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Safe to use r13-r15 as general register?

Yang Fang
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Note: This was originally posted on 18th July 2011 at http://forums.arm.com

Hello, I am writting a function, which involves complicated algorithm, I want to have a lot of general purpose registers to keep the routine speed. I have read some article that r13-r15 are special registers, but can be used as general purpose registers.

Can I do it like this
   stmfd       sp!, {r4-r15,lr}
:
:
    ldmfd       sp!, {r4-r15,pc}

Thank you very much!
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    Note: This was originally posted on 19th July 2011 at http://forums.arm.com

    But it's important to understand that that code is not re-entrant: that is, if my_fct is interrupted and the interrupt calls (possibly indirectly) my_fct again then the when the outer call to my_fct tries to return, bad things™ will happen.
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    Note: This was originally posted on 19th July 2011 at http://forums.arm.com

    But it's important to understand that that code is not re-entrant: that is, if my_fct is interrupted and the interrupt calls (possibly indirectly) my_fct again then the when the outer call to my_fct tries to return, bad things™ will happen.
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