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MdeModulePkg/DriverSampleDxe: Make bit fields aligned in C structure 

For a structure with a series of bit fields and used as a storage
in vfr file, and if the bit fields do not add up to the size of
the defined type.In the C code use sizeof() to get size of the
structure, the results may vary form the compiler(VS,GCC...).
But the size of the storage calculated by VfrCompiler is fixed
(calculate with alignment).To avoid the issue cased by above case,
we need to make the total width of the bit fields in the structure
aligned with the size of the defined type for these bit fields.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Dandan Bi <dandan.bi@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
This commit is contained in:
Bi, Dandan 2018-02-08 22:28:39 +08:00 committed by Liming Gao
parent ce2697abeb
commit 6b86f6f336
1 changed files with 11 additions and 0 deletions
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11
MdeModulePkg/Universal/DriverSampleDxe/NVDataStruc.h
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@ -35,6 +35,14 @@ Revision History:
#pragma pack(1) #pragma pack(1)
//
// !!! For a structure with a series of bit fields and used as a storage in vfr file, and if the bit fields do not add up to the size of the defined type.
// In the C code use sizeof() to get the size the strucure, the results may vary form the compiler(VS,GCC...).
// But the size of the storage calculated by VfrCompiler is fixed (calculate with alignment).
// To avoid above case, we need to make the total bit width in the structure aligned with the size of the defined type for these bit fields. We can:
// 1. Add bit field (with/without name) with remianing with for padding.
// 2. Add unnamed bit field with 0 for padding, the amount of padding is determined by the alignment characteristics of the members of the structure.
//
typedef struct { typedef struct {
UINT16 NestByteField; UINT16 NestByteField;
UINT8 : 1; // unamed field can be used for padding UINT8 : 1; // unamed field can be used for padding
@ -84,7 +92,9 @@ typedef struct {
UINT8 Match2; UINT8 Match2;
UINT8 GetDefaultValueFromCallBackForOrderedList[3]; UINT8 GetDefaultValueFromCallBackForOrderedList[3];
UINT8 BitCheckbox : 1; UINT8 BitCheckbox : 1;
UINT8 ReservedBits: 7; // Reserved bit fields for padding.
UINT16 BitOneof : 6; UINT16 BitOneof : 6;
UINT16 : 0; // Width 0 used to force alignment.
UINT16 BitNumeric : 12; UINT16 BitNumeric : 12;
MY_BITS_DATA MyBitData; MY_BITS_DATA MyBitData;
MY_EFI_UNION_DATA MyUnionData; MY_EFI_UNION_DATA MyUnionData;
@ -109,6 +119,7 @@ typedef struct {
UINT32 EfiBitNumeric : 4; UINT32 EfiBitNumeric : 4;
UINT32 EfiBitOneof : 10; UINT32 EfiBitOneof : 10;
UINT32 EfiBitCheckbox : 1; UINT32 EfiBitCheckbox : 1;
UINT32 : 0; // Width 0 used to force alignment.
} MY_EFI_BITS_VARSTORE_DATA; } MY_EFI_BITS_VARSTORE_DATA;
// //