1 // 2 // A recursive function demo 3 // 4 5 /* -------------------------------------------------- 6 Define required labels for EGTAPI 7 -------------------------------------------------- */ 8 .global main, Stop, CodeEnd, DataStart, DataEnd 9 .global f, result 10 11 /* -------------------------------------------------- 12 Begin of the program instructions 13 -------------------------------------------------- */ 14 .text 15 main: 16 17 // result = f(2,4) 18 19 /* ------------------------------------------------- 20 Pass parameters (using stack) 21 ------------------------------------------------- */ 22 0000 0400A0E3 mov r0, #4 23 0004 04002DE5 push {r0} // Pass param 2 (=4) 24 0008 0200A0E3 mov r0, #2 25 000c 04002DE5 push {r0} // Pass param 1 (=2) 26 27 /* ---------------------------------------------------------------- 28 call result = f(2,4) 29 ---------------------------------------------------------------- */ 30 0010 FEFFFFEB bl f 31 0014 08D08DE2 add sp, sp, #8 // Clean up the parameters 32 33 /* ----------------------------------------------------------------- 34 Save return value (in r0) to variable result 35 ----------------------------------------------------------------- */ 36 0018 001000E3 movw r1, #:lower16:result // Do NOT use r0 !!! 37 001c 001040E3 movt r1, #:upper16:result // (Because r0 contains the return value) 38 39 0020 000081E5 str r0, [r1] // This will store return value in sum 40 41 Stop: 42 0024 0000A0E1 nop // Stop point of main( ) 43 44 45 46 47 48 /* ---------------------------------------------------------------- 49 Function int f(int a, int b) 50 51 Stack frame structure: 52 53 i -8 54 s -4 55 old FP <--------------------------------- FP 56 old LR (ret addr) 57 a +8 58 b +12 59 60 Body of f(a,b) 61 62 s = 0; 63 for (i = a; i < b; i++) 64 s = s + f(a+1, b-1) + 1; 65 return s; 66 ---------------------------------------------------------------- */ 67 68 f: 69 70 // When f begins, we will have: a,b on the stack 71 72 /* ========================================================== 73 Function Prelude: complete the stack frame structure 74 ========================================================== */ 75 0028 04E02DE5 push {lr} // Save LR (return address) 76 002c 04B02DE5 push {fp} // Save FP (used by caller) 77 0030 0DB0A0E1 mov fp, sp // Mark the stack top location before 78 // allocating any local variables 79 0034 08D04DE2 sub sp, sp, #8 // Allocate 2 int variables on the stack 80 81 /* =============================================== 82 We completed the stack frame 83 Now we can write the function body 84 =============================================== */ 85 // s = 0 86 0038 0000A0E3 mov r0, #0 87 003c 04000BE5 str r0, [fp, #-4] // assign 0 to s 88 89 // i = a 90 0040 08009BE5 ldr r0, [fp, #8] // r0 = a 91 0044 08000BE5 str r0, [fp, #-8] // assign to i 92 93 while: 94 // while ( i < b ) 95 0048 08001BE5 ldr r0, [fp, #-8] // r0 = i 96 004c 0C109BE5 ldr r1, [fp, #12] // r1 = b 97 98 0050 010050E1 cmp r0, r1 // i ? b 99 0054 0F0000AA bge whileEnd // Exit for loop 100 101 // We CANNOT compute s + f(a+1, b-1) + 1 without the 102 // value (= a number) for: f(a+1, b-1) 103 104 // Compute f(a+1, b-1) first ! 105 0058 0C009BE5 ldr r0, [fp, #12] // r0 = b 106 005c 010040E2 sub r0, r0, #1 // r0 = b-1 107 0060 04002DE5 push {r0} // pass param2 (b-1) 108 109 0064 08009BE5 ldr r0, [fp, #8] // r0 = a 110 0068 010080E2 add r0, r0, #1 // r0 = a+1 111 006c 04002DE5 push {r0} // pass param1 (a+1) to f on stack 112 113 0070 FEFFFFEB bl f 114 0074 08D08DE2 add sp, sp, #8 // Clean up parameter (n-1) from stack 115 116 // We can now compute s + f(a+1, b-1) + 1 117 118 0078 04101BE5 ldr r1, [fp, #-4] // r1 = s 119 007c 010080E0 add r0, r0, r1 // r0 = s + f(a+1, b-1) 120 0080 010080E2 add r0, r0, #1 // r0 = s + f(a+1, b-1) + 1 121 122 0084 04000BE5 str r0, [fp, #-4] // Assign s + f(a+1, b-1) + 1 to s 123 124 // i++ 125 0088 08001BE5 ldr r0, [fp, #-8] // r0 = i 126 008c 010080E2 add r0, r0, #1 // r0 = i + 1 127 0090 08000BE5 str r0, [fp, #-8] // Assign i+1 to i 128 129 0094 EBFFFFEA b while 130 131 whileEnd: 132 133 // return s in r0 134 0098 04001BE5 ldr r0, [fp, #-4] // r0 = s 135 136 /* ============================================================= 137 Function Postlude: de-allocate local variable and restore FP 138 ============================================================= */ 139 009c 0BD0A0E1 mov sp, fp // De-allocate local variables 140 00a0 04B09DE4 pop {fp} // Restore fp 141 00a4 04F09DE4 pop {pc} // Return to the caller 142 143 144 145 146 CodeEnd: 147 00a8 0000A0E1 nop 148 149 /* -------------------------------------------------- 150 Begin of the permanent