GDB Debugging ARM U-Boot on QEMU

1 Introduction

QEMU is a generic and open source machine emulator and virtualizer. In this article, we will use it as a machine emulator and run the U-Boot on top of it. It will also be demonstrated about how to debug U-Boot with GDB.

MIPS Exceptions Initialization and Handling on Linux

Exceptions and interrupts are un-expected events that disrupt the normal flow of execution. Interrupts are unexpected events from outside the CPU core. Exceptions are from within the CPU, including memory translation exceptions, cache misses, unusual program conditions such as unaligned loads, system calls and traps, and so on.

MIPS architecture adopts precise exception mechanisms, and make it easy for the software to deal with the exceptions. After any exception, CP0 EPC register points to the correct place to restart execution after the exception is dealt with.

Learning the Linux Boot Memory Allocator (MIPS)

Do you ever look at the report of 'cat /proc/meminfo' and wonder why the reported MemTotal is not equal to the amount of memory you have for the system? The followed is an example report from one of my systems. It shows the total memory is 60860kB (59.4MB) from line 2:

1 # cat /proc/meminfo
2 MemTotal:          60860 kB
3 MemFree:           47448 kB
4 Buffers:               0 kB
5 Cached:             7180 kB
6 SwapCached:            0 kB
7 ... 

which is different from the amount of memory that bootloader gave to kernel, 64MB.

1 ...
2 ## Transferring control to Linux (at address 800042f0) ...
3 ## Giving linux memsize in MB, 64 

Step by step to MIPS assembly

In this article, I am going to introduce how to write MIPS assembly. All the examples introduced will able to be assembled or compiled into actual executable programs. They can be executed on a MIPS machine running Linux. So, let's forget the simulator and come to real world :-P. The first is the most simple program.

MIPS calling convention with GCC

In this article, we are going to learn MIPS calling conventions by examples. And we will focus on the one used by GCC. All the examples will be compiled with GCC flag -mno-abicalls not generating SVR4-style position-independent code. Normally -mabicalls should be used, we disable it for the simplification of assembly codes.

C99 Features

Here is a simple example demonstrating some of the C99 features. It is a test program I wrote for learning from C99 standard. Although it doesn't cover all the new features for C99, I think it is at least a start for people who are not familiar to C99 like me.

Learning x86 Calling Conventions by Examples

The x86 architecture features many different calling conventions. There are three major calling conventions in use: __cdecl, __stdcall, and __fastcall. We are going to force the compiler to generate assembly with different calling conventions in order to see how they work.

Understand Weak Symbols by Examples

Wikipedia defines the weak symbols: "In computing, a weak symbol is a symbol definition in an object file or dynamic library that may be overridden by other symbol definitions, its value will be zero if no definition found by loader." In other words, we can define a symbol that doesn't need to be resolved at link time. It is a very well-known feature and used a lot in Linux Kernel, Glibc, and so on.

Debian Backporting

It is easy to install packages on Debian. All you have to do is "apt-get install package". But what if we would like to install a newer version package? For example, git-core version on Debian stable is 1.4.4. It is too old and does not have basic commands such as git config, init,... etc. We may install git from Debian Backports. It is a easier way than building from source for most people.