1 // 2 // Illustrate problem when you use registers to store important values 3 // and call another method 4 // 5 /* -------------------------------------------------- 6 Define required labels for EGTAPI 7 -------------------------------------------------- */ 8 .global main, Stop, CodeEnd, DataStart, DataEnd 9 .global square 10 11 /* -------------------------------------------------- 12 Begin of the program instructions 13 -------------------------------------------------- */ 14 .text 15 main: 16 // ********************************************* 17 // Test (1): result = square(3) 18 // Test (2): result = square(3) + square(4) 19 // ********************************************* 20 0000 0300A0E3 mov r0, #3 21 0004 FEFFFFEB bl square // r0 = 3*3 22 23 0008 0090A0E1 mov r9, r0 // Save result (r0) in reg r9 ????? 24 25 26 000c 0400A0E3 mov r0, #4 27 0010 FEFFFFEB bl square // r0 = 4*4 28 29 0014 000089E0 add r0, r9, r0 30 31 32 0018 001000E3 movw r1, #:lower16:result 33 001c 001040E3 movt r1, #:upper16:result 34 0020 000081E5 str r0, [r1] // Store result 35 36 37 38 Stop: 39 0024 0000A0E1 nop // Stop point of main( ) 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 /* ---------------------------------------------------------------- 57 Function square(x) 58 agreed inputs: r0 = x 59 agreed return: r0 = x*x 60 ---------------------------------------------------------------- */ 61 62 square: 63 0028 0010A0E1 mov r1, r0 64 002c 910000E0 mul r0, r1, r0 65 66 0030 0010A0E3 mov r1, #0 67 0034 0020A0E3 mov r2, #0 68 0038 0030A0E3 mov r3, #0 69 003c 0040A0E3 mov r4, #0 70 0040 0050A0E3 mov r5, #0 71 0044 0060A0E3 mov r6, #0 72 0048 0070A0E3 mov r7, #0 73 004c 0080A0E3 mov r8, #0 74 0050 0090A0E3 mov r9, #0 75 0054 00A0A0E3 mov r10, #0 76 77 0058 0EF0A0E1 mov pc, lr // Return to the caller 78 79 CodeEnd: 80 005c 0000A0E1 nop 81 82 /* -------------------------------------------------- 83 Begin of the permanent program variables 84 -------------------------------------------------- */ 85 .data 86 DataStart: 87 88 0000 00000000 result: .skip 4 89 90 DataEnd: 91 92 .end DEFINED SYMBOLS /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:15 .text:0000000000000000 main /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:38 .text:0000000000000024 Stop /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:79 .text:000000000000005c CodeEnd /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:86 .data:0000000000000000 DataStart /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:90 .data:0000000000000004 DataEnd /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:62 .text:0000000000000028 square /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:20 .text:0000000000000000 $a /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:88 .data:0000000000000000 result /home/cs255001/cs255/asm/8-sub/demo-overwrite-reg.s:88 .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