[CHERRY-PICK] MdePkg/BaseLib: Add AsmReadFsBase and AsmWriteFsBase for X86-64

[Gowtham-Manikandan]

Description

The commit that adds Asm(Read|Write)FsBase to BaseLib for x86-64.
(cherry picked from commit e2b0e207f7b1009a6729f7973ed17242cb6672a4)

• Impacts functionality?
• Impacts security?
• Breaking change?
• Includes tests?
• Includes documentation?

How This Was Tested

Call AsmWriteFsBase() and use AsmReadFsBase() to check if the value is written to FSBASE.

Integration Instructions

N/A

[mu-automation]

✅ QEMU Validation Passed

Source Dependencies

Repository	Commit
mu_basecore	95e7870
mu_tiano_platforms	274d484

Results

Platform	Target	Build	Boot	Overall Boot Time	Build Logs	Boot Logs
Q35	DEBUG	✅ success	✅ success	0m 17s	Build Logs	Boot Logs
SBSA	DEBUG	✅ success	✅ success	0m 34s	Build Logs	Boot Logs

Workflow run: https://github.com/microsoft/mu_basecore/actions/runs/26307549638

This comment was automatically generated by the Mu QEMU PR Validation workflow.

[Gowtham-Manikandan]

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 0% with 39 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/202511@1800e61). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
MdePkg/Library/BaseLib/X64/FsGsBase.c	0.00%	39 Missing ⚠️

Additional details and impacted files

@@                Coverage Diff                @@
##             release/202511    #1804   +/-   ##
=================================================
  Coverage                  ?    2.21%           
=================================================
  Files                     ?     1634           
  Lines                     ?   420108           
  Branches                  ?     4949           
=================================================
  Hits                      ?     9308           
  Misses                    ?   410725           
  Partials                  ?       75           

Flag	Coverage Δ
FmpDevicePkg	9.53% <ø> (?)
MdeModulePkg	1.58% <ø> (?)
MdePkg	5.44% <0.00%> (?)
NetworkPkg	0.55% <ø> (?)
PolicyServicePkg	30.42% <ø> (?)
SecurityPkg	1.59% <ø> (?)
UefiCpuPkg	4.78% <ø> (?)
UnitTestFrameworkPkg	11.70% <ø> (?)

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[os-d]

The edk2 commit message is empty for this one, so I'm fine to just do a squash on this and take the cherry-pick name and the commit hash in the PR description.

Usually, we would do git cherry-pick -x <hash>, then amend the commit to add [CHERRY-PICK] to the title so we retain the edk2 commit information but still know for ourselves it was a cherry-pick.

[makubacki]

The edk2 commit message is empty for this one, so I'm fine to just do a squash on this and take the cherry-pick name and the commit hash in the PR description.

Usually, we would do git cherry-pick -x <hash>, then amend the commit to add [CHERRY-PICK] to the title so we retain the edk2 commit information but still know for ourselves it was a cherry-pick.

I don't think we'll preserve the author in the squash. If we can change it back to Ray, fine. Otherwise, it'd be more consistent to at the -x line to the empty commit message and preserve the author/committer appropriately.

[makubacki]

Note: Current SBSA boot failure is due to a recent, unrelated change.

[makubacki]

@Gowtham-Manikandan, thanks for repushing so the author was correct. The Signed-off-by line and the cherry-pick -x line were still missing from the commit message, so I pushed that update to your PR branch. I've set automerge for the PR as well.