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A nasty string initialization bug in C

Today I encountered a bug that was quite difficult to find regarding strings. In order for strings to work they must be null-terminated, and this implies that an array of characters can contain a string with a length equal to the array size minus one, because there must be space for the null character. I found out that, when initializing array of chars with strings, the compiler does not complain if just the null character doesn’t fit.

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Hardware Environment for a BeagleBoard XM with JTAG

BeagleBoard XM

I recently decided to embark on writing my own C++ real-time operating system for embedded systems – I’ve so far made some progress using software emulation with QEMU but I feel it’s time to move on to real hardware. I’ve chosen to use the very popular BeagleBoard XM – mostly because it represents incredible value for money given but also due to it’s extensive user community.

This blog post provides an overview of the components required to get started with a BeagleBoard XM and JTAG emulator. I will also include my experience/rationale in selecting and buying the various components required (Board, JTAG Emulator, etc).

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PrintK Format Specifiers

As a kernel developer you’ll probably find yourself treating the ‘printk’ function as a drop-in replacement for the ‘printf’ function provided by any useful C library such as uclibc or glibc – After all, it’s usage is virtually the same. It was for this reason that I found my self naively surprised when reading the source for the kernel’s implementation – I was surprised because it offers many more features than the typical C libraries’ implementation. As I was unable to find any useful documentation on this – I thought I’d provide a brief overview.

Let’s start with the typical ‘%p’ type format specifier – we usually use it for printing the address of a pointer. However if you take a peek at the ‘pointer’ function in lib/vsprintf.c you’ll notice that you can further specify the pointer type to print additional information. We’ll look at some examples.

printk("%pf %pF\n", ptr, ptr) will print:
module_start module_start+0x0/0x62 [hello] 



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