Hello,
I'm trying to implement a simple stack checking mechanism in an MSP430
multi-task environment (task scheduling/switching is subject to a custom
"OS").
Each task has its own stack space, but since there's a single address
space and the memory is small, tasks can easily overflow their stack and
corrupt "foreign" data.
The best idea I came up with for checking the overflow is adding some
explicit checking code at the beginning of each function - actually at
the end of the preamble, when SP is already lowered to reserve space for
local variables.
It would be very nice though if the compiler could generate that code
itself, for instance when the "-fstack-check" is specified on the
command line.
I tracked down the preamble generation to the expand_prologue() function
(file msp430-function.c). The global variable "flag_stack_check" is
visible and automatically set to 1 by (generic) gcc when "-fstack-check"
is specified on the command line.
The best I could do was identify the code that generates "push"
instructions for all clobbered registers and the code that explicitly
lowers SP by the required amount. My code goes next to this.
However, I'm new to gcc internals and most of my attempts to produce the
check code ended up with gcc reporting an internal bug and bailing out.
I would really appreciate any suggestions or directions for implementing
this. The resulting code should be as simple as comparing R1 to a
variable (contents of a fixed memory location) that holds the stack base
address and conditionally jump to a handling routine. To my (limited)
MSP430 asm knowledge, it shoud look like this:
push r15
mov #__stack_base, r15
cmp r1, 0(r15)
jge .Lsomething
br #_handling_routine
.Lsomething
pop r15
Best regards,
Radu Rendec
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