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DynamicTablesPkg: Helper function to compute package length 

Some AML object have a PkgLen which indicates the size of the
AML object. The package length can be encoded in 1 to 4 bytes.
The bytes used to encode the PkgLen is itself counted in the
PkgLen value. So, if an AML object's size increments/decrements,
the number of bytes used to encode the PkgLen value can itself
increment/decrement.

Therefore, a helper function AmlComputePkgLength() is introduced
to simply computation of the PkgLen.

Reviewed-by: Sami Mujawar <sami.mujawar@arm.com>
Signed-off-by: Pierre Gondois <Pierre.Gondois@arm.com>
This commit is contained in:
Pierre Gondois 2021-10-08 15:46:24 +01:00 committed by mergify[bot]
parent 1e33479b39
commit 12e65fd258
2 changed files with 132 additions and 2 deletions
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87
DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.c
View File

@ -2,7 +2,7 @@
AML grammar definitions.
Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved. <BR>
Copyright (c) 2019 - 2020, Arm Limited. All rights reserved.<BR>
Copyright (c) 2019 - 2021, Arm Limited. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
@ -803,3 +803,88 @@ AmlComputePkgLengthWidth (
// Length < 2^6
return 1;
}
/** Given a length, compute the value of a PkgLen.
In AML, some object have a PkgLen, telling the size of the AML object.
It can be encoded in 1 to 4 bytes. The bytes used to encode the PkgLen is
itself counted in the PkgLen value.
This means that if an AML object sees its size increment/decrement,
the number of bytes used to encode the PkgLen value can itself
increment/decrement.
For instance, the AML encoding of a DeviceOp is:
DefDevice := DeviceOp PkgLength NameString TermList
If:
- sizeof (NameString) = 4 (the name is "DEV0" for instance);
- sizeof (TermList) = (2^6-6)
then the PkgLen is encoded on 1 byte. Indeed, its value is:
sizeof (PkgLen) + sizeof (NameString) + sizeof (TermList) =
sizeof (PkgLen) + 4 + (2^6-6)
So:
PkgLen = sizeof (PkgLen) + (2^6-2)
The input arguments Length and PkgLen represent, for the DefDevice:
DefDevice := DeviceOp PkgLength NameString TermList
|------Length-----|
|--------*PgkLength---------|
@param [in] Length The length to encode as a PkgLen.
Length cannot exceed 2^28 - 4 (4 bytes for the
PkgLen encoding).
The size of the PkgLen encoding bytes should not be
counted in this length value.
@param [out] PkgLen If success, contains the value of the PkgLen,
ready to encode in the PkgLen format.
This value takes into account the size of PkgLen
encoding.
@retval EFI_SUCCESS The function completed successfully.
@retval EFI_INVALID_PARAMETER Invalid parameter.
**/
EFI_STATUS
EFIAPI
AmlComputePkgLength (
IN UINT32 Length,
OUT UINT32 * PkgLen
)
{
UINT32 PkgLenWidth;
UINT32 ReComputedPkgLenWidth;
if (PkgLen == NULL) {
ASSERT (0);
return EFI_INVALID_PARAMETER;
}
// Compute the PkgLenWidth.
PkgLenWidth = AmlComputePkgLengthWidth (Length);
if (PkgLenWidth == 0) {
ASSERT (0);
return EFI_INVALID_PARAMETER;
}
// Add it to the Length.
Length += PkgLenWidth;
// Check that adding the PkgLenWidth didn't trigger a domino effect,
// increasing the encoding width of the PkgLen again.
// The PkgLen is encoded in at most 4 bytes. It is possible to increase
// the PkgLen width if its encoding is less than 3 bytes.
ReComputedPkgLenWidth = AmlComputePkgLengthWidth (Length);
if (ReComputedPkgLenWidth != PkgLenWidth) {
if ((ReComputedPkgLenWidth != 0) &&
(ReComputedPkgLenWidth < 4)) {
// No need to recompute the PkgLen since a new threshold cannot
// be reached by incrementing the value by one.
Length += 1;
} else {
ASSERT (0);
return EFI_INVALID_PARAMETER;
}
}
*PkgLen = Length;
return EFI_SUCCESS;
}

47
DynamicTablesPkg/Library/Common/AmlLib/AmlEncoding/Aml.h
View File

@ -2,7 +2,7 @@
AML grammar definitions.
Copyright (c) 2010 - 2018, Intel Corporation. All rights reserved. <BR>
Copyright (c) 2019 - 2020, Arm Limited. All rights reserved.<BR>
Copyright (c) 2019 - 2021, Arm Limited. All rights reserved.<BR>
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
@ -326,5 +326,50 @@ AmlComputePkgLengthWidth (
IN UINT32 Length
);
/** Given a length, compute the value of a PkgLen.
In AML, some object have a PkgLen, telling the size of the AML object.
It can be encoded in 1 to 4 bytes. The bytes used to encode the PkgLen is
itself counted in the PkgLen value.
This means that if an AML object sees its size increment/decrement,
the number of bytes used to encode the PkgLen value can itself
increment/decrement.
For instance, the AML encoding of a DeviceOp is:
DefDevice := DeviceOp PkgLength NameString TermList
If:
- sizeof (NameString) = 4 (the name is "DEV0" for instance);
- sizeof (TermList) = (2^6-6)
then the PkgLen is encoded on 1 byte. Indeed, its value is:
sizeof (PkgLen) + sizeof (NameString) + sizeof (TermList) =
sizeof (PkgLen) + 4 + (2^6-6)
So:
PkgLen = sizeof (PkgLen) + (2^6-2)
The input arguments Length and PkgLen represent, for the DefDevice:
DefDevice := DeviceOp PkgLength NameString TermList
|------Length-----|
|--------*PgkLength---------|
@param [in] Length The length to encode as a PkgLen.
Length cannot exceed 2^28 - 4 (4 bytes for the
PkgLen encoding).
The size of the PkgLen encoding bytes should not be
counted in this length value.
@param [out] PkgLen If success, contains the value of the PkgLen,
ready to encode in the PkgLen format.
This value takes into account the size of PkgLen
encoding.
@retval EFI_SUCCESS The function completed successfully.
@retval EFI_INVALID_PARAMETER Invalid parameter.
**/
EFI_STATUS
EFIAPI
AmlComputePkgLength (
IN UINT32 Length,
OUT UINT32 * PkgLen
);
#endif // AML_H_