[compilation and assembly link] coff file and structure description

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COFF The document states

coff The file is essentially the file generated by the code in the compilation stage .

1. stay windows On the system , To be exact, use visual studio Generation time , Will produce obj file , It is generally stored in the same level of code Release or Debug Under the table of contents ;
2. stay linux Upper use gcc When compiling , The generated is out file .

So let's take a look at COFF The official definition of the document ：

COFF—— Common object file format （Common Object File Format）, Is a very popular object file format （ Be careful ： It is not said here that it is “ The goal is ” file , It is for and the target file generated by the compiler （.o/.obj） To distinguish , Because this format is not only used for target files , The library files 、 Executable files are often in this format ）. Use vs The generated object file （*.obj） This is the format . Other compilers , Such as GCC（GNU Compiler Collection）、ICL（Intel C/C++ Compiler）、VectorC, Target files in this format are also used . not only C/C++, Many other languages also use object files in this format

The object file of unified format brings great convenience to mixed language programming .

Of course , This is not the only object file format . Other common formats are OMF- Object model file （Object Module File） as well as ELF- Executable and connection file format （Executable and Linking Format）.OMF It's a large group IT Giant in n A format developed in , stay Windows Very common on the platform . What everyone likes Borland The target file used by the company now is in this format .MS and Intel stay n The same format was used years ago , Now they all switch to the opposite side , use COFF Format .ELF Format in non - Windows Used more on the platform , stay Windows I haven't seen the platform .

COFF File structure

COFF There is a total of 8 Species data , As shown in the following table , The paragraph header and paragraph data can have multiple sections . By default ,COFF File contains 3 Segments ：.text： Usually contains executable code ;.data： Usually contains initialized data ;.bss： Usually reserve space for uninitialized data .

among , The file header ~ The line number entry table is closely related to the loading file .

COFF File structure	explain	describe	Example
File header	The file header	For preservation COFF Basic information of the document , Such as document identification , The position of each table, etc , As shown on the right
Optional Header	Optional head	Similar to header , It's also used to save information , It mainly saves the information not described in the file header .
Section Header	Paragraph header	Used to describe paragraph information , Each paragraph has a paragraph header to describe , The number of paragraphs will be indicated in the header .
Section Header n
Section Data	Paragraph data	Paragraph data is usually COFF The largest data segment in the file , The real data of each paragraph is saved in this location , You can see the relevant information in the description at the beginning of the paragraph .
Relocation Directives	Relocation table	This table usually exists only in the target file , He used to describe COFF Relocation information of symbols in the file .
Line Numbers	Line number table
Symbol Table	The symbol table	For preservation COFF Information of all symbols used in the file , Link multiple COFF When you file , This table helps us reposition symbols . It is also used when debugging programs .	About Windows COFF Understanding of symbol table - Orange cub - Blog Garden
String Table	String table	Save string . Used to save some strings whose number of characters exceeds the maximum number of name arrays in the symbol table and de segment header .

In this paper, the reference

1. coff File analysis _zzljn The column _coff File parsing
2. Miao Jun , Ni Qizhi , MIAOJun, etc. . COFF Implementation and application of file analysis extractor [J]. Modern electronic technology , 2009, 32(2):4.
3. COFF File format _redleaves The column _coff

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