Why globals shouldn't be initialized at 0 / NULL / false in the linux kernel?

Question

I'm using the checkpatch.pl script from the linux kernel for my own firmware since I use the same coding style (which I like).

There is just an error that I don't quite understand about global variables:

do not initialise globals to 0

For sure I want to avoid using globals as much as possible, but don't know why this is a style error?

Is it because some compilers don't put such globals in .BSS? (Usually they are smart enough)

Answer 1

First, it is redundant, and increases the size of the kernel (not what is finally loaded, but by having explicit instructions to the linker which are unnecessary).

It is part of a larger problem: Supposing that you had two different object files to link together, with different ideas of how to initialize them. Then the linker has to detect that and produce a symbol conflict error. The script is concerned with that as well.

Further reading:

• .bss vs COMMON: what goes where?
• Uninitialised global data in C – .bss section vs common symbols
• Shared Libraries Redux (Ian Lance Taylor)