1.GCC related introduction
What is the difference between GCC and gcc?
â— GCC (GNU Compiler Collection)
GNU compiler collection, compilers for many languages: C, C++, Java, D, Objective-C, etc
â— gcc: specifically refers to the C compiler in GCC
GCC VS embedded
â— Most embedded operating systems are based on GCC for source code compilation.
Linux, VxWorks, Android, etc
â—Application in actual development
Kernel development: gcc
Application development: gcc / g++ / gdc
2 first known compiler
The process of gcc compiling code into an executable program completes four steps of preprocessing, compilation, assembly, and linking.
The compiler consists of a preprocessor (cpp tool, C Preprocessor), a compiler (cc tool, C and C++ compiler), an assembler (as tool, assembler), and a connector (ld tool).
3 gcc key compilation options
3.1 Preprocessing instructions
3.1.1 Instruction format
Gcc -E file.c -o file.i
3.1.2 Preprocessing file related content
From the file.i file we can see that there are a large number of lines starting with "#". The format of each line is "# line number file name flag", where "line number" and "file name" indicate which line of the file from which the content starting from the next line comes from; the flag can be 1, 2, 3 And 4 four numbers, the meaning of each number is as follows:
When file.c uses non-system header files and they are not in the current directory, they need to be specified by using gcc's -I parameter, otherwise gcc will report an error because it cannot obtain the necessary header files for macro expansion.
3.2 Compilation instructions
3.2.1 Instruction format
Gcc -S file.i -o file.s gcc -S -O2 file.c -o file.s
3.2.2 Description
When using the -S parameter, we can use the -O option as needed.
3.3 assembly instructions
3.3.1 Instruction format
Gcc -c file.s -o file.o
3.4 Generating a mapping file
3.4.1 Instruction format
Gcc -Wl,-Map=file.map file.c
3.4.2 Description
The mapping file is generated by the ld linker. We can use the mapping file to understand the layout information of each symbol in memory in a program file. Gcc's -Wl option is used to specify the options passed to the linker. The -Map=file.map option is passed by gcc to the linker to instruct the linker to generate a map file named file.map for us. When using the -Wl option, if there are multiple options behind it, you need to split it with a comma.
3.5 macro definition
3.5.1 Instruction format
Gcc -D'TEST="test"' file.c
3.5.2 Description
If the macro is a string, it needs to be enclosed in single quotes.
3.6 Obtaining the System Header Path
3.6.1 Instruction format
Gcc -v file.c
3.6.2 Description
The system header file refers to the C language itself and the operating system related header files. When using the -v option to get the system header file path, you must bring a valid C program source file, otherwise the information output by gcc will not contain the system header file path.
3.7 Generating dependencies
3.7.1 Instruction format
Get the full dependency of the target: gcc -M test.c Get the partial dependencies of the target: gcc -MM test.c
3.7.2 Description
Since the system header files are not changed in most cases, it is not necessary to include them in constructing the dependencies required by make. With the -MM option, you can have gcc generate dependencies that do not contain system header files.
3.8 Specifying the library file and library file search path
3.8.1 Instruction format
-L option: Specify the search path of the library file -l option: specify the library file ar crs libfunc.a func.o gcc test.c -L. -lfunc
3.8.2 Description
Note that the -L option tells gcc which directory to look up the library file from, and can use it multiple times to specify multiple directories; the -I option tells gcc which library name to link to when generating the executable. Options can also be used multiple times to specify multiple libraries. When using the -l option, be aware that the names that follow are not including the "lib" prefix and the ".a" suffix.
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