Cse 322 Programming Languages and Compilers Lecture 16

Cse 322, Programming Languages and Compilers Lecture #16, May 24, 2007 • Runtime. c • Running the code • debugging assembler • division • strings for println • making test files 6/16/2021 1

Cse 322, Programming Languages and Compilers Project #3 • project #3 is due Thursday, June 7, 2007 at 5: 00 PM – this is in 14 days. – In order to get the course graded, there will be no extensions • Final exam will be Monday June 11 • Possibility – Tuesday June 5, limited lecture, and I answer questions in class about the project. 6/16/2021 2

Cse 322, Programming Languages and Compilers Runtime. c #include <stdio. h> extern int Mini_main(char* s); int main() { printf("Entering main in mini. Java programn"); Mini_main("123"); return 0; } void pr. String(char* s) { printf(s); printf("n"); } void pr. Int(int n) { printf("%dn", n); } 6/16/2021 3

Cse 322, Programming Languages and Compilers Assumptions • The first assumption is that the only visible name in the assembly code is Mini_main • runtime functions are in runtime. c – e. g. pr. Int and pr. String – these can be accessed as _pr. Int and _pr. String in assembly – E. g. pushl call addl 6/16/2021 underscore before the name of the C function %eax _pr. Int # pr. Int((MEM(V 4) / 2)) $4, %esp 4

Cse 322, Programming Languages and Compilers Running the code. • The compiler will write a file in assembly format. • The driver I supply will have a function that given a file name and a (IA 32 list) will format the instructions and print them to the file. – E. g. IA 32. print. Ia 32 "work/obj. s" x 86 • You should write the file into the same directory where runtime. c is • Then you should use gcc to compile – gcc runtime. c obj. s • Then you should run the program –. /a. exe 6/16/2021 5

Cse 322, Programming Languages and Compilers What if something goes wrong? • If you have the println working in mini. Java you can put in println to see where you are before it goes wrong. – So you may want to get this working first! (hint, Hint !!! ) • You can manually inspect the code, by looking at the generated file. Of course a good translator will put comments in the file appropriately. • You can try and run the code in a debugger. 6/16/2021 6

Cse 322, Programming Languages and Compilers Debugging Assembly • • • In order to get things correct you may want to debug assembly. I have successfully used the gdb debugger Resources – The web page http: //www. csee. umbc. edu/~cpatel 2/links/310/nasm/gdb_help. shtml was very helpful to me • Under Linux, and Cygwin on Windows, the complete documentation for gdb is available on the Linux system using the "info" command: – info gdb 6/16/2021 7

Cse 322, Programming Languages and Compilers Over all view • To debug • Compile with the –g option – gcc –g runtime. c obj. s • Then start the executable with the debugger – gdb a. exe • Inside the debugger run the code 6/16/2021 8

Cse 322, Programming Languages and Compilers Accessing variables • Variables in the assembly code have _x • but in the debugger the _ is not used • Registers are $eax $ebx $esp etc 6/16/2021 9

Cse 322, Programming Languages and Compilers Running code • start • step (s) – 1 step (either C or assembly) – goes into function calls • next (n) – 1 step (either C or assembly) – goes over function calls 6/16/2021 10

Cse 322, Programming Languages and Compilers Break commands • break Mini_main • break 12 – break at line 12, useful when in the C code 6/16/2021 11

Cse 322, Programming Languages and Compilers Printing things • print takes a format • print/d x • print/x temp – – – – – 6/16/2021 o(octal), x(hex), d(decimal), u(unsigned decimal), t(binary), f(float), a(address), i(instruction), c(char) and s(string). 12

Cse 322, Programming Languages and Compilers X examining things • x/count-format-size object • x/4 dw temp – print temp and the next 3 things of word size in decimal format • This is useful for examining the stack • x/8 dw $esp – print the top 8 words of the stack – works because the stack grows downwards 6/16/2021 13

Cse 322, Programming Languages and Compilers info (gdb) info reg eax ecx edx ebx esp ebp esi edi eip eflags cs ss ds es fs gs 6/16/2021 0 x 401075 4198517 0 x 0 0 0 x 4 c 76 0 x 4 4 0 x 22 ee 50 0 x 22 ee 68 0 x 4621 ac 4596140 0 x 61102 c 1 c 1628449820 0 x 401075 0 x 206 518 0 x 1 b 27 0 x 23 35 0 x 38 56 0 x 0 0 14

Cse 322, Programming Languages and Compilers Handling division • Division is tricky because you must have things in the correct registers. • to execute (x / y) • get x into %eax • clear %edx -- as long as x is positive – movl $0, %edx • get y into %ebx • Do the divide – idivl %ebx • Divides (%edx: %eax) as a 64 bit by %ebx – result in %eax – remainder in %edx 6/16/2021 15

Cse 322, Programming Languages and Compilers Handling strings for println • We need to allocate strings at the beginning of the assembly file. S_4: S_3: S_2: S_1: S_0: 6/16/2021 . text. asciz. globl "a && b = 0" "y/2 = 2" "y*z = 12" "y-z = 1" "x+y = 4" _Mini_main 16

Cse 322, Programming Languages and Compilers ML algorithm val string. Count = ref 0; val strings = ref ([]: IA 32 list) fun new. String s = let val n = !string. Count val _ = string. Count : = n+1 val label = "S_"^Int. to. String n in strings : = (Asciz(label, s, “literal") ): : (! strings); label end; 6/16/2021 17

Cse 322, Programming Languages and Compilers Translating fun compile. E exp = case exp of STRING(s) => let val label = new. String s in [ movl (Lit label, % eax) ] end 6/16/2021 18

Cse 322, Programming Languages and Compilers Collecting fun compile. Program xs = let val _ = string. Count : = 0 val _ = strings : = [] val body = List. concat (map compile. Func xs) in [ text() ] @ !strings @ body end; 6/16/2021 19

Cse 322, Programming Languages and Compilers Testing your compiler • The strategy to test your compiler is to build small minijava files that exercise 1 feature. • Then – – 6/16/2021 compile observe translation run through gcc run test file. 20

Cse 322, Programming Languages and Compilers My first mini. Java program class test 01 { public static void main(String[] a) { System. out. println("TEST 01"); System. out. println(123); System. out. println(true); } } 6/16/2021 21

Cse 322, Programming Languages and Compilers Testing arithmetic class test 01 { public static void main(String[] a) { int x = 0; int y = 4; int z = 3; boolean a = true; boolean b = false; System. out. println("x+y = 4"); System. out. println(x+y); System. out. println("y-z = 1"); System. out. println(y-z); System. out. println("y*z = 12"); System. out. println(y*z); System. out. println("y/2 = 2"); System. out. println(y/2); System. out. println("a && b = 0"); System. out. println(a && b); } } 6/16/2021 22

Cse 322, Programming Languages and Compilers http: //www. cygwin. com/ 6/16/2021 23