Question

Question 2 ARM Assembly Language (25 marks) An ARM instruction set summary is provided at the end of this paper. (5 marks) Explain the difference between eor and eors instruction. Use an example to show why both forms are useful. а. b. (5 marks) Explain using an example what the "Idr r3, [r7,#4]" instruction does. c. (10 marks) The following is the assembly language generated by a C compile type mystery, %function mystery: args 0, pretend = 0, frame = 8 @ frame_needed 1, uses anonymous_args = 0 @ link register save eliminated. push r7} sub - sp, sp, #12 r7, sp, #0 add r0, [r7, #4] str r1, [r7] Idr str r2, [r7] r3, [r7, #4] r2, гз Idr cmp it CS movcs r3, r2 гО, г3 adds r7, r7, #12 sp, r7 sp needed Idr r7, [sp], #4 Ir mov mov bx Annotate each line of the function with comments to explain what each line does. Write an equivalent C function and explain what it computes. d. (5 marks) Could the assembly language function above be executed using only the Thumb-2 instruction set? Explain how you arrived at your answer.

Answer 1

) D'fference bctucen eor & eons - iCal Exclusive OR T Perfoms Eo Eon means XoR oPeation. eons aso used to Perfosm hgical Enclusive R oPeration motouctions But Eon 1s Suppo ted by Contex-Mo that upolate te figgs S that S EORS Syntax £Rdj , RnRm EORS Rddestination aegi iSICT Kn holols tue fixst opaauel and is Same as Regiegen Rmholds tte g"d oPoraud. destinafion It o loads Hhe data n to 1g The Source is 91,e s în ndexedl Reginsta lct mode The address af fie data s obtained by adding" to 91 Conteuts - Then fonm that add yess teeta S looded n to A3 Paisea Push 3 Sub SP,sP,# Subtsacts 12 Contents e Pughed into Stace om Sp and esuit 1S Placd n S add 91SP0 adds o to Sp and 7-8ult iS Placed in Sta L917/ Stofea je conteuts of n after Scanned with CS CamScanner

n oes Coneuts n to 1 oad 1, with a7 Conteuts u loads a wth *1+4Coreu Sta 12 cmP 1Compares 2 213 Canay lag s sct CS Conteuts fnto 13 are moved nto 10 Moves 932 moves 2 Conteuts ofA3 Mo V add s moved into a Mov SP7 ue 11 Conteuts Cs Scanne h lease ve ne CamScamer