Memory leak !?

[anandhkrishna]

why we didn't free the hob memory here , since the Hobs are moved to system memory here

[r1chard-lyu]

I’m interested in this topic as well and look forward to seeing more discussion.

[os-d]

@anandhkrishna @r1chard-lyu , I believe the answer here is that this is not a memory leak because the HOB list itself is not covered in a memory allocation HOB, so DXE Core does not see it as allocated memory, but part of free memory. That is why it must be relocated and tracked as allocated memory in DXE, so that it is not stomped on. See

edk2/MdeModulePkg/Core/Pei/Hob/Hob.c

Lines 104 to 116 in bff5093

	*Hob = (VOID *)(UINTN)HandOffHob->EfiEndOfHobList;
	((EFI_HOB_GENERIC_HEADER *)*Hob)->HobType = Type;
	((EFI_HOB_GENERIC_HEADER *)*Hob)->HobLength = Length;
	((EFI_HOB_GENERIC_HEADER *)*Hob)->Reserved = 0;
	HobEnd = (EFI_HOB_GENERIC_HEADER *)((UINTN)*Hob + Length);
	HandOffHob->EfiEndOfHobList = (EFI_PHYSICAL_ADDRESS)(UINTN)HobEnd;
	HobEnd->HobType = EFI_HOB_TYPE_END_OF_HOB_LIST;
	HobEnd->HobLength = (UINT16)sizeof (EFI_HOB_GENERIC_HEADER);
	HobEnd->Reserved = 0;
	HobEnd++;
	HandOffHob->EfiFreeMemoryBottom = (EFI_PHYSICAL_ADDRESS)(UINTN)HobEnd;

and the comment here:

edk2/MdeModulePkg/Core/Dxe/Gcd/Gcd.c

Lines 2841 to 2845 in 5158b59

	// Relocate HOB List to an allocated pool buffer.
	// The relocation should be at after all the tested memory resources added
	// (except the memory space that covers HOB List) to the memory services,
	// because the memory resource found in CoreInitializeMemoryServices()
	// may have not enough remaining resource for HOB List.

.

[r1chard-lyu]

@os-d Thank you for the detailed explanation. I understand now!