With a support entitlement you can also get direct access to our team of highly-qualified Arm experts 24-hours a day
Open a support case
I've asked is same question in stack overflow, but didn't get the response. Here goes,
Why is Stack-pointer register not reading correct value from another register? When I move a value from register (r0) to stack pointer (r13), the SP reads incorrect value. This is what is mean:
MOV R0, 10
MOV R13, R0
In this case, "A" should move to R13 but instead it gets 8. Similarly,
MOV R0, 9
MOV R13, R0
In this case R13 stores 8 instead of 9.
Here's a simple program program that demonstrates the problem,
"LDR R0, =0x3FFFFDA7\n"
"MOV R13, R0\n"
Nothing much is going on here. Just a simple function call. Inside the function I moved the address to r0. Then I moved the address to R13(SP), but instead of actual address i.e. 0x3FFFFDA7, SP received 0x3FFFFDA4.
So what is going on here? Why is Stack pointer Register reading incorrect values?
I am using ARM inline Assembly with C. The IDE is KEIL.
Thanks in advance.
Stack Pointer for armv7 must be 8byte aligned. You can write there 0 8 16 but noft 9 or 10
It is actually 4 byte align. You can also write 4, 12 etc.
Sorry 8 byte alignment is an ABI requirement for sp and all the code complies to that. Btw ARM depreciates using sp for any other purpose but stack.