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diff --git a/Lessons/Lesson_23/README.md b/Lessons/Lesson_23/README.md new file mode 100644 index 0000000..bae429d --- /dev/null +++ b/Lessons/Lesson_23/README.md @@ -0,0 +1,225 @@ +Now let's explore `PatchableInModule` PCD. + +Add PCD to DEC file UefiLessonsPkg/UefiLessonsPkg.dec: +``` +[PcdsPatchableInModule] + gUefiLessonsPkgTokenSpaceGuid.PcdMyPatchableVar32|0x31313131|UINT32|0x00000004 +``` +Populate it to INF UefiLessonsPkg/PCDLesson/PCDLesson.inf: +``` +[PatchPcd] + gUefiLessonsPkgTokenSpaceGuid.PcdMyPatchableVar32 +``` + +To get a value of PCD in a *.c file either `PatchPcdGet` or generic `PcdGet` should be used. + +Let's test both methods: +``` +Print(L"PcdMyPatchableVar32=%d\n", PatchPcdGet32(PcdMyPatchableVar32)); +Print(L"PcdMyPatchableVar32=%d\n", PcdGet32(PcdMyPatchableVar32)); +``` + +Now build and look to AutoGen files: + +Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/AutoGen.h +``` +#define _PCD_TOKEN_PcdMyPatchableVar32 0U +#define _PCD_PATCHABLE_VALUE_PcdMyPatchableVar32 ((UINT32)0x31313131U) +extern volatile UINT32 _gPcd_BinaryPatch_PcdMyPatchableVar32; +#define _PCD_GET_MODE_32_PcdMyPatchableVar32 _gPcd_BinaryPatch_PcdMyPatchableVar32 +#define _PCD_PATCHABLE_PcdMyPatchableVar32_SIZE 4 +#define _PCD_GET_MODE_SIZE_PcdMyPatchableVar32 _gPcd_BinaryPatch_Size_PcdMyPatchableVar32 +extern UINTN _gPcd_BinaryPatch_Size_PcdMyPatchableVar32; +#define _PCD_SET_MODE_32_PcdMyPatchableVar32(Value) (_gPcd_BinaryPatch_PcdMyPatchableVar32 = (Value)) +#define _PCD_SET_MODE_32_S_PcdMyPatchableVar32(Value) ((_gPcd_BinaryPatch_PcdMyPatchableVar32 = (Value)), RETURN_SUCCESS) +``` +Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/AutoGen.c +``` +volatile UINT32 _gPcd_BinaryPatch_PcdMyPatchableVar32 = _PCD_PATCHABLE_VALUE_PcdMyPatchableVar32; +GLOBAL_REMOVE_IF_UNREFERENCED UINTN _gPcd_BinaryPatch_Size_PcdMyPatchableVar32 = 4; +``` + +So in this case our call to `PcdGet32(PcdMyPatchableVar32)` would be expanded to: +``` +PcdGet32(PcdMyPatchableVar32) --> _PCD_GET_MODE_32_PcdMyPatchableVar32 --> _gPcd_BinaryPatch_PcdMyPatchableVar32 +``` +This variable would be assigned in `AutoGen.c`: +``` +volatile UINT32 _gPcd_BinaryPatch_PcdMyPatchableVar32 = ((UINT32)0x31313131U); +``` +So the main difference from the FixedAtBuild and FeatureFlag PCDs is that variable defined as `volatile` and set functions aren't blocked. + +Let's try to set our PCD then. As with get, there are two possibilities. You can use either `PatchPcdSet<Type>` or generic `PcdSet<Type>S`. + +Keep in mind that `PcdSet32S` unravels to a macro returning a value. +https://github.com/tianocore/edk2/blob/master/MdePkg/Include/Library/PcdLib.h: +``` +#define PcdSet32S(TokenName, Value) _PCD_SET_MODE_32_S_##TokenName ((Value)) +``` +Therefore: +``` +PcdSet32S(PcdMyPatchableVar32, 44) --> _PCD_SET_MODE_32_S_PcdMyPatchableVar32 ((Value)) --> ((_gPcd_BinaryPatch_PcdMyPatchableVar32 = (Value)), RETURN_SUCCESS) +``` + +So if you don't want such error: +``` +/home/kostr/tiano/edk2/Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/AutoGen.h:108:106: error: right-hand operand of comma expression has no effect [-Werror=unused-value] + 108 | #define _PCD_SET_MODE_32_S_PcdMyPatchableVar32(Value) ((_gPcd_BinaryPatch_PcdMyPatchableVar32 = (Value)), RETURN_SUCCESS) + | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~. +``` +You should use something like this: +``` +RETURN_STATUS PcdStatus = PcdSet32S(PcdMyPatchableVar32, 44); +Print(L"PcdStatus=%r\n", PcdStatus); +``` + +Alternatively you can use `PatchPcdSet32` which don't require such thing as it is defined as follows: +``` +#define PatchPcdSet32(TokenName, Value) (_gPcd_BinaryPatch_##TokenName = (Value)) +``` + +Test both set methods in app code: +``` +Print(L"PcdMyPatchableVar32=0x%x\n", PcdGet32(PcdMyPatchableVar32)); +RETURN_STATUS PcdStatus = PcdSet32S(PcdMyPatchableVar32, 44); +Print(L"PcdStatus=%r\n", PcdStatus); +Print(L"PcdMyPatchableVar32=%d\n", PcdGet32(PcdMyPatchableVar32)); +PatchPcdSet32(PcdMyPatchableVar32, 45); +Print(L"PcdMyPatchableVar32=%d\n", PatchPcdGet32(PcdMyPatchableVar32)); +``` + + +Now if you execute our app under OVMF prints for patchable PCDs would output: +``` +PcdMyPatchableVar32=0x31313131 +PcdStatus=Success +PcdMyPatchableVar32=44 +PcdMyPatchableVar32=45 +``` + +_________________________________ + +In case you've wondered why I've assigned a hex value for PCD default value or why this PCD type is named `PatchableInModule` this section is for you. + +This PCD