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questions/answers/078.md

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+
+# Question 78
+
+
+What are the compilation stages?
+
+
+# Answer
+
+
+
+
+Preprocessing, translation, linking
+
+
+
+
+[prev](077.md) +++ [next](079.md)

questions/answers/079.md

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+
+# Question 79
+
+
+What is preprocessing?
+
+
+# Answer
+
+
+
+Performing (usually) textual substitution in program source code to 
+produce a modified source in the same language. The substitutions are 
+controlled via preprocessor flags (such as `-D`) and preprocessor directives
+such as `%define` or `%macro`.
+
+
+[prev](078.md) +++ [next](080.md)

questions/answers/080.md

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+
+# Question 80
+
+
+What is a macro instantiation?
+
+
+# Answer
+
+
+
+
+When a macro name occurs in program source, it gets substituted with its body.
+The macro body  with macro parameters substituted is called macro instantiation.
+
+
+
+[prev](079.md) +++ [next](081.md)

questions/answers/081.md

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+
+# Question 81
+
+ What is the `%define` directive?
+
+
+# Answer
+
+
+
+`%define` defines a preprocessor substitution.
+
+For example:
+
+```asm
+%define hello "Greetings, commander"
+
+db hello, 0  ; gets substituted with: db "Greetings, commander", 0 
+```
+
+The substitutions occur _before_ code generation.
+
+
+
+[prev](080.md) +++ [next](082.md)

questions/answers/082.md

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+
+# Question 82
+
+
+What is the `%macro` directive?
+
+
+# Answer
+
+
+
+
+```macro` directive allows you to define macros whose body spans over multiple 
+lines.
+
+For example:
+
+```asm
+%macro hello 2
+dq %1
+dq %2
+%endmacro          
+
+; Instantiation:
+
+hello 42,1337
+
+; substituted for:
+; dq 42
+; dq 1337
+```
+
+
+[prev](081.md) +++ [next](083.md)

questions/answers/086.md

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+
+# Question 86
+
+
+What are the three types of ELF object files?
+
+
+# Answer
+
+
+
+Relocatable object files, shared object files (dynamic libraries) and
+executable files.  
+
+
+[prev](085.md) +++ [next](087.md)

questions/answers/087.md

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+
+# Question 87
+
+
+What kind of headers are present in an ELF file?
+
+
+# Answer
+
+
+
+* File header (`readelf -f`)
+* Program headers (`readelf -h`)
+* Section headers (`readelf -S`)
+
+
+[prev](086.md) +++ [next](088.md)

questions/answers/088.md

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+
+# Question 88
+
+
+What is relocation?
+
+
+# Answer
+
+
+
+__Relocation__ is a process of assigning definitive addresses to various program parts
+and changing the program code the way all links are attributed correctly. We are
+speaking about all kinds of memory accesses by absolute addresses. Relocation is
+needed, for example, when the program consists of multiple modules, which are
+referencing one another. The order in which they will be placed in memory is not
+yet fixed, so the absolute addresses are not determined.
+
+
+[prev](087.md) +++ [next](089.md)

questions/answers/089.md

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+
+# Question 89
+
+
+What sections can be present in ELF files?
+
+
+# Answer
+
+
+
+* __.text__ stores machine instructions.
+* __.rodata__ stores read only data.
+* __.data__ stores initialized global variables.
+* __.bss__ stores readable and writable global variables, initialized to zero. There is no need to dump their contents into an object file as they are all filled with zeros anyway. Instead, a total section size is stored. An operating system may know faster ways of initializing such memory than zeroing it manually.  In assembly, you can put data here by placing `resb`, `resw`, and similar directives after the section __.bss__.
+* __.rel.text__ stores relocation table for the .text section. It is used to memorize places where a linker should modify .text after choosing the loading address for this specific object file.
+* __.rel.data_ stores a relocation table for data referenced in module.
+* __.debug__ stores a symbol table used to debug program. If the program was written in C or C++, it will store information not only about global variables (as __.symtab__ does) but also about local variables.
+* __.line__ defines correspondence with pieces of code and line numbers in source code. We need it because the correspondence between lines of source code in higher-level languages and assembly instructions is not
+straightforward. This information allows one to debug a program in a higher-level language line by line.
+* __.strtab__ stores character strings. It is like an array of strings. Other sections, such, as __.symtab__ and __.debug__,
+ use not immediate strings but their indices in __.strtab__.
+* __.symtab__ stores a symbol table. Whenever a programmer defines a label, NASM will create a symbol for it. 
+
+
+[prev](088.md) +++ [next](090.md)