Re: [PATCH v5 7/8] MdePkg GCC/X64: avoid 'hidden' visibility for module entry points

["Gao, Liming" <liming.gao@intel.com>]

Ard:
  I don't think it is good way to define GCC_VISIBILITY_PROTECTED and apply it in EntryPointLib. We only need to expose _ModuleEntryPoint. It has been specified in LINK_FLAGS in tools_def.txt. Could we also specify its attribute in CC_FLAGS or LINK_FLAGS in tools_def.txt?

Thanks
Liming
> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of
> Ard Biesheuvel
> Sent: Monday, August 01, 2016 4:02 PM
> To: Shi, Steven ; Zhu, Yonghong
> ; Gao, Liming ; Justen,
> Jordan L ; edk2-devel@lists.01.org
> Cc: lersek@redhat.com; leif.lindholm@linaro.org; Ard Biesheuvel
>
> Subject: [edk2] [PATCH v5 7/8] MdePkg GCC/X64: avoid 'hidden' visibility for
> module entry points
>
> When building with LTO enabled, the LTO routines infer from the 'hidden'
> visibility of the _ModuleEntryPoint symbol that its code only needs to be
> retained if it is referenced internally, and disregards the fact that
> it is referenced by the entry point field in the ELF metadata.
>
> This is arguably a bug in LTO, but we can work around it by ensuring that
> the _ModuleEntryPoint symbol is emitted with protected visibility instead.
>
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel
> ---
> MdePkg/Include/X64/ProcessorBind.h | 9 ++++++++-
> MdePkg/Library/DxeCoreEntryPoint/DxeCoreEntryPoint.inf | 2 ++
> MdePkg/Library/PeiCoreEntryPoint/PeiCoreEntryPoint.inf | 2 ++
> MdePkg/Library/PeimEntryPoint/PeimEntryPoint.inf | 2 ++
> MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf | 2
> ++
> MdePkg/Library/UefiDriverEntryPoint/UefiDriverEntryPoint.inf | 2 ++
> 6 files changed, 18 insertions(+), 1 deletion(-)
>
> diff --git a/MdePkg/Include/X64/ProcessorBind.h
> b/MdePkg/Include/X64/ProcessorBind.h
> index 666cc8e8bd16..e45b9cba2bb3 100644
> --- a/MdePkg/Include/X64/ProcessorBind.h
> +++ b/MdePkg/Include/X64/ProcessorBind.h
> @@ -29,13 +29,20 @@
>
> #if defined(__GNUC__) && defined(__pic__)
> //
> -// Mark all symbol declarations and references as hidden, meaning they will
> +// Mark all symbol declarations and references as hidden*, meaning they
> will
> // not be subject to symbol preemption. This allows the compiler to refer to
> // symbols directly using relative references rather than via the GOT, which
> // contains absolute symbol addresses that are subject to runtime relocation.
> //
> +// * Under LTO, the entry point of a module must have protected or default
> +// visibility to prevent it from being pruned.
> +//
> +#ifdef GCC_VISIBILITY_PROTECTED
> +#pragma GCC visibility push (protected)
> +#else
> #pragma GCC visibility push (hidden)
> #endif
> +#endif
>
> #if defined(__INTEL_COMPILER)
> //
> diff --git a/MdePkg/Library/DxeCoreEntryPoint/DxeCoreEntryPoint.inf
> b/MdePkg/Library/DxeCoreEntryPoint/DxeCoreEntryPoint.inf
> index 01f64c34c7a1..2d6f87ed062e 100644
> --- a/MdePkg/Library/DxeCoreEntryPoint/DxeCoreEntryPoint.inf
> +++ b/MdePkg/Library/DxeCoreEntryPoint/DxeCoreEntryPoint.inf
> @@ -39,3 +39,5 @@ [LibraryClasses]
> BaseLib
> DebugLib
>
> +[BuildOptions]
> + GCC:*_*_X64_CC_FLAGS = -DGCC_VISIBILITY_PROTECTED
> diff --git a/MdePkg/Library/PeiCoreEntryPoint/PeiCoreEntryPoint.inf
> b/MdePkg/Library/PeiCoreEntryPoint/PeiCoreEntryPoint.inf
> index d920306713c5..4e61783b3bd5 100644
> --- a/MdePkg/Library/PeiCoreEntryPoint/PeiCoreEntryPoint.inf
> +++ b/MdePkg/Library/PeiCoreEntryPoint/PeiCoreEntryPoint.inf
> @@ -37,3 +37,5 @@ [LibraryClasses]
> BaseLib
> DebugLib
>
> +[BuildOptions]
> + GCC:*_*_X64_CC_FLAGS = -DGCC_VISIBILITY_PROTECTED
> diff --git a/MdePkg/Library/PeimEntryPoint/PeimEntryPoint.inf
> b/MdePkg/Library/PeimEntryPoint/PeimEntryPoint.inf
> index a2db9e058bbe..adfd91bdc57e 100644
> --- a/MdePkg/Library/PeimEntryPoint/PeimEntryPoint.inf
> +++ b/MdePkg/Library/PeimEntryPoint/PeimEntryPoint.inf
> @@ -37,3 +37,5 @@ [Packages]
> [LibraryClasses]
> DebugLib
>
> +[BuildOptions]
> + GCC:*_*_X64_CC_FLAGS = -DGCC_VISIBILITY_PROTECTED
> diff --git
> a/MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
> b/MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
> index be92b3dc0760..9525c55c2051 100644
> ---
> a/MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
> +++
> b/MdePkg/Library/UefiApplicationEntryPoint/UefiApplicationEntryPoint.inf
> @@ -38,3 +38,5 @@ [LibraryClasses]
> DebugLib
> BaseLib
>
> +[BuildOptions]
> + GCC:*_*_X64_CC_FLAGS = -DGCC_VISIBILITY_PROTECTED
> diff --git a/MdePkg/Library/UefiDriverEntryPoint/UefiDriverEntryPoint.inf
> b/MdePkg/Library/UefiDriverEntryPoint/UefiDriverEntryPoint.inf
> index 7a9dcbcd4df2..8d30b1197850 100644
> --- a/MdePkg/Library/UefiDriverEntryPoint/UefiDriverEntryPoint.inf
> +++ b/MdePkg/Library/UefiDriverEntryPoint/UefiDriverEntryPoint.inf
> @@ -65,3 +65,5 @@ [Depex.common.UEFI_DRIVER]
> gEfiVariableArchProtocolGuid AND
> gEfiWatchdogTimerArchProtocolGuid
>
> +[BuildOptions]
> + GCC:*_*_X64_CC_FLAGS = -DGCC_VISIBILITY_PROTECTED
> --
> 2.7.4
>
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