program variables 151 -------------------------------------------------- */ 152 .data 153 DataStart: 154 155 0000 00000000 result: .skip 4 156 157 DataEnd: 158 159 .end DEFINED SYMBOLS /home/cs255001/cs255/demo/8-sub/recurse.s:15 .text:0000000000000000 main /home/cs255001/cs255/demo/8-sub/recurse.s:41 .text:0000000000000024 Stop /home/cs255001/cs255/demo/8-sub/recurse.s:146 .text:00000000000000a8 CodeEnd /home/cs255001/cs255/demo/8-sub/recurse.s:153 .data:0000000000000000 DataStart /home/cs255001/cs255/demo/8-sub/recurse.s:157 .data:0000000000000004 DataEnd /home/cs255001/cs255/demo/8-sub/recurse.s:68 .text:0000000000000028 f /home/cs255001/cs255/demo/8-sub/recurse.s:155 .data:0000000000000000 result /home/cs255001/cs255/demo/8-sub/recurse.s:22 .text:0000000000000000 $a /home/cs255001/cs255/demo/8-sub/recurse.s:93 .text:0000000000000048 while /home/cs255001/cs255/demo/8-sub/recurse.s:131 .text:0000000000000098 whileEnd /home/cs255001/cs255/demo/8-sub/recurse.s:155 .data:0000000000000000 $d NO UNDEFINED SYMBOLS 1 2 .global malloc, print 3 .global stdout_start, stdout_end 4 5 // ********************************************** 6 // malloc: simulate memory allocate 7 // 8 // This function will NOT change ANY registers 9 // (I.e.: will preserve ALL registers) 10 // ********************************************** 11 malloc: 12 0000 0E002DE9 push {r1, r2, r3} // Save scratch registers 13 14 0004 001000E3 movw r1, #:lower16:maddr 15 0008 001040E3 movt r1, #:upper16:maddr // r1 = &maddr 16 000c 003091E5 ldr r3, [r1] // r3 = maddr 17 18 // -------------------------------------- 19 // Make new maddr (divisible by 8) 20 // -------------------------------------- 21 22 0010 002083E0 add r2, r3, r0 // New maddr 23 0014 082082E2 add r2, r2, #8 // Making sure it increase 24 25 0018 0700A0E3 mov r0, #0x7 // r0 = 0000..00111 26 001c 0000E0E1 mvn r0, r0 // r0 = 1111..11000 27 0020 002002E0 and r2, r2, r0 // Knock off the last 3 bits 28 0024 002081E5 str r2, [r1] // Update maddr 29 30 31 // -------------------------------------- 32 // Return to caller 33 // -------------------------------------- 34 0028 0300A0E1 mov r0, r3 // Return maddr value in r0 35 002c 0E00BDE8 pop {r1, r2, r3} // Restore scratch registers 36 0030 0EF0A0E1 mov pc, lr // Return 37 38 0034 00000400 maddr: .word 0x40000 // Start address of the heap 39 40 41 // ******************************************************************* 42 // print: simulate print output in Egtapi 43 // 44 // input: r0 = address of string 45 // r1 = # characters to write 46 // 47 // Egtapi will show ASCII data stored starting at stdout_start 48 // until stdout_end in its output area 49 // 50 // This function will NOT change ANY registers 51 // (I.e.: will preserve ALL registers) 52 // ******************************************************************* 53 print: 54 0038 1C002DE9 push {r2, r3, r4} // Save scratch registers 55 56 003c 002000E3 movw r2, #:lower16:stdout_end 57 0040 002040E3 movt r2, #:upper16:stdout_end // r2 = &stdout_end 58 0044 002092E5 ldr r2, [r2] // r2 = stdout_end 59 60 0048 0130A0E1 mov r3, r1 // r3 = # char to copy 61 62 printLoop: 63 004c 000053E3 cmp r3, #0 64 0050 0500000A beq printDone 65 66 0054 0040D0E5 ldrb r4, [r0] // Get next char 67 0058 0040C2E5 strb r4, [r2] // Write next char 68 69 005c 010080E2 add r0, r0, #1 70 0060 012082E2 add r2, r2, #1 71 72 0064 013043E2 sub r3, r3, #1 73 74 0068 F7FFFFEA b printLoop 75 76 printDone: 77 006c 2040A0E3 mov r4, #32 // Space 78 0070 0040C2E5 strb r4, [r2] 79 0074 012082E2 add r2, r2, #1 80 81 0078 003000E3 movw r3, #:lower16:stdout_end 82 007c 003040E3 movt r3, #:upper16:stdout_end // r2 = &stdout_end 83 0080 002083E5 str r2, [r3] 84 85 0084 1C00BDE8 pop {r2, r3, r4} // Restore scratch registers 86 0088 0EF0A0E1 mov pc, lr // Return 87 88 89 90 91 008c 00000500 stdout_start: .word 0x50000 // This value remains unchanged 92 0090 00000500 stdout_end: .word 0x50000 93 94 95 .end DEFINED SYMBOLS /home/egtapi/lib/cs255lib.s:11 .text:0000000000000000 malloc /home/egtapi/lib/cs255lib.s:53 .text:0000000000000038 print /home/egtapi/lib/cs255lib.s:91 .text:000000000000008c stdout_start /home/egtapi/lib/cs255lib.s:92 .text:0000000000000090 stdout_end /home/egtapi/lib/cs255lib.s:12 .text:0000000000000000 $a /home/egtapi/lib/cs255lib.s:38 .text:0000000000000034 maddr /home/egtapi/lib/cs255lib.s:38 .text:0000000000000034 $d /home/egtapi/lib/cs255lib.s:54 .text:0000000000000038 $a /home/egtapi/lib/cs255lib.s:62 .text:000000000000004c printLoop /home/egtapi/lib/cs255lib.s:76 .text:000000000000006c printDone /home/egtapi/lib/cs255lib.s:91 .text:000000000000008c $d NO UNDEFINED SYMBOLS