Re: [edk2-devel] [PATCH 4/5] StandaloneMmPkg: generate position independent code for StMM core

["Yao, Jiewen" <jiewen.yao@intel.com>]

Acked-by: Jiewen Yao <Jiewen.yao@intel.com>

I hope GCC expert can review this and double confirm.

Thank you
Yao Jiewen

> -----Original Message-----
> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Ard
> Biesheuvel
> Sent: Wednesday, June 10, 2020 4:18 PM
> To: devel@edk2.groups.io
> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>; Kinney, Michael D
> <michael.d.kinney@intel.com>; Gao, Liming <liming.gao@intel.com>; Yao,
> Jiewen <jiewen.yao@intel.com>; Sami Mujawar <sami.mujawar@arm.com>;
> Ilias Apalodimas <ilias.apalodimas@linaro.org>
> Subject: [edk2-devel] [PATCH 4/5] StandaloneMmPkg: generate position
> independent code for StMM core
> 
> The standalone MM core runs in a restricted environment that is set
> up by a higher privilege level, and which may not allow memory regions
> to be writable and executable at the same time.
> 
> This means that making the StMM core self-relocatable requires that
> all the targets of the relocation fixups are outside of the executable
> region of the image, given that we cannot remap the executable code
> writable from the executable code itself without losing those execute
> permissions.
> 
> So instead, use the existing toolchain support to ensure that position
> independent code is used where possible, and that all the remaining
> relocated quantities are emitted into the data section. (Note that
> staticallly initialized const pointers will be emitted into the
> .data.rel.ro section, which gets pulled into the .data section by
> our linker script)
> 
> To ensure that we don't pick up any absolute references in executable
> code inadvertently (e.g., in assembler code), add the '-z text' linker
> option which will force the build to fail in this case.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
> ---
>  StandaloneMmPkg/Core/StandaloneMmCore.inf                                         | 4 ++++
> 
> StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCoreE
> ntryPoint.inf | 3 +++
>  2 files changed, 7 insertions(+)
> 
> diff --git a/StandaloneMmPkg/Core/StandaloneMmCore.inf
> b/StandaloneMmPkg/Core/StandaloneMmCore.inf
> index d17ff9965bdc..87bf6e9440a7 100644
> --- a/StandaloneMmPkg/Core/StandaloneMmCore.inf
> +++ b/StandaloneMmPkg/Core/StandaloneMmCore.inf
> @@ -75,3 +75,7 @@ [Guids]
>    gEfiEventLegacyBootGuid
> 
>    gEfiEventExitBootServicesGuid
> 
>    gEfiEventReadyToBootGuid
> 
> +
> 
> +[BuildOptions]
> 
> +  GCC:*_*_*_CC_FLAGS = -fpie
> 
> +  GCC:*_*_*_DLINK_FLAGS = -Wl,-z,text,-Bsymbolic,-pie
> 
> diff --git
> a/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCor
> eEntryPoint.inf
> b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCor
> eEntryPoint.inf
> index 891c292e92f8..7d6ee4e08ecb 100644
> ---
> a/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCor
> eEntryPoint.inf
> +++
> b/StandaloneMmPkg/Library/StandaloneMmCoreEntryPoint/StandaloneMmCor
> eEntryPoint.inf
> @@ -48,3 +48,6 @@ [Guids]
>    gEfiMmPeiMmramMemoryReserveGuid
> 
>    gEfiStandaloneMmNonSecureBufferGuid
> 
>    gEfiArmTfCpuDriverEpDescriptorGuid
> 
> +
> 
> +[BuildOptions]
> 
> +  GCC:*_*_*_CC_FLAGS = -fpie
> 
> --
> 2.26.2
> 
> 
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