Re: [PATCH] MdeModulePkg/FileExplorerLib: avoid packed struct for program data

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

On Mon, Dec 10, 2018 at 02:39:01PM +0000, Gao, Liming wrote:
> Ard:
>   I agree this change.
> 
> Leif:
>   On the duplicated definition of HII_VENDOR_DEVICE_PATH,
>   MdeModulePkg DriverSampleDxe first defines it and use it as the
>   driver level definition. Other UEFI HII driver may refer to the
>   driver sample driver and define the same structure. One
>   centralized header file can be defined for the default HII vendor
>   device path. If the driver wants to use the different one, it can
>   define its own structure.

Exactly. You're correct, my comment was imprecise. But the fact that
29 locations use the same default HII vendor device patch definition
suggests that there would be value in having a centralised default to
refer to.

I raised https://bugzilla.tianocore.org/show_bug.cgi?id=1388

Actually, I found there are 3 more in edk2-platforms :)

https://bugzilla.tianocore.org/show_bug.cgi?id=1389

Regards,

Leif

> 
> Thanks
> Liming
> > -----Original Message-----
> > From: edk2-devel [mailto:edk2-devel-bounces@lists.01.org] On Behalf Of Leif Lindholm
> > Sent: Monday, December 10, 2018 8:26 PM
> > To: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > Cc: Wu, Hao A <hao.a.wu@intel.com>; Ni, Ruiyu <ruiyu.ni@intel.com>; edk2-devel@lists.01.org
> > Subject: Re: [edk2] [PATCH] MdeModulePkg/FileExplorerLib: avoid packed struct for program data
> > 
> > On Sat, Dec 08, 2018 at 11:24:31AM +0100, Ard Biesheuvel wrote:
> > > Struct packing is only necessary for data structures whose in-memory
> > > representation is covered by the PI or UEFI specs, and may deviate
> > > from the ordinary C rules for alignment.
> > >
> > > So in case of FileExplorerLib, this applies to the device path struct
> > > only, and other structures used to carry program data should not be
> > > packed, or we may end up with alignment faults on architectures such
> > > as ARM, which don't permit load/store double or multiple instructions
> > > to access memory locations that are not 32-bit aligned.
> > >
> > > E.g., the following call in FileExplorerLibConstructor()
> > >
> > >   InitializeListHead (&gFileExplorerPrivate.FsOptionMenu->Head);
> > >
> > > which is emitted as follows for 32-bit ARM/Thumb2 by Clang-5.0
> > >
> > >     3de0:       b510            push    {r4, lr}
> > >     3de2:       4604            mov     r4, r0
> > >     ...
> > >     3de8:       e9c4 4400       strd    r4, r4, [r4]
> > >     3dec:       bd10            pop     {r4, pc}
> > >
> > > will perform a double-word store on the first argument, passed in
> > > register r0, assuming that the pointer type of the argument is
> > > enough to guarantee that the value is suitably aligned.
> > >
> > > Contributed-under: TianoCore Contribution Agreement 1.1
> > > Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> > 
> > I agree with the architectural rationale.
> > 
> > However, I also decided to have a look.
> > 
> > $ git grep "} HII_VENDOR_DEVICE_PATH;"
> > EdkCompatibilityPkg/Compatibility/FrameworkHiiOnUefiHiiThunk/HiiDatabase.h:} HII_VENDOR_DEVICE_PATH;
> > EdkCompatibilityPkg/Foundation/Library/Dxe/UefiEfiIfrSupportLib/UefiIfrLibrary.h:} HII_VENDOR_DEVICE_PATH;
> > EmbeddedPkg/Drivers/ConsolePrefDxe/ConsolePrefDxe.c:} HII_VENDOR_DEVICE_PATH;
> > EmbeddedPkg/Drivers/DtPlatformDxe/DtPlatformDxe.c:} HII_VENDOR_DEVICE_PATH;
> > IntelFrameworkModulePkg/Library/LegacyBootMaintUiLib/LegacyBootMaintUi.h:} HII_VENDOR_DEVICE_PATH;
