I am trying to play around with an app for Android and every time I try to call a function (
lua_gettop() from the Lua 5.1 library) from the app's address space, it hits me with ILL_ILLOPC.
I made sure to rebase the address and the function is correct as I read the opcodes from the location to make sure I wasn't calling the wrong thing. I tried to call
gettop() by using another function that is only designed to call that, and it worked, so I remade
gettop() and built it with my current tools and put both libraries in IDA to compare the instructions.
To my surprise they were completely different (which makes me think that is why my trying to call that crashes, it doesn't recognise the instructions??)
Here are the instructions
.text:0172D8F8 LDRD.W R1, R0, [R0,#0xC] .text:0172D8FC SUBS R0, R1, R0 .text:0172D8FE ASRS R0, R0, #4 .text:0172D900 BX LR
And my library's version of the function:
.text:000BF614 LDR R1, [R0,#0xC] .text:000BF618 LDR R0, [R0,#0x10] .text:000BF61C SUB R0, R1, R0 .text:000BF620 MOV R0, R0,LSR#4 .text:000BF624 BX LR
I tried to find out how to make it compile to the same instruction set to no luck, I assume this to be the problem, but I'm ready to be corrected.