Question

I am trying to execute a binary wrapped inside my own assembly code, there are reasons like i want to do some init and see how the binary behaves, however i am unable to execute the binary even without any such init, no output on uart, lcd (I am running an arm cortexa-8 based qsd8250b chipset powering a mdp[mobile development platform]) I know the wrapped binary runs perfectly on my board since i have used it earlier (less than a day ago).

Problem is, i am unsure/info is not available regarding where the binary is loaded in memory.

This is my code so far

.org 0
.type _start,#function
.globl _start
_start:
   b   main
@@ Snipped headers @@
.org   0x1000
main:
   mov r9, pc             @r9= address of loadlk in memory
   ldr r2, =loadlk        @r2= address of loadlk in objfile
loadlk:
   sub r0, r9, r2         @r0= r9-r2 = address of _start in memory
   add r0, r0, #0x1200    @r0= r0 + 0x1200 = lkbin_start (src)
   add r3, r0, #0xD000    @r3= r0 + 0xd000 = lkbin_start + ~sz(lk.bin) = lkbin_end (end)
cpy:
   ldr r1, =0x28000000    @r1= destination (dst)
   ldr r2, [r0],#4
   str r2, [r1],#4
   cmp r0, r3             @current read address ?= end, r0 < r3 -> branch back
   blo cpy
   ldr r9, =0x28000000
   ldr r4, =0xa9000864    @Flashlight
   ldr r5, =0xa9000814
   ldr r4, [r4, #0]
   orr r6, r4, #0x200000
   str r6, [r5, #0]
   dsb sy
   isb sy
   bx  r9
   b   .
.ltorg
.org 0x1200
lkbin_start:
.incbin  "lk.bin"
lkbin_end:
.align 8

and this is my compile script

arm-none-eabi-as bootwrapper.S -o bootwrapper.o
arm-none-eabi-objcopy -O binary bootwrapper.o binary

It sure does reach the flashlight code as i see my flashlight blink, but then nothing happens, from what i can think it copies trash code to the target and tries to execute it.

Any help ?

Answer 1

Okay, i didn’t know i could be this silly at night…

cpy:
   ldr r1, =0x28000000    @r1= destination (dst)
   ldr r2, [r0],#4
   str r2, [r1],#4
   cmp r0, r3             @current read address ?= end, r0 < r3 -> branch back
   blo cpy

As the loop went on, r1 always had the value 0x28000000, so all data was written to one single location in memory overwriting the previous contents… how stupid.