System Programming

" One vision, one purpose. "

Chapter Three - Linux Programming

3.1 GCC

3.1.1 What is GCC

GCC is short for GNU Compiler Collection.

3.1.2 Compile Procedure

Write source code, e.g. main.c.

gcc -E main.c -o main.i: Preprocess, insert header files, macro replacement and remove comments.

gcc -S main.i -o main.s: C compiler complies C to assembly.

gcc -c main.s -o main.o: Assembler will compile assembly to binary file.

gcc main.o [trivia.o ...] -o main: Perform linkage to generate the final executable.

PS: It seems that GCC need file extension to identify file type. :P

3.1.3 Extra Compile Options

parameter meaning

-g add debug info, gdb needs this

-D add extra macro, e.g. -DDEBUG or -DDEBUG=0

-O -O1 -O2 -O3 optimization

-W1 -W2 -W3 -Wall warning level

-I extra include directory, e.g. -I inc or -Iinc to add ./inc

-L extra library directory, e.g. -L. or -L . to add ./

parameter	meaning
`-g`	add debug info, `gdb` needs this
`-D`	add extra macro, e.g. `-DDEBUG` or `-DDEBUG=0`
`-O` `-O1` `-O2` `-O3`	optimization
`-W1` `-W2` `-W3` `-Wall`	warning level
`-I`	extra include directory, e.g. `-I inc` or `-Iinc` to add `./inc`
`-L`	extra library directory, e.g. `-L.` or `-L .` to add `./`

3.1.4 Library

3.1.4.1 Static Library

Create static library. ar is for archive, huh?
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gcc -c tinyxml.c -o tinyxml.o
ar cr libtinyxml.a tinyxml.o
Use static library.
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gcc -o main main.o -L. -ltinyxml

3.1.4.1 Dynamic Library

Create dynamic library.
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gcc -shared -fPIC -c fmod.c -o fmod.o
gcc -shared -fPIC -o libfmod.so fmod.o
Use dynamic library. We have to set library path before we run the program. Or it won’t find it. Linux doesn’t support, you know, #pragma things. :(
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# Do the linkage.
gcc main.c libfmod.so -o main

# Set library path.
LD_LIBRARY_PATH=.
export LD_LIBRARY_PATH

# Run the executable.
./main
With dynamic library, if the dynamic library changes, it doesn’t need another compile, and the output will change accordingly.

3.2 GDB

“I don’t like nude GDB at all!”

3.2.1 Launch GDB

GDB can be launched with executable name.
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# Method 1
gdb main
# Method 2
gdb
file main

3.2.2 Run Program

Err… after you successfully launched GDB.
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run [...args]
start [..]		# will stops at main
continue		# continue running
Why bother doing this like a primitive and not using VS with WSL?

3.2.3 Break Point

Many ways to add break point using break, a.k.a. b.
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break [function name]
break [line number]
break [filename] : [line number]
break [*adress]

3.2.4 Watch

Ahh!!!

1	print variable

3.3 Make

3.3.1 Meet Make

make 是一个自动化的程序自动维护工具，它根据 Makefile 所描述的“依赖关系”自动决定项目的那些部分需要重新编译。

make 根据目录下的 Makefile 文件确定文件的依赖关系，并确定哪些需要重新生成或不生成。

make 将第一个目标文件作为最终目标文件，如果目标文件不存在，或目标文件递归依赖的目标有改动，则该目标文件需要重新生成。否则不需要生成。

.PHONY 表示其后的目标是伪目标，而不将其作为文件处理。

3.3.2 Makefile

The format of Makefile is as follows.

1 2	target: prerequisites <TAB>command

Here, I’d like to give an example.

# File structure
.
├── Makefile
├── include
│   ├── dylib.h
│   ├── fun1.h
│   └── fun2.h
├── lib
│   └── libdy.so
└── src
    ├── fun1.c
    ├── fun2.c
    └── main.c
# Makefile
main: init int/main.o int/fun1.o int/fun2.o lib/libdy.so
   	gcc int/main.o int/fun1.o int/fun2.o lib/libdy.so -o main -I include
   int/main.o: src/main.c
   	gcc -c src/main.c -o int/main.o -I include
   int/fun1.o: src/fun1.c include/fun1.h
   	gcc -c src/fun1.c -o int/fun1.o -I include
   int/fun2.o: src/fun2.c include/fun2.h
   	gcc -c src/fun2.c -o int/fun2.o -I include
   # This dynamic library doesn't have definition.
# lib/libdy.so:
.PHONY: init clean
init:
   	mkdir -p ./int
   clean:
   	rm -r ./int/