type is named like that because the value of this PCD can be changed in a binary PE/COFF image (*.efi file). To do this two utilities are used: +- `GenPatchPcdTable` - this tool is used to get the patchable PCD offset for the EFI image by parsing the map file +- `PatchPcdValue` - this tool is used to actually patch PCD value + +You can download rtf manuals for these utilities from edk2 repo: +-https://github.com/tianocore/edk2/blob/master/BaseTools/UserManuals/GenPatchPcdTable_Utility_Man_Page.rtf +-https://github.com/tianocore/edk2/blob/master/BaseTools/UserManuals/PatchPcdValue_Utility_Man_Page.rtf + +Let's start with `GenPatchPcdTable`. First check out help for this tool: +``` +$ ./BaseTools/BinWrappers/PosixLike/GenPatchPcdTable -h +Usage: GenPatchPcdTable.py -m <MapFile> -e <EfiFile> -o <OutFile> + +Copyright (c) 2008 - 2018, Intel Corporation. All rights reserved. + +Options: + --version show program's version number and exit + -h, --help show this help message and exit + -m MAPFILE, --mapfile=MAPFILE + Absolute path of module map file. + -e EFIFILE, --efifile=EFIFILE + Absolute path of EFI binary file. + -o OUTFILE, --outputfile=OUTFILE + Absolute path of output file to store the got + patchable PCD table. +``` +Now let's create a `PatchPcdTable` for our app: + +For the *.efi file we can use one of: +``` +Build/UefiLessonsPkg/RELEASE_GCC5/X64/PCDLesson.efi +Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/OUTPUT/PCDLesson.efi +Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.efi +``` +For the *.map file we can use one of: +``` +Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.map +Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/OUTPUT/PCDLesson.map +``` +In case you wonder how our PCD can be found in a map file, execute: +``` +$ grep MyPatchableVar32 Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.map -A2 + .data._gPcd_BinaryPatch_PcdMyPatchableVar32 + 0x0000000000001920 0x4 /tmp/PCDLesson.dll.m6t8YL.ltrans0.ltrans.o + *fill* 0x0000000000001924 0xc +``` +So as you can see the default value for our PCD is placed under 0x1920 offset. + +Now let's execute `GenPatchPcdTable` and create a file `PCDLessonPatchPcdTable` in app Build DEBUG folder: +``` +./BaseTools/BinWrappers/PosixLike/GenPatchPcdTable \ + -m Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.map \ + -e Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.efi \ + -o Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLessonPatchPcdTable +``` + +Checkout the created `PCDLessonPatchPcdTable` file. +``` +$ cat Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLessonPatchPcdTable +PCD Name Offset Section Name +PcdMyPatchableVar32 0x1920 .data +``` +As you can see it has the same offset that we've seen in a map file. + +Now let's get a final look at our default PCD value in an *.elf file: +``` +hexdump -s 0x1920 Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.efi -n 4 +0001920 3131 3131 +0001924 +``` + +Checkout help for the `PatchPcdValue` tool: +``` +$ ./BaseTools/BinWrappers/PosixLike/PatchPcdValue -h +Usage: PatchPcdValue.py -f Offset -u Value -t Type [-s MaxSize] <input_file> + +Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved. + +Options: + -f PCDOFFSET, --offset=PCDOFFSET + Start offset to the image is used to store PCD value. + -u PCDVALUE, --value=PCDVALUE + PCD value will be updated into the image. + -t PCDTYPENAME, --type=PCDTYPENAME + The name of PCD data type may be one of VOID*,BOOLEAN, + UINT8, UINT16, UINT32, UINT64. + -s PCDMAXSIZE, --maxsize=PCDMAXSIZE + Max size of data buffer is taken by PCD value.It must + be set when PCD type is VOID*. + -v, --verbose Run verbosely + -d LOGLEVEL, --debug=LOGLEVEL + Run with debug information + -q, --quiet Run quietly + -? show this help message and exit + --version show program's version number and exit + -h, --help show this help message and exit +``` + +Now use it to patch our PCD in an *.elf file: +``` +./BaseTools/BinWrappers/PosixLike/PatchPcdValue \ + --offset=0x1920 \ + --value=0xDEADDEAD \ + --type=UINT32 \ + Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.efi +``` +Look at hexdump again: +``` +$ hexdump -s 0x1920 Build/UefiLessonsPkg/RELEASE_GCC5/X64/UefiLessonsPkg/PCDLesson/PCDLesson/DEBUG/PCDLesson.efi -n 4 +0001920 dead dead +0001924 +``` +We've successfully changed our PCD in a binary! + +Now if you execute our app under OVMF prints for patchable PCDs would output: +``` +PcdMyPatchableVar32=0xDEADDEAD +PcdStatus=Success +PcdMyPatchableVar32=44 +PcdMyPatchableVar32=45 +``` + |