I don't understand segmentation

[flyboy216]

So I'm reading about segmentation for x86, but I'm confused. If I understand correctly, each process is allowed 3 GB of total memory -- including code, stack, and heap:

LinuxDevCenter.com -- When Linux Runs Out of Memory

On the other hand, it sounds like Linux also uses _USER_CS and _USER_DS segment descriptors:

Section 2.3.* Segmentation in Linux

That makes it sound like the code and data segments *each* have 2^32 bytes of memory. For example:

"As an example, when the kernel invokes a function, it executes a call assembly language instruction specifying just the Offset component of its logical address; the Segment Selector is implicitly selected as the one referred to by the cs register."

Why should it need to use a segment selector if the code resides in the same 32-bit address space as the data?

Thanks!

[gerard4143]

Welcome to the forums!

I personally think these books on the kernel are good:

O'Reilly Media | Understanding the Linux Kernel

O'Reilly Media | Linux Kernel in a Nutshell

Also, look here for additional kernel information:

The Linux Kernel: The Book

Have fun with Linux!
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oz

New Users: * FAQ *

Note O'Reilly Media | Understanding the Linux Kernel has a section on linux segmentation
that may shed some light on your question...Gerard