On 07/23/14 13:34, Varad Gautam wrote:
Hi, I am working on the BeagleBoneBlack port for EDK2 and am facing an issue with PcdGet(): it always returns `0` no matter what the PCD is set to. However, FixedPcdGet() works fine (I've had to patch edk2 to replace all PcdGet calls with FixedPcdGet to get PrePi working which is a bad idea).
The build report too shows the PCDs being set to their proper values, and so do the AutoGen.i file macros like `const UINT32 _gPcd_FixedAtBuild_PcdFvBaseAddress = 0x80008000U;`
I've come up with two reasons to this,
- Is there a build flag I'm missing to enable PcdGet support?
- `_gPcd_FixedAtBuild_PcdFvBaseAddress` is declared with
`GLOBAL_REMOVE_IF_UNREFERENCED` in AutoGen.c and gets removed before I can use it. This also explains why FixedPcdGet would work, since `_PCD_VALUE_PcdFvBaseAddress` is correctly #defined to be 0x80008000U.
This happens for all fixed-at-build type PCDs. Also, I'm linked to PcdLib|MdePkg/Library/BasePcdLibNull/BasePcdLibNull.inf for the buid. What could I try to fix it?
You're getting this result because you're combining incorrect library class resolution with RELEASE builds. (I cannot condemn RELEASE builds enough.) Namely, you call
UINT32 EFIAPI LibPcdGet32 ( IN UINTN TokenNumber ) { ASSERT (FALSE);
return 0; }
from "MdePkg/Library/BasePcdLibNull/PcdLib.c", and since you build for RELEASE, the ASSERT() is a no-op. In a DEBUG build you'd have caught this immediately with a failed assertion: the Null implementation of PcdLib doesn't allow you to actually access PCDs.
Library instances that usably resolve the PcdLib library class are:
$ git grep -l 'LIBRARY_CLASS *= *PcdLib' -- '*.inf'
EmulatorPkg/Library/SmbiosLib/SmbiosLib.inf MdePkg/Library/BasePcdLibNull/BasePcdLibNull.inf MdePkg/Library/DxePcdLib/DxePcdLib.inf MdePkg/Library/PeiPcdLib/PeiPcdLib.inf
In PEIMs, you need the fourth; in DXE & UEFI drivers, you need the third.
However, this is not the entire picture yet, because these libraries delegate the work to a PPI (in PEI) and to a protocol (in DXE) that are provided by dedicated drivers, respectively: - MdeModulePkg/Universal/PCD/Pei/Pcd.inf - MdeModulePkg/Universal/PCD/Dxe/Pcd.inf
You should add these drivers to the corresponding (ie. PEI vs. DXE) APRIORI files of the firmware volumes that your FDF file defines, so that any driver loaded / dispatched later can use their PCD services (through the above-mentioned library instances). Refer to OvmfPkg/OvmfPkgX64.fdf for examples.
Thanks Laszlo