Question

I am trying to pass more than four parameters from my C++ code to Assembly.

The C++ function looks like :

static float armFunction(float, float, float, float, float);

I can retrieve the first four parameters from the registers r0-r3 without any problem.

I expect that my fifth float argument is on the stack and i should be able to access it using the stack pointer sp e.g. I try to load my fifth argument in r4 like :

ldr r4, [sp]

or even:

ldr r4, [sp, #-0x4]

But this doesn’t work and the assembly code immediately exits with some stack corruption output.

My complete assembly code looks like this here: http://pastie.org/3933875

Answer 1

My asm code has no trouble reading the 5th parameter from a JNI call from C to asm. Here are the first 2 lines of my asm function:

  stmfd    sp!,{r4-r12,lr}
  ldr      r12,[sp,#40]   @ first stack variable

In the case where you’re not needing to preserve any registers, the 5th parameter is on the top of the stack:

  ldr r12,[sp]