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

["Leif Lindholm" <leif.lindholm@linaro.org>]

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)

/
    Leif

> -- 
> 2.17.1
>