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

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

On Thu, 5 Sep 2019 at 07:19, Leif Lindholm <leif.lindholm@linaro.org> wrote:
>
> On Wed, Sep 04, 2019 at 04:04:23PM -0700, 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.in
> > 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
>
> We already merged a fix for AARCH64 though - could/should this be
> active on ARM only?
>
> A problem I have with this patch is that ArmVirtQemuKernel curently
> doesn't boot on my qemu (with/without kvm, built with GCC5 or CLANG38,
> with or without this patch):
> ProcessPciHost: Config[0x4010000000+0x10000000) Bus[0x0..0xFF]
> Io[0x0+0x10000)@0x3EFF0000 Mem32[0x10000000+0x2EFF0000)@0x0
> Mem64[0x8000000000+0x8000000000)@0x0
> MapGcdMmioSpace: failed to set memory space attributes for region
> [0x4010000000+0x10000000)
>
> ASSERT_EFI_ERROR (Status = Unsupported)
> ASSERT [PciHostBridgeDxe]
> /work/git/edk2/ArmVirtPkg/Library/FdtPciHostBridgeLib/FdtPciHostBridgeLib.c(293):
> !EFI_ERROR (Status)
> qemu-system-arm: terminating on signal 15 from pid 4680 (killall)
>

Does it work with -M virt,highmem=off ?