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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 <ard.biesheuvel@linaro.org>
Reviewed-by: Hao Wu <hao.a.wu@intel.com>
This commit is contained in:
Ard Biesheuvel 2018-12-08 11:24:31 +01:00
parent f0574a194c
commit 765fb87c2b
1 changed files with 2 additions and 2 deletions
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4
MdeModulePkg/Library/FileExplorerLib/FileExplorer.h
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@ -51,6 +51,8 @@ typedef struct {
EFI_DEVICE_PATH_PROTOCOL End; EFI_DEVICE_PATH_PROTOCOL End;
} HII_VENDOR_DEVICE_PATH; } HII_VENDOR_DEVICE_PATH;
#pragma pack()
typedef struct { typedef struct {
EFI_HANDLE DeviceHandle; EFI_HANDLE DeviceHandle;
EFI_DEVICE_PATH_PROTOCOL *DevicePath; 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) #define FILE_EXPLORER_PRIVATE_FROM_THIS(a) CR (a, FILE_EXPLORER_CALLBACK_DATA, FeConfigAccess, FILE_EXPLORER_CALLBACK_DATA_SIGNATURE)
#pragma pack()
extern UINT8 FileExplorerVfrBin[]; extern UINT8 FileExplorerVfrBin[];
#define MENU_OPTION_SIGNATURE SIGNATURE_32 ('m', 'e', 'n', 'u') #define MENU_OPTION_SIGNATURE SIGNATURE_32 ('m', 'e', 'n', 'u')