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

[Laszlo Ersek]

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 at 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 at redhat.com>

[*] 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

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