1 /* -------------------------------------------------------------- 2 Show how the program stack "magically" handles 3 multiple functions that store parameters and local variables 4 on program stack 5 -------------------------------------------------------------- */ 6 7 .global main, Stop, CodeEnd, DataStart, DataEnd 8 9 .global f, k 10 11 /* -------------------------------------------------- 12 Begin of the program instructions 13 -------------------------------------------------- */ 14 .text 15 main: 16 17 /* ========================================= 18 Pass k to f( ) by value 19 ========================================= */ 20 0000 000000E3 movw r0, #:lower16:k 21 0004 000040E3 movt r0, #:upper16:k // r0 = address of k 22 0008 000090E5 ldr r0, [r0] // r0 = value of k 23 000c 04002DE5 push {r0} // Pass k by value (pass k's value) 24 25 0010 FEFFFFEB bl f // Call function f 26 0014 04D08DE2 add sp, sp, #4 // Clean up parameters on the stack 27 28 0018 0000A0E1 nop 29 001c 0000A0E1 nop 30 31 Stop: 32 0020 0000A0E1 nop 33 34 35 /* ================================================ 36 Function f that gets a parameter by value 37 38 Stack frame of f( ): 39 40 FP--> +-----------+ 41 | old FP | FP + 0 42 +-----------+ 43 | ret addr | FP + 4 44 +-----------+ 45 | param a | FP + 8 46 +-----------+ 47 ================================================ */ 48 f: 49 /* **************************************** 50 Prelude: build stack frame 51 **************************************** */ 52 0024 04E02DE5 push {lr} // Save return address in LR 53 0028 04B02DE5 push {fp} // Save Frame Pointer in FP 54 002c 0DB0A0E1 mov fp, sp // Initialize my own FP 55 0030 00D04DE2 sub sp, sp, #0 // I create 0 local variable in stack 56 57 /* ======================================= 58 a = a + 1 59 ======================================= */ 60 0034 08009BE5 ldr r0, [fp, #8] // r0 = a 61 0038 010080E2 add r0, r0, #1 // r0 = a + 1 62 003c 08008BE5 str r0, [fp, #8] // a = a + 1 63 64 65 /* ************************************************ 66 Postlude: break down stack frame 67 ************************************************ */ 68 0040 0BD0A0E1 mov sp, fp // De-allocate the local variables 69 0044 04B09DE4 pop {fp} // Restore old FP 70 71 0048 04F09DE4 pop {pc} // Return 72 73 74 75 76 CodeEnd: 77 004c 0000A0E1 nop 78 79 /* -------------------------------------------------- 80 Begin of the permanent program variables 81 -------------------------------------------------- */ 82 .data 83 DataStart: 84 85 0000 07000000 k: .4byte 7 86 87 DataEnd: 88 89 .end DEFINED SYMBOLS /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:15 .text:0000000000000000 main /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:31 .text:0000000000000020 Stop /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:76 .text:000000000000004c CodeEnd /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:83 .data:0000000000000000 DataStart /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:87 .data:0000000000000004 DataEnd /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:48 .text:0000000000000024 f /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:85 .data:0000000000000000 k /home/cs255001/cs255/demo/A-pass-by-ref/pass-by-value.s:20 .text:0000000000000000 $a 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