October 2018
Beginner
794 pages
19h 23m
English
Content preview from Hands-On System Programming with Linux
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Text segment
Text is code: the actual opcodes and operands that make up the machine instructions that are fed to the CPU to consume. Readers may recall the objdump --source ./hello_dbg we did in Chapter 1, Linux System Architecture, showing C code translated into assembly and machine language. This machine code resides within the process VAS in a segment called text. For example, let's say a program has 32 KB of text; when we run it, it becomes a process and the text segment takes 32 KB of virtual memory; that's 32K/4K = 8 (virtual) pages.
For optimization and protection, the OS marks, that is, protects, all these eight pages of text as read-execute (r-x). This makes sense: code will be read from memory and executed by the CPU, not written ...
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