Reviewed-by: Liming Gao <liming....@intel.com> >-----Original Message----- >From: Bi, Dandan >Sent: Thursday, February 08, 2018 10:29 PM >To: edk2-devel@lists.01.org >Cc: Dong, Eric <eric.d...@intel.com>; Gao, Liming <liming....@intel.com> >Subject: [patch] 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.d...@intel.com> >Cc: Liming Gao <liming....@intel.com> >Contributed-under: TianoCore Contribution Agreement 1.1 >Signed-off-by: Dandan Bi <dandan...@intel.com> >--- > MdeModulePkg/Universal/DriverSampleDxe/NVDataStruc.h | 11 >+++++++++++ > 1 file changed, 11 insertions(+) > >diff --git a/MdeModulePkg/Universal/DriverSampleDxe/NVDataStruc.h >b/MdeModulePkg/Universal/DriverSampleDxe/NVDataStruc.h >index 40fb3d0..af3d4bc 100644 >--- a/MdeModulePkg/Universal/DriverSampleDxe/NVDataStruc.h >+++ b/MdeModulePkg/Universal/DriverSampleDxe/NVDataStruc.h >@@ -33,10 +33,18 @@ Revision History: > #define CONFIGURATION_VARSTORE_ID 0x1234 > #define BITS_VARSTORE_ID 0x2345 > > #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 { > UINT16 NestByteField; > UINT8 : 1; // unamed field can be used for padding > UINT8 NestBitCheckbox : 1; > UINT8 NestBitOneof : 2; >@@ -82,11 +90,13 @@ typedef struct { > EFI_HII_TIME Time; > UINT8 RefreshGuidCount; > UINT8 Match2; > UINT8 GetDefaultValueFromCallBackForOrderedList[3]; > UINT8 BitCheckbox : 1; >+ UINT8 ReservedBits: 7; // Reserved bit fields for padding. > UINT16 BitOneof : 6; >+ UINT16 : 0; // Width 0 used to force alignment. > UINT16 BitNumeric : 12; > MY_BITS_DATA MyBitData; > MY_EFI_UNION_DATA MyUnionData; > } DRIVER_SAMPLE_CONFIGURATION; > >@@ -107,10 +117,11 @@ typedef struct { > MY_BITS_DATA BitsData; > UINT32 EfiBitGrayoutTest : 5; > UINT32 EfiBitNumeric : 4; > UINT32 EfiBitOneof : 10; > UINT32 EfiBitCheckbox : 1; >+ UINT32 : 0; // Width 0 used to force alignment. > } MY_EFI_BITS_VARSTORE_DATA; > > // > // Labels definition > // >-- >1.9.5.msysgit.1
_______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel