Re: [PATCH 11/17] MIPS: Makefile: sign-extend TEXT_BASE value on CONFIG_64BIT

[Denis Orlov <denorl2009@gmail.com>]

On Tue, 6 Jun 2023 at 12:04, Ahmad Fatoum <a.fatoum@pengutronix.de> wrote:
>
> On 05.06.23 22:10, Denis Orlov wrote:
> > The code that uses TEXT_BASE will fail on reading truncated 32-bit
> > address if running with 64BIT enabled. As we only support running from
> > compatibility segments (i.e. no 'proper' 64-bit base addresses), simply
> > make sure the value is sign-extended when passing it as a define.
>
> Below is not really a sign extension. e.g. 0x0000_0000 would be turned
> into 0xffff_ffff_0000_0000. Is that ok?

Yeah, we can only handle KSEG0/KSEG1 segments, i.e. text base should be
somewhere in 0x8000_0000/0xa000_0000. So for those, this might be
considered a sign extension, I guess.

Regards,
Denis

>
> >
> > Signed-off-by: Denis Orlov <denorl2009@gmail.com>
> > ---
> >  arch/mips/Makefile | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/mips/Makefile b/arch/mips/Makefile
> > index bad6e574c4..65a00379ab 100644
> > --- a/arch/mips/Makefile
> > +++ b/arch/mips/Makefile
> > @@ -57,7 +57,13 @@ cflags-$(CONFIG_CPU_MIPS64_R1) += $(call cc-option,-march=mips64,-mips64 -U_MIPS
> >  cflags-$(CONFIG_CPU_MIPS64_R2) += $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64) -Wa,-mips64r2 -Wa,--trap
> >  cflags-$(CONFIG_CPU_GS232)     += $(call cc-option,-march=mips32r2,-mips32r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS32) -Wa,-mips32r2 -Wa,--trap
> >
> > -KBUILD_CPPFLAGS += -DTEXT_BASE=$(CONFIG_TEXT_BASE)
> > +ifdef CONFIG_64BIT
> > +MIPS_TEXT_BASE = $(subst 0x,0xffffffff,$(CONFIG_TEXT_BASE))
> > +else
> > +MIPS_TEXT_BASE = $(CONFIG_TEXT_BASE)
> > +endif
> > +
> > +KBUILD_CPPFLAGS += -DTEXT_BASE=$(MIPS_TEXT_BASE)
> >
> >  ifndef CONFIG_MODULES
> >  # Add cleanup flags
>
> --
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