[OpenWrt-Devel] [RFC PATCH] mvebu: compile the kernel in Thumb-2 mode for ARMv7 targets

[Rui Salvaterra]

Please ignore this one, I'll send an updated patch shortly (only for
5.4, which I've tested).

On Wed, 17 Jun 2020 at 18:37, Rui Salvaterra <rsalvaterra at gmail.com> wrote:
>
> (Sending as RFC due to the note below.)
>
> The Thumb-2 instruction set generates denser code, allowing for more efficient
> use of the cache and consequently higher execution performance.
>
> NOTE: This requires enabling a linker workaround to avoid the emission of
> R_ARM_THM_JUMP11 relocations [1] in modules, which the kernel doesn't support.
> Since this effectively implies -fno-optimize-sibling-calls [2], we're generating
> suboptimal code. While compat modules load and run correctly without this
> workaround, WireGuard fails to load with an unknown relocation 102 error.
>
> [1] https://static.docs.arm.com/ihi0044/e/IHI0044E_aaelf.pdf (page 28)
> [2] https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/arm/Makefile?h=linux-5.4.y#n129
>
> Signed-off-by: Rui Salvaterra <rsalvaterra at gmail.com>
> ---
>  target/linux/mvebu/cortexa9/config-default | 2 ++
>  1 file changed, 2 insertions(+)
>  create mode 100644 target/linux/mvebu/cortexa9/config-default
>
> diff --git a/target/linux/mvebu/cortexa9/config-default b/target/linux/mvebu/cortexa9/config-default
> new file mode 100644
> index 0000000000..6aff77fda7
> --- /dev/null
> +++ b/target/linux/mvebu/cortexa9/config-default
> @@ -0,0 +1,2 @@
> +CONFIG_THUMB2_AVOID_R_ARM_THM_JUMP11=y
> +CONFIG_THUMB2_KERNEL=y
> --
> 2.27.0
>

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