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Re: [PATCH v1] xen/riscv: make calculation of stack address PC-relative
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 14 Mar 2023 17:14:39 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Gianluca Guida <gianluca@xxxxxxxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 14 Mar 2023 16:15:01 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14.03.2023 17:00, Oleksii Kurochko wrote:
> The patch is needed to keep all addresses PC-relative.
>
> Pseudoinstruction 'la' can be transformed to 'auipc/addi' or
> 'auipc/l{w|d}'. It depends on the .option directive: nopic and pic.
>
> Right now, 'la' transforms to 'auipc/l{w|d}',
I'm afraid I cannot confirm this. Is it possible that your and my gas
are configured differently (i.e. can the default of nopic vs pic vary)?
> which in case of
> cpu0_boot_stack[] will lead to the usage of _GLOBAL_OFFSET_TABLE_
> where all addresses will be without counting that it might happen
> that linker address != load address.
>
> To be sure that SP is loaded always PC-relative address
> 'la' should be changed to 'lla', which always transforms to
> 'auipc/addi'.
While I agree with the adjustment in principle, I'd like to raise the
question of the suitablity of such macro insns for purposes like the
one here. In principle I would assume it would be better if sp was
written only once, with the final value. That would then also remove
the dependency on a possibly differing default gas may be using.
Jan
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