\(3.2.\)Program Encoding

1.Program execution process

  Say we want to compile two C program p1.c and p2.c, we input the command:

linux> gcc -0g -o p p1.c p2.c

1. The C preprocessor expands the source code to include any files specified with #include commands and with #define declarations.

2. Compiler generates assembly code having name p1.s and p2.s.

3. Assembler converts the assembly code into binary object-code files p1.o and p2.o.

The object code contains binary representations of all instructions, but doesn't include the address of the global value.

4. Linker merges these two object-code files along with code implementing library functions (e.g., printf) and generates the final executable code file p(specified by -o p).

2.Machine code

  \(a.\)Program memory

  The program memory contains:

• the executable machine code for the program

• some information required by the operating system

• a run-time stack for managing procedure calls and returns

• blocks of memory allocated by the user (e.g., by using the malloc library function).

  \(b.\)Some command

  We use -S to see the assembly code generated by the compiler:

gcc -0g -S mstore.c

  We use -c to both compile and assemble the code:

gcc -0g -c mstore.c

  This will generate an object-code file mstore.o.

  To inspect the contents of machine-code, we can use the disassembler. The program objdump can serve the role:

objdump -d mstore.o

  The result is as below: