On Tue, 11 Dec 2018 at 02:48, Wu, Hao A <[email protected]> wrote: > > > -----Original Message----- > > From: Ard Biesheuvel [mailto:[email protected]] > > Sent: Saturday, December 08, 2018 6:25 PM > > To: [email protected] > > Cc: Wang, Jian J; Wu, Hao A; Ni, Ruiyu; Ard Biesheuvel > > Subject: [PATCH] MdeModulePkg/FileExplorerLib: avoid packed struct for > > program data > > > > 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 <[email protected]> > > --- > > 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() > > - > > Reviewed-by: Hao Wu <[email protected]> > > Best Regards, > Hao Wu >
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