Question

Write the following code in ARM 32 *AND* 64 bit assembly. Be sure to follow C calling conventions. char *strcpy(char *dst, char *src) { char *dst_copy = dst; while (*src) { (*dst) = (*src) ++dst; ++src; (*dst) = (*src) return dst_copy;

Please provide comments for each line, to make it easier to understand.

Thank you!

Answer 1

Here is your C Code:

char *strcpy(char *dst,char *src) { char *dst_copy=dst; // character pointer declaration while(*src) // loop to traverse the src { (*dst)=(*src); ++dst; ++src; } (*dst)=(*src); return dst_copy; // returning the copied character array }

char *strcpy(char *dst, char *src) { char *dst_copy=dst; // character pointer declaration while(*src) // loop to traverse the src (*dst)=(src); ++dst; ++src; (*dst)=("src); return dst_copy; // returning the copied character array 11

Here is the converted Code:

strcpy: push rbp mov rbp, rsp mov QWORD PTR [rbp-24], rdi mov QWORD PTR [rbp-32], rsi mov rax, QWORD PTR [rbp-24] mov QWORD PTR [rbp-8], rax jmp .L2 .L3: mov rax, QWORD PTR [rbp-32] movzx edx, BYTE PTR [rax] mov rax, QWORD PTR [rbp-24] mov BYTE PTR [rax], dl add QWORD PTR [rbp-24], 1 add QWORD PTR [rbp-32], 1 .L2: mov rax, QWORD PTR [rbp-32] movzx eax, BYTE PTR [rax] test al, al jne .L3 mov rax, QWORD PTR [rbp-32] movzx edx, BYTE PTR [rax] mov rax, QWORD PTR [rbp-24] mov BYTE PTR [rax], dl mov rax, QWORD PTR [rbp-8] pop rbp ret

1 strcpy: push mov mov mov mov mov jmp rbp rbp, rsp QWORD PTR [rbp-24), rdi QWORD PTR (rbp-32], rsi rax, QWORD PTR (rbp-24] QWORD PTR [rbp-8], rax .L2 mov movzx mov mov add add rax, QWORD PTR (rbp-32] edx, BYTE PTR [rax] rax, QWORD PTR [rbp-24] BYTE PTR [rax), dl QWORD PTR [rbp-24], 1 QWORD PTR [rbp-32], 1 mov movzx test jne mov movzx mov mov mov pop ret rax, QWORD PTR [rbp-32] eax, BYTE PTR [rax] al, al .L3 rax, QWORD PTR (rbp-32] edx, BYTE PTR [rax] rax, QWORD PTR (rbp-24] BYTE PTR [rax), dl rax, QWORD PTR (rbp-8] rbp

*** If you have any doubts regarding the solution, please do ask in the comments ***