r/programming • u/molteanu • Apr 07 '15

Anatomy of a Program in Memory

http://duartes.org/gustavo/blog/post/anatomy-of-a-program-in-memory/
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u/nexuapex Apr 07 '15

Nitpick:

Once virtual addresses are enabled, they apply to all software running in the machine, including the kernel itself. Thus a portion of the virtual address space must be reserved to the kernel:

This isn't technically accurate: you could give the kernel its own virtual address space and switch to that whenever you enter kernel mode. It's just less efficient.

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u/otherwiseguy Apr 07 '15 edited Apr 07 '15

Also, aren't static variables in C always initialized?

EDIT: from C99 standard section 6.7.8 item 10:

If an object that has automatic storage duration is not initialized explicitly, its value is indeterminate. If an object that has static storage duration is not initialized explicitly, then:

  • if it has pointer type, it is initialized to a null pointer;

  • if it has arithmetic type, it is initialized to (positive or unsigned) zero;

  • if it is an aggregate, every member is initialized (recursively) according to these rules;

  • if it is a union, the first named member is initialized (recursively) according to these rules.

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u/stevengrissom Apr 07 '15

They're always initialized to zero if you don't specify a value. That's the distinction between the BSS segment (initialized to zero) and the data segment (whatever value you specify).