Re: [edk2-devel] [PATCH] UefiCpuPkg/CpuPageTableLib: qualify page table accesses as volatile

[Michael Brown]

On 22/02/2024 08:41, Zhou Jianfeng wrote:
--- a/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
+++ b/UefiCpuPkg/Library/CpuPageTableLib/CpuPageTableMap.c
@@ -20,13 +20,13 @@
  **/
  VOID
  PageTableLibSetPte4K (
-  IN OUT IA32_PTE_4K         *Pte4K,
-  IN UINT64                  Offset,
-  IN IA32_MAP_ATTRIBUTE      *Attribute,
-  IN IA32_MAP_ATTRIBUTE      *Mask
+  IN OUT volatile IA32_PTE_4K  *Pte4K,
+  IN UINT64                    Offset,
+  IN IA32_MAP_ATTRIBUTE        *Attribute,
+  IN IA32_MAP_ATTRIBUTE        *Mask
    )
  {
-  IA32_PTE_4K  LocalPte4K;
+  volatile IA32_PTE_4K  LocalPte4K;

While it may well cause the compiler to generate less optimised code, 
there is absolutely no way that this volatile declaration on a local 
stack variable can possibly change the outcome of the code.

There can never be any meaningful side-effects from reading or writing a 
stack variable.

I would suggest dropping the volatile on LocalPte4K, since its *only* 
possible impact is to confuse a future reader of the code.

-  IA32_PAGE_LEAF_ENTRY_BIG_PAGESIZE  LocalPleB;
+  volatile IA32_PAGE_LEAF_ENTRY_BIG_PAGESIZE  LocalPleB;

Same comment.

-  IA32_PAGE_NON_LEAF_ENTRY  LocalPnle;
+  volatile IA32_PAGE_NON_LEAF_ENTRY  LocalPnle;

Same comment.

Thanks,

Michael



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