefly
For software development, there are several usual debugging toolbox
on Linux, such as strace, perf and gdb. These are used to
inspect behaviour of newly launched programs or of the already running
ones. In this post, I would like to go through how to debug C/C++
programs for logic errors, segmentation faults and memory leaks on
Docker container shortly.
Docker Container
The C/C++ examples and Dockerfile with gdb tool could be found in gdb-debug-docker
on GitHub.
Build and Run interact
with Docker Image
To build the image with cmake and gdb
1
docker build . -t cpp-debug:0.0.1
To run and interact with above built image
1
docker run -it -v $(pwd)/examples:/mnt cpp-debug:0.0.1 bash
Debug Examples in Docker
Container
To build examples programs
1 2 3 4
$ mkdir build $ cd build $ cmake .. $ make
Logical Error
When we run this logicalError program, which caculates the series
value with following formula, we observated that the result did not
return the expected value. First, we was well done indeed for using gdb
to trace down problems.
1 2 3
$ ./logicalError This program is used to compute the value of the following series : (x^0)/0! + (x^1)/1! + (x^2)/2! + (x^3)/3! + (x^4)/4! + ........ + (x^n)/n!
In gdb, at this point, enter the commands: break, run, next, step,
print, and backtrace. It will look something like this:
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.gnu.org%2Fsoftware%2Fgdb%2Fbugs%2F&data=05%7C01%7C%7Ce9e0213a90144c1ddbad08db0a65526b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115202533025083%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Subavd2vT%2Fo8zcWSni%2BlMco76RBwK%2FeydL49Lo8iDBY%3D&reserved=0>. Find the GDB manual and other documentation resources online at: <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.gnu.org%2Fsoftware%2Fgdb%2Fdocumentation%2F&data=05%7C01%7C%7Ce9e0213a90144c1ddbad08db0a65526b%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115202533025083%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=62EKXX2x7RQD3KrFX7ql9hW3p6%2B1t7ysSk0N2VYnLp8%3D&reserved=0>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from build/logicalError...done. (gdb) b ComputeSeriesValue Breakpoint 1 at 0xc4f: file /mnt/header.cpp, line 20. (gdb) r Starting program: /mnt/build/logicalError warning: Error disabling address space randomization: Operation not permitted This program is used to compute the value of the following series : (x^0)/0! + (x^1)/1! + (x^2)/2! + (x^3)/3! + (x^4)/4! + .... + (x^n)/n! Please enter the value of x : 2
Please enter an integer value for n :3
Breakpoint 1, ComputeSeriesValue (x=2, n=3) at /mnt/header.cpp:20 20 double seriesValue = 0.0; (gdb) n 21 double xpow = 1; (gdb) 23 for (int k = 0; k<=n; k ++) { (gdb) 24 seriesValue += xpow / ComputeFactorial(k); (gdb) 25 xpow = xpow * x; (gdb) 23 for (int k = 0; k<=n; k ++) { (gdb) 24 seriesValue += xpow / ComputeFactorial(k); (gdb) step ComputeFactorial (number=1) at /mnt/header.cpp:7 7 int fact = 0; (gdb) print fact $1 = 0 (gdb) n 12 for (int j = 1; j <= number; j ++) { (gdb) 13 fact = fact * j; (gdb) 12 for (int j = 1; j <= number; j ++) { (gdb) 16 return fact; (gdb) bt #0 ComputeFactorial (number=1) at /mnt/header.cpp:16 #1 0x000055adafea6c7e in ComputeSeriesValue (x=2, n=3) at /mnt/header.cpp:24 #2 0x000055adafea6b4b in main () at /mnt/logicalError.cpp:26
By viewing the stack using backtrace, the root cause of unexpected
value is pointed to the ComputeSeriesValue function. We can see the
value of fact remains to be 0 before it is returned.
Segmentation Fault (core
dumped)
When we run this coreDumped program, We can use gdb to trace
segmentation fault step-by-step.
root@a2c941bd0212:/mnt# gdb build/coreDumped GNU gdb (Ubuntu 8.1.1-0ubuntu1) 8.1.1 Copyright (C) 2018 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fgnu.org%2Flicenses%2Fgpl.html&data=05%7C01%7C%7Cd30dce7b66124f88a92408db0a4df50e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115102207439948%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=M1MI65ZgzOErPVwQosQYnV8c%2F0oZQ2exGqFQZIbVmCg%3D&reserved=0> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.gnu.org%2Fsoftware%2Fgdb%2Fbugs%2F&data=05%7C01%7C%7Cd30dce7b66124f88a92408db0a4df50e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115102207439948%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=MlRYNTm67tKwpHDOpil3knX6D8pMf47I2dq2RElUT0c%3D&reserved=0>. Find the GDB manual and other documentation resources online at: <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.gnu.org%2Fsoftware%2Fgdb%2Fdocumentation%2F&data=05%7C01%7C%7Cd30dce7b66124f88a92408db0a4df50e%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115102207439948%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=LRjiiVsGME0jH6Mc3WaBm%2B2iy3ZlEzGzBpUi3WfknLA%3D&reserved=0>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from build/coreDumped...done. (gdb) r Starting program: /mnt/build/coreDumped warning: Error disabling address space randomization: Operation not permitted
Program received signal SIGSEGV, Segmentation fault. 0x00005598e28b166c in main () at /mnt/coreDumped.cpp:15 15 temp[3] = 'F'; (gdb) bt #0 0x00005598e28b166c in main () at /mnt/coreDumped.cpp:15
By viewing the stack using backtrace, the root cause of segmentation
fault is indicated in the line 15 of coreDumped.cpp.
