[llvm-dev] LLVM Backend for a platform with no (normal) stack

Bruce Hoult via llvm-dev
Fri, 14 Dec 2018 20:27:11 -0000

You said you can allocate memory?

On Fri, Dec 14, 2018 at 12:09 PM JD Jones <jjones at prc-hsv.com> wrote:

> Thanks, no malloc or free equivalents either (no heap).
>
>
>
> So, there are no others (to your knowledge) who have built an LLVM backend
> for a platform with no “normal” stack?  I found a presentation about some
> FPGA work (using LLVM) but it doesn’t seem to apply to my platform. Perhaps
> someone else on the mailing list will have come across this rarity?
>
>
>
> Thank you again for your time and responses. If I have inadvertently been
> rude, please forgive someone new to LLVM? And if your forgiveness stretches
> that far, perhaps you could clue me on just how I was rude so that I can
> avoid it in the future?
>
>
>
> More thanks,
>
> JD Jones
>
>
>
> *From:* Bruce Hoult [mailto:brucehoult at sifive.com]
> *Sent:* Friday, December 14, 2018 1:29 PM
> *To:* jjones at prc-hsv.com
> *Cc:* LLVM Developers Mailing List <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] LLVM Backend for a platform with no (normal)
> stack
>
>
>
> Having your function prologue call malloc() and epilogue call free() (or
> similar functions) instead of bumping a stack pointer is not a problem.
> That stuff is generated explicitly by ISA-specific code anyway.
>
>
>
> On Fri, Dec 14, 2018 at 9:05 AM JD Jones <jjones at prc-hsv.com>
wrote:
>
> Thanks for your response.  Please see below.
>
>
>
> *From:* Bruce Hoult [mailto:brucehoult at sifive.com]
> *Sent:* Thursday, December 13, 2018 5:58 PM
> *To:* jjones at prc-hsv.com
> *Cc:* LLVM Developers Mailing List <llvm-dev at lists.llvm.org>
> *Subject:* Re: [llvm-dev] LLVM Backend for a platform with no (normal)
> stack
>
>
>
> Do you have a register that you can store a memory address
>
> >> yes
>
>
>
> in and an addressing mode that allows you to add (or subtract) a constant
> to that register
>
> >> Sometimes
>
>
>
> and use the address calculated to load//store from memory? Do you have
> enough registers that you can keep one of them permanently pointed to a
> particular memory region?
>
> >> No
>
>
>
> The platform intentionally does not allow use of some large chunk of
> memory for shared use by function calls.  I can allocate memory (so long as
> I know the necessary size before-hand). I can work around this issue, but
> if someone has already addressed it, I’d like to learn from their
> experiences before rolling my own.
>
>
>
> If yes, then you have a stack to exactly the same extent as RISC-V or MIPS
> do.
>
>
>
> On Thu, Dec 13, 2018 at 12:53 PM JD Jones via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
> Dear Sir or Ma’am;
>
>
>
> I have found a wealth of help and information on writing an LLVM backend.
> And, my platform has no stack.
>
>
>
> Can you point me to any information that would specifically address
> creating a backend for this kind of platform?
>
>
>
> In previous wanderings, I thought I ran across a phrase “platforms with no
> stack such as FPGAs”, but I can’t find that mention, now.
>
>
>
> More thanks than I can type,
>
> JD Jones
>
> Software Engineer
>
>
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