1. Passing by-value vs. by-reference in ARM
C code equivalent assembly code
int a; section ".bss" @ .bss since a is not assigned an
a: .skip @ initial value; alloc 4 bytes
.section ".text"
int subr(int); global main
int main(void) main:
{ push {r4, lr}
a = 0; ldr r4, =a @ a = 0
a = subr( a ); mov r2, #0
return 0; str r2, [r4] @ }
ldr r0, [r4] @ call subr( a ); pass “a” by value
bl subr
str r0, [r4] @ a = return value from subr in r0
mov r0, # @ return value 0 put in r0
pop {r4, lr}
bx lr @ put lr in pc

2. Passing by-value vs. by-reference in ARM
C code equivalent assembly code
int sub( int x ) subr: add r0, r0, # @ return value = x + 1
{ bx lr
return( x + 1 ); }

3. Passing by-value vs. by-reference in ARM
C code equivalent assembly code
int a; section ".bss" @ .bss since a is not assigned an
a: .skip @ initial value; alloc 4 bytes
.section ".text"
int subr(int *); global main
int main(void) main:
{ push {r4, lr}
a = 0; ldr r4, =a @ a = 0
a = subr( &a ); mov r2, #0
return 0; str r2, [r4] @
ldr r0, r @ call subr( a ); pass “a” by ref
bl subr
str r0, [r4] @ a = return value from subr in r0
mov r0, # @ return value 0 put in r0
pop {r4, lr}
bx lr @ put lr in pc

4. Passing by-value vs. by-reference in ARM
C code equivalent assembly code
int sub( int *x ) subr:
{ ldr r1, [r0] @deref parameter
return(*x + 1); add r0, r1, # @return val in r0
} bx lr