Here's we can also get the stack for every thread with following
command in gdb
root@a2c941bd0212:/mnt# gdb build/coreDumped GNU gdb (Ubuntu 8.1.1-0ubuntu1) 8.1.1 Copyright (C) 2018 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fgnu.org%2Flicenses%2Fgpl.html&data=05%7C01%7C%7C0e6f594d56b5424c1a3608db0a5d5767%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115168250069764%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=m5pT5Xk7qABFXqzZlvRymdmE84Ch%2B7xEmDXxMWhtkRM%3D&reserved=0> This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. Type "show copying" and "show warranty" for details. This GDB was configured as "x86_64-linux-gnu". Type "show configuration" for configuration details. For bug reporting instructions, please see: <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.gnu.org%2Fsoftware%2Fgdb%2Fbugs%2F&data=05%7C01%7C%7C0e6f594d56b5424c1a3608db0a5d5767%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115168250225996%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Tbppnhv8PByr%2FVyergRvhIQru2dMm7U53IJUZp%2B%2BVgY%3D&reserved=0>. Find the GDB manual and other documentation resources online at: <https://aus01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.gnu.org%2Fsoftware%2Fgdb%2Fdocumentation%2F&data=05%7C01%7C%7C0e6f594d56b5424c1a3608db0a5d5767%7C84df9e7fe9f640afb435aaaaaaaaaaaa%7C1%7C0%7C638115168250225996%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=GFGVaYMO1d8T2dcSXJfJwJWRKoQuOtjaYLW2EO2oPQE%3D&reserved=0>. For help, type "help". Type "apropos word" to search for commands related to "word"... Reading symbols from build/coreDumped...done. (gdb) r Starting program: /mnt/build/coreDumped warning: Error disabling address space randomization: Operation not permitted
Program received signal SIGSEGV, Segmentation fault. 0x00005579a99a866c in main () at /mnt/coreDumped.cpp:15 15 temp[3] = 'F'; (gdb) thread apply all bt full
Thread 1 (process 209): #0 0x00005579a99a866c in main () at /mnt/coreDumped.cpp:15 temp = 0x5579a99a8734 "Paras" i = 0
By viewing the above stack using backtrace, the root cause of
segmentation fault is also indicated in the line 15 of coreDumped.cpp
and show every thread in gdb.
Memory Leak
When we run this memoryLeak program, gdb is not able to point out the
memory leak issue. However, we don't need to do anything special to use
valgrind, just call it for a build of program with an argument
--leak-check=yes to see whether there are potential risks of memory
leak, taken from C++
Assignment Overloading and Valgrind Memcheck.
root@a2c941bd0212:/mnt# valgrind --leak-check=yes build/memoryLeak ==206== Memcheck, a memory error detector ==206== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==206== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==206== Command: build/memoryLeak ==206== ==206== ==206== HEAP SUMMARY: ==206== in use at exit: 12 bytes in 1 blocks ==206== total heap usage: 2 allocs, 1 frees, 72,716 bytes allocated ==206== ==206== 12 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==206== at 0x4C3289F: operator new[](unsigned long) (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so) ==206== by 0x10868B: main (memoryLeak.cpp:3) ==206== ==206== LEAK SUMMARY: ==206== definitely lost: 12 bytes in 1 blocks ==206== indirectly lost: 0 bytes in 0 blocks ==206== possibly lost: 0 bytes in 0 blocks ==206== still reachable: 0 bytes in 0 blocks ==206== suppressed: 0 bytes in 0 blocks ==206== ==206== For counts of detected and suppressed errors, rerun with: -v ==206== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
By viewing the memory profile from valgrind, it identifies the
bottlenecks of definitely lost in the line 3 of memoryLeak.cpp.
Due to the most time on my job, we need to type many git command
lines. So that this article is used to sort several git commands
frequently used for easily searching.
"Most players gain pleasure from feeling accepted or belonging to the
group. The good player however, gains pleasure from his ability to cope
with the realities of the game"
In our daily life, most of us usually use Google Map or Apple Maps to help us to
navigate to a place. We can see traffic info, public transit and also
choose our mode of transportation.
"After going on your life-changing journey, you now realize that you
don’t want what you thought you wanted. What you really wanted was
inside you all along."
The HTML canvas can be used for sketching/drawing by mouse. The
canvas API provides a means for drawing graphics via JavaScript and the
HTML element. It largely focuses on 2D graphics. In this post, I would
like to describe how to quickly go about implementing this.
The HTML canvas can be used for sketching/drawing either by mouse or by touch. In the previous post, I quickly discuss how to use Canvas API to implement a canvas with mouse sketching. In this post, I would like to describe how go about implementing for sketching/drawing by mouse and touch.
Either computer data storage or telecommunication, regardless of the
data storages and transmission, is non-zero probabilities that the data
could be changed while it's being stored or transmitted. There is always
a code-word with block length without free bit-errors. That means the
data probably could be changed while it is being processed or
transmitted. If the machine can't locate the position of the error and
correct it, the information might be lost forever.
"Graph theory is the study of graphs, which are mathematical
structures used to model pairwise relations between objects. A graph in
this context is made up of vertices (also called nodes or points) which
are connected by edges (also called links or lines). Graphs are one of
the principal objects of study in discrete mathematics." ... from Wiki
page.
