Useful patch to integrate

Hi,

Would you provide a small demo to demonstrate the usage of this patch? It seems this is a very old patch (originally proposed in 2011) and did not get enough response in gcc patch mailing list.

BR,
Tony

Yes it didn't get much attention from anyone maintaining ARM, and requires someone with better gcc knowledge than me to do a complete port to 4.9. I have the direct path using a global register working, but the path using a symbol lookup is failing badly.

Not sure what you're expecting for a 'demo', but we have custom O/S and we don't use the MPU, so checking/detecting if any thread overflows the allocated stack this patch/approach is very useful. Basically I reserver a register for this (but like I mentioned a symbol could be used too) and on every context switch and change the value to be the base of the stack for that thread, gcc then generates a check and jump if the stack is overflowed in every function prologue, e.g.:

ifeq ($(CONFIG_GCC_STACK_CHECK), y)
 EXTRA_CFLAGS += -ffixed-r10
 EXTRA_CFLAGS += -fstack-check=direct -fstack-limit-register=r10
endif

void *ktable_alloc(ktable_t *kt)
{
     3a8: e92d 43f0 stmdb sp!, {r4, r5, r6, r7, r8, r9, lr}
     3ac: 45d5 cmp sp, sl
     3ae: d201 bcs.n 3b4 <ktable_alloc+0xc>
     3b0: f004 ffc6 bl 5340 <__thumb_stack_failure>

So, if the stack pointer has overflowed the call to __thumb_stack_failure is triggered.

Regards,
Ahmed.

Hi,

We will study this patch to see whether we can port it or not. Thanks for the information.

BR,
Tony

http://pastebin.com/NxhTXDjc

Just wanted to share my version of the patch in-case it's useful, it makes the path I gave an example to above work. Can we create a bug/feature request for this?

Thanks,
Ahmed

An updated patch, symbol lookup working too.

ifeq ($(CONFIG_GCC_STACK_CHECK), y)
 EXTRA_CFLAGS += -fstack-check=indirect -fstack-limit-symbol=current_stack
endif

http://pastebin.com/raw.php?i=ujMY6R5F

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