Re: [Buildroot] [PATCH] package/wpewebkit: disable JIT for all MIPS CPUs

[Thomas Petazzoni via buildroot <buildroot@buildroot.org>]

Hello Adrian,

On Fri, 23 Aug 2024 15:29:16 +0300
Adrian Perez de Castro <aperez@igalia.com> wrote:

> -# JIT is not supported for MIPS r6, but the WebKit build system does not
> -# have a check for these processors. The same goes for ARMv5 and ARMv6.
> -# Disable JIT forcibly here and use the CLoop interpreter instead.
> +# JIT is not supported for MIPS, ARMv5, and ARMv6, but the WebKit build
> +# system does not have a check for these processors.
>  #
> +# Disable JIT forcibly here and use the CLoop interpreter instead.
>  # Also, we have to disable the sampling profiler and WebAssembly, which
>  # do NOT work with ENABLE_C_LOOP.
>  #
> -# Upstream bugs: https://bugs.webkit.org/show_bug.cgi?id=191258
> -#                https://bugs.webkit.org/show_bug.cgi?id=172765
> -#                https://bugs.webkit.org/show_bug.cgi?id=265218
> +# Upstream bug: https://bugs.webkit.org/show_bug.cgi?id=278559
>  #
> -ifeq ($(BR2_ARM_CPU_ARMV5)$(BR2_ARM_CPU_ARMV6)$(BR2_MIPS_CPU_MIPS32R6)$(BR2_MIPS_CPU_MIPS64R6),y)
> +ifeq ($(BR2_ARM_CPU_ARMV5)$(BR2_ARM_CPU_ARMV6)$(BR2_mips)$(BR2_mipsel),y)

But then do we actually need a change?

Keep in mind that here we are only disabling JIT explicitly for ARMv5,
ARMv6 and MIPS32R6/MIPS64R6 because they were misdetected as supported
by wpewebkit. Indeed wpewekit supported ARM and MIPS, but not some
variants of it.

For all other architectures, we do nothing, and wpewebit properly
decides whether it supports JIT or not. So if JIT support for MIPS has
been dropped I believe the correct change is:

-ifeq ($(BR2_ARM_CPU_ARMV5)$(BR2_ARM_CPU_ARMV6)$(BR2_MIPS_CPU_MIPS32R6)$(BR2_MIPS_CPU_MIPS64R6),y)
+ifeq ($(BR2_ARM_CPU_ARMV5)$(BR2_ARM_CPU_ARMV6),y)

but only of course once we use a version of wpewebkit that really has
dropped MIPS support.

As such, your change would potentially break: it re-enables JIT on
BR2_MIPS_CPU_MIPS64R6=y, because you disable for BR2_mips and
BR2_mipsel but there are the 32-bit variants of MIPS, and so
BR2_MIPS_CPU_MIPS64R6=y would again allow JIT.

Could you clarify if we have already updated to a version of wpewebkit
that has dropped MIPS support for JIT? If so, we should simply apply
the simpler change above.

Thanks!

Thomas
-- 
Thomas Petazzoni, co-owner and CEO, Bootlin
Embedded Linux and Kernel engineering and training
https://bootlin.com
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