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Re: [PATCH v1] xen/riscv: make calculation of stack address PC-relative
- To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 14 Mar 2023 17:09:31 +0000
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Gianluca Guida <gianluca@xxxxxxxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 14/03/2023 4:00 pm, 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}', 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'.
>
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> ---
> xen/arch/riscv/riscv64/head.S | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/xen/arch/riscv/riscv64/head.S b/xen/arch/riscv/riscv64/head.S
> index 8887f0cbd4..e12d2a7cf3 100644
> --- a/xen/arch/riscv/riscv64/head.S
> +++ b/xen/arch/riscv/riscv64/head.S
> @@ -27,7 +27,7 @@ ENTRY(start)
> add t3, t3, __SIZEOF_POINTER__
> bltu t3, t4, .L_clear_bss
>
> - la sp, cpu0_boot_stack
> + lla sp, cpu0_boot_stack
I don't think this is the appropriate way forward. It's very much
smells like duct tape hiding the real bug.
~Andrew
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