Find and solve program errors on Linux (I)

Find and solve program errors on Linux (I)-Linux general technology-Linux programming and kernel information. The following is a detailed description. You can monitor the running user space program in various ways: You can run the debugger for it, debug the program in one step, add print statements, or add tools to analyze the program. This article describes several methods that can be used to debug programs running on Linux. We will review the four debugging problems, including segment errors, memory overflow and leakage, and suspension.

This article discusses four types of Linux program debugging. In the 1st cases, we used two sample programs with memory allocation problems and used MEMWATCH and Yet Another Malloc Debugger (YAMD) tools to debug them. In the 2nd cases, we used the strace utility in Linux, which can track system calls and signals to find out where the program is wrong. In the 3rd cases, we use the Oops function of the Linux kernel to solve segment errors, and show you how to set the kernel source code-level debugger (kgdb ), use the GNU debugger (GNU debugger, gdb) to solve the same problem. The kgdb program is a Linux kernel that uses a serial connection. In 4th cases, we use the magic key sequence provided on Linux to display information about components that cause suspension issues.

Common debugging methods

When your program contains errors, it is very likely that there is a condition somewhere in the code. You think it is true, but it is actually false ). The process of identifying an error is a process in which a certain condition is always believed to be true after an error is found.

The following examples are some types of conditions that you may be certain about:

Somewhere in the source code, a variable has a specific value.

A structure has been correctly set in a given place.

For the given if-then-else statement, the if part is the path to be executed.

When a subroutine is called, it receives its parameters correctly.

Identify the error, that is, determine whether all the above conditions exist. If you are sure that a variable should have a specific value when the subroutine is called, check whether this is the case. If you believe that the if structure will be executed, check whether this is the case. Generally, your assumptions are correct, but eventually you will find a situation that does not match the assumptions. Result, you will find out where an error occurs.

Debugging is a task that you cannot escape. There are many debugging methods, such as printing messages to the screen, using the debugger, or simply considering program execution and carefully figuring out the problem.

Before you fix the problem, you must find its source. For example, for a segment error, you need to know which line of the Code contains the segment error. Once you find an error line in the code, determine the value of the variable in the method, the method of calling the method, and the details about how the error occurs. Using the debugger makes it easy to find all this information. If no debugger is available, you can use other tools. (Note that the debugger may not be provided in the product environment, and the Linux kernel does not have a built-in debugger .)

Practical memory and kernel tools

You can use the debugging tool on Linux to track user space and kernel problems in various ways. Use the following tools and technologies to build and debug your source code:

User space tools:

Memory tools: MEMWATCH and YAMD

Strace

GNU Debugger (gdb)

Magic key sequence

Kernel tools:

Kernel source code-level debugger (kgdb)

Built-in kernel debugger (kdb)

Oops

This article will discuss a type of problem that is hard to find by manually checking the code, and this type of problem only exists in rare cases. Memory Errors usually occur in multiple cases at the same time, and sometimes you can only find Memory Errors After deploying the program.