Difference between boolean PCD fixed at build and a PCD feature flag


Konstantin Aladyshev <aladyshev22@...>
 

What is the difference between boolean PCD fixed at build and a PCD feature flag?
```
[PcdsFixedAtBuild]
  gMyPkgTokenSpaceGuid.PcdMyVarBool|FALSE|BOOLEAN|0x00000004

[PcdsFeatureFlag]
  gMyPkgTokenSpaceGuid.PcdMyFeatureFlagVar|FALSE|BOOLEAN|0x20000001
```
I'm looking at the AutoGen files and the result from both of these PCDs is practically the same.

AutoGen.c
```
GLOBAL_REMOVE_IF_UNREFERENCED const BOOLEAN _gPcd_FixedAtBuild_PcdMyVarBool = _PCD_VALUE_PcdMyVarBool;
GLOBAL_REMOVE_IF_UNREFERENCED const BOOLEAN _gPcd_FixedAtBuild_PcdMyFeatureFlagVar = _PCD_VALUE_PcdMyFeatureFlagVar;
```
AutoGen.h
```
#define _PCD_TOKEN_PcdMyVarBool  0U
#define _PCD_SIZE_PcdMyVarBool 1
#define _PCD_GET_MODE_SIZE_PcdMyVarBool  _PCD_SIZE_PcdMyVarBool
#define _PCD_VALUE_PcdMyVarBool  0U
extern const  BOOLEAN  _gPcd_FixedAtBuild_PcdMyVarBool;
#define _PCD_GET_MODE_BOOL_PcdMyVarBool  _gPcd_FixedAtBuild_PcdMyVarBool
//#define _PCD_SET_MODE_BOOL_PcdMyVarBool  ASSERT(FALSE)  // It is not allowed to set value for a FIXED_AT_BUILD PCD

#define _PCD_TOKEN_PcdMyFeatureFlagVar  0U
#define _PCD_SIZE_PcdMyFeatureFlagVar 1
#define _PCD_GET_MODE_SIZE_PcdMyFeatureFlagVar  _PCD_SIZE_PcdMyFeatureFlagVar
#define _PCD_VALUE_PcdMyFeatureFlagVar  ((BOOLEAN)0U)
extern const  BOOLEAN  _gPcd_FixedAtBuild_PcdMyFeatureFlagVar;
#define _PCD_GET_MODE_BOOL_PcdMyFeatureFlagVar  _gPcd_FixedAtBuild_PcdMyFeatureFlagVar
//#define _PCD_SET_MODE_BOOL_PcdMyFeatureFlagVar  ASSERT(FALSE)  // It is not allowed to set value for a FIXED_AT_BUILD PCD
```

Are there any actual differences between those two methods of defining a PCD? Or is `PcdsFeatureFlag` simply a syntactic sugar?

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