> > IntelFrameworkModulePkg/Universal/BdsDxe/Bds.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Application/UiApp/Ui.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Library/BootMaintenanceManagerUiLib/BootMaintenanceManager.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Library/BootManagerUiLib/BootManager.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Library/DeviceManagerUiLib/DeviceManager.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Library/FileExplorerLib/FileExplorer.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Library/PlatformVarCleanupLib/PlatVarCleanup.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Universal/Disk/RamDiskDxe/RamDiskImpl.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Universal/DriverSampleDxe/DriverSample.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Universal/HiiResourcesSampleDxe/HiiResourcesSample.c:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Universal/Network/IScsiDxe/IScsiConfig.h:} HII_VENDOR_DEVICE_PATH;
> > MdeModulePkg/Universal/PlatformDriOverrideDxe/PlatDriOverrideDxe.c:} HII_VENDOR_DEVICE_PATH;
> > NetworkPkg/IScsiDxe/IScsiConfig.h:} HII_VENDOR_DEVICE_PATH;
> > NetworkPkg/TlsAuthConfigDxe/TlsAuthConfigImpl.h:} HII_VENDOR_DEVICE_PATH;
> > QuarkPlatformPkg/Platform/Dxe/Setup/SetupPlatform.h:} HII_VENDOR_DEVICE_PATH;
> > SecurityPkg/Tcg/Opal/OpalPassword/OpalHii.h:} HII_VENDOR_DEVICE_PATH;
> > SecurityPkg/Tcg/Tcg2Config/Tcg2ConfigImpl.h:} HII_VENDOR_DEVICE_PATH;
> > SecurityPkg/Tcg/TcgConfigDxe/TcgConfigImpl.h:} HII_VENDOR_DEVICE_PATH;
> > SecurityPkg/UserIdentification/PwdCredentialProviderDxe/PwdCredentialProvider.h:} HII_VENDOR_DEVICE_PATH;
> > SecurityPkg/UserIdentification/UserIdentifyManagerDxe/UserIdentifyManager.h:} HII_VENDOR_DEVICE_PATH;
> > SecurityPkg/UserIdentification/UserProfileManagerDxe/UserProfileManager.h:} HII_VENDOR_DEVICE_PATH;
> > SecurityPkg/VariableAuthenticated/SecureBootConfigDxe/SecureBootConfigImpl.h:} HII_VENDOR_DEVICE_PATH;
> > Vlv2TbltDevicePkg/Library/PlatformBdsLib/BdsPlatform.h:} HII_VENDOR_DEVICE_PATH;
> > Vlv2TbltDevicePkg/PlatformSetupDxe/PlatformSetupDxe.c:} HII_VENDOR_DEVICE_PATH;
> > 
> > Now, I will confess to being lazy and not manually checking all of
> > them, but 100% of the ones I did check were identical (except in
> > packedness).
> > 
> > Does this definition belong in a central header somewhere rather than
> > in 29 (and counting) different locations, implemented differently?
> > 
> > /
> >     Leif
> > 
> > > ---
> > >  MdeModulePkg/Library/FileExplorerLib/FileExplorer.h | 4 ++--
> > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/MdeModulePkg/Library/FileExplorerLib/FileExplorer.h b/MdeModulePkg/Library/FileExplorerLib/FileExplorer.h
> > > index bf1450dbd581..603185abe4b1 100644
> > > --- a/MdeModulePkg/Library/FileExplorerLib/FileExplorer.h
> > > +++ b/MdeModulePkg/Library/FileExplorerLib/FileExplorer.h
> > > @@ -51,6 +51,8 @@ typedef struct {
> > >    EFI_DEVICE_PATH_PROTOCOL       End;
> > >  } HII_VENDOR_DEVICE_PATH;
> > >
> > > +#pragma pack()
> > > +
> > >  typedef struct {
> > >    EFI_HANDLE                        DeviceHandle;
> > >    EFI_DEVICE_PATH_PROTOCOL          *DevicePath;
> > > @@ -100,8 +102,6 @@ typedef struct {
> > >
> > >  #define FILE_EXPLORER_PRIVATE_FROM_THIS(a)  CR (a, FILE_EXPLORER_CALLBACK_DATA, FeConfigAccess,
> > FILE_EXPLORER_CALLBACK_DATA_SIGNATURE)
> > >
> > > -#pragma pack()
> > > -
> > >  extern UINT8    FileExplorerVfrBin[];
> > >
> > >  #define MENU_OPTION_SIGNATURE      SIGNATURE_32 ('m', 'e', 'n', 'u')
> > > --
> > > 2.19.2
> > >
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