Re: [edk2-devel] [PATCH] ArmVirtPkg/ArmVirtPrePiUniCoreRelocatable: revert to PIE linking

["Ard Biesheuvel" <ard.biesheuvel@linaro.org>]

On Thu, 5 Sep 2019 at 12:33, Laszlo Ersek <lersek@redhat.com> wrote:
>
> On 09/05/19 01:04, Ard Biesheuvel wrote:
> > In some cases, the CLANG38 toolchain profile in LTO mode emits GOT
> > based relocations in spite of our attempts to avoid this, by using
> > hidden visibility, -Bsymbolic etc.
> >
> > On AARCH64, we managed to work around this by processing the GOT
> > based relocations in GenFw. As it turns out, the same issue exists
> > on 32-bit ARM, but unfortunately, we cannot use a similar trick to
> > get rid of the GOT entry, and the relocation metadata is insufficient
> > to locate the GOT entry in the binary.
> >
> > A bit of trial and error reveals that switching the linker options from
> > -pie to -shared in commit e07092edca8442db4a941dbeea0cd196c7bf8ec9 was
> > not the best approach, and instead, we can pass -pie to the linker
> > directly (using -Wl,xxx) rather than to the compiler directly, which
> > turns out to massage the linker in the right way, and prevents if from
> > emitting GOT based relocations. Your mileage may vary ...
> >
> > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > ---
> > Let's test this on a couple of different Clang versions. If it still
> > produces problems, the only other way I see is to disable the builds
> > of platforms that incorporate this module for ARM/CLANG38 [which is
> > not the end of the world]
> >
> >  ArmVirtPkg/PrePi/ArmVirtPrePiUniCoreRelocatable.inf | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/ArmVirtPkg/PrePi/ArmVirtPrePiUniCoreRelocatable.inf b/ArmVirtPkg/PrePi/ArmVirtPrePiUniCoreRelocatable.inf
> > index 683397b7afd1..9e58e56fce09 100755
> > --- a/ArmVirtPkg/PrePi/ArmVirtPrePiUniCoreRelocatable.inf
> > +++ b/ArmVirtPkg/PrePi/ArmVirtPrePiUniCoreRelocatable.inf
> > @@ -97,4 +97,4 @@
> >    gArmTokenSpaceGuid.PcdFvBaseAddress
> >
> >  [BuildOptions]
> > -  GCC:*_*_*_DLINK_FLAGS = -shared -Wl,-Bsymbolic -Wl,-T,$(MODULE_DIR)/Scripts/PrePi-PIE.lds
> > +  GCC:*_*_*_DLINK_FLAGS = -Wl,-Bsymbolic,-pie,-T,$(MODULE_DIR)/Scripts/PrePi-PIE.lds
> >
>
> Sorry for being late to this patch, I can see [*] it's upstream alrady.
> Nonetheless:
>
> Acked-by: Laszlo Ersek <lersek@redhat.com>
>

Thanks. Since the patch is already merged, I'll find another patch to
attach it to :-)

> [*] Not from my inbox though -- I've got again too much on my plate and
> am fetching email in batches. But, between my rebasing of
> "ArmVirtPkg/PlatformBootManagerLib: unload image on
> EFI_SECURITY_VIOLATION", building it, and attempting to push it, you had
> pushed this one -- and I did notice that. :)
>
> Thanks,
> Laszlo