{small lecturenumber - hepage :} Stages of Compilation{small lecturenumber - hepage :} Stages of Compilation{small lecturenumber - hepage :} Example{small lecturenumber - hepage :} Stages of Compilation{small lecturenumber - hepage :} Included headers{small lecturenumber - hepage :} Macros{small lecturenumber - hepage :} Defining constants{small lecturenumber - hepage :} Macros{small lecturenumber - hepage :} Macros{small lecturenumber - hepage :} The Symbol table{small lecturenumber - hepage :} GDB{small lecturenumber - hepage :} GDB{small lecturenumber - hepage :} GDB{small lecturenumber - hepage :} GDBIntro to Programming IICompiling and debuggingChris BrooksDepartment of Computer ScienceUniversity of San FranciscoDepartment of Computer Science — University of San Francisco – p. 1/??24-2: Stages of Compilation•What are the stages of the compilation of a program?Department of Computer Science — University of San Francisco – p. 2/??24-3: Stages of Compilation•What are the stages of the compilation of a program?•Lexing - separate source code into tokens.•Parsing - evaluate statements and generate assembly code•Assembly - transform assembly code into binary code.•Linking - Multiple object files are merged into a singleexecutable.Department of Computer Science — University of San Francisco – p. 3/??24-4: Example•Assume we start with two source files: file1.c and file2.c•First, each file is parsed and compiled separately.•The linker then builds a single executable◦Resolves all function calls and variable references to asingle address space.◦Builds an executable with a single “main” entry point.Department of Computer Science — University of San Francisco – p. 4/??24-5: Stages of Compilation•The C compiler adds another step at the beginning of theprocess.•This step is called preprocessing.•The preprocessor does three things:◦Strips out comments.◦“Pastes in” included headers.◦Expands macros.Department of Computer Science — University of San Francisco – p. 5/??24-6: Included headers•In C, headers are included directly in the source code at thevery first stage of compilation.•This can sometimes lead to strange compiler errors.◦File A includes file B, and file B includes file A.Department of Computer Science — University of San Francisco – p. 6/??24-7: Macros•The C preprocessor also uses a #define directive.•This is used to:◦Define constants◦Define macros: small chunks of code.Department of Computer Science — University of San Francisco – p. 7/??24-8: Defining constants#define ARRAYSIZE 100int arr[ARRAYSIZE];•The preprocessor replaces ARRAYSIZE with 100•Note: this is NOT a variable - the preprocessor just replaces thestring ’ARRAYSIZE’ with the string ’100’Department of Computer Science — University of San Francisco – p. 8/??24-9: Macros•We can also do this syntactic replacement with blocks of code.#define SWAP(a,b) {int temp = a; a = b; b = temp;}int main(void) {int x = 10;int y = 20;printf("%d %d", x,y);SWAP(x,y);printf("%d %d", x,y);}•All occurrences of SWAP are replaced with the correspondingcode.Department of Computer Science — University of San Francisco – p. 9/??24-10: Macros•Note that SWAP is not a function.◦Code is just cut-and-pasted.◦No checking of argument types◦No return types•Advantages: useful for ’quick and dirty’ operations, no overheadfrom a function call.•Disadvantages: Can be difficult to debug.Department of Computer Science — University of San Francisco – p. 10/??24-11: The Symbol table•Normally, gcc constructs a symbol table during the compilationprocess.•This is used to map variable names to addresses.•Typically, the symbol table is discarded after object files aregenerated.•Compiling with the -g option retains the symbol table.•This allows us to run the debugger.Department of Computer Science — University of San Francisco – p. 11/??24-12: GDB•GDB is the GNU debugger.•This is very helpful for debugging C programs.•Same features as the eclipse debugger.◦Break, run, list, print variables, step.Department of Computer Science — University of San Francisco – p. 12/??24-13: GDB•break - stop at:◦a particular line◦a particular function.Department of Computer Science — University of San Francisco – p. 13/??24-14: GDB•run - start a program•continue - continue execution from the breakpoint.•step - move to the next line of the programDepartment of Computer Science — University of San Francisco – p. 14/??24-15: GDB•print - show the current value of a variable•list - show the current lines in the program.Department of Computer Science — University of San Francisco – p.
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