[scudo] Change CompactPtrT and CompactPtrScale to optional

[ChiaHungDuan]

No description provided.

[llvmbot]

@llvm/pr-subscribers-compiler-rt-sanitizer

Author: None (ChiaHungDuan)

Changes

---

Full diff: https://github.com/llvm/llvm-project/pull/90797.diff

1 Files Affected:

• (modified) compiler-rt/lib/scudo/standalone/allocator_config.def (+8-8)

diff --git a/compiler-rt/lib/scudo/standalone/allocator_config.def b/compiler-rt/lib/scudo/standalone/allocator_config.def
index dcd130ac449a0a..ce37b1cfaedccc 100644
--- a/compiler-rt/lib/scudo/standalone/allocator_config.def
+++ b/compiler-rt/lib/scudo/standalone/allocator_config.def
@@ -56,16 +56,8 @@ BASE_OPTIONAL(const bool, MaySupportMemoryTagging, false)
 // SizeClassMap to use with the Primary.
 PRIMARY_REQUIRED_TYPE(SizeClassMap)
 
-// Defines the type and scale of a compact pointer. A compact pointer can
-// be understood as the offset of a pointer within the region it belongs
-// to, in increments of a power-of-2 scale. See `CompactPtrScale` also.
-PRIMARY_REQUIRED_TYPE(CompactPtrT)
-
 // PRIMARY_REQUIRED(TYPE, NAME)
 //
-// The scale of a compact pointer. E.g., Ptr = Base + (CompactPtr << Scale).
-PRIMARY_REQUIRED(const uptr, CompactPtrScale)
-
 // Log2 of the size of a size class region, as used by the Primary.
 PRIMARY_REQUIRED(const uptr, RegionSizeLog)
 
@@ -86,6 +78,9 @@ PRIMARY_REQUIRED(const s32, MaxReleaseToOsIntervalMs)
 
 // PRIMARY_OPTIONAL(TYPE, NAME, DEFAULT)
 //
+// The scale of a compact pointer. E.g., Ptr = Base + (CompactPtr << Scale).
+PRIMARY_OPTIONAL(const uptr, CompactPtrScale, SCUDO_MIN_ALIGNMENT_LOG)
+
 // Indicates support for offsetting the start of a region by a random number of
 // pages. This is only used if `EnableContiguousRegions` is enabled.
 PRIMARY_OPTIONAL(const bool, EnableRandomOffset, false)
@@ -104,6 +99,11 @@ PRIMARY_OPTIONAL(const bool, EnableContiguousRegions, true)
 // guarantee a performance benefit.
 PRIMARY_OPTIONAL_TYPE(ConditionVariableT, ConditionVariableDummy)
 
+// Defines the type and scale of a compact pointer. A compact pointer can
+// be understood as the offset of a pointer within the region it belongs
+// to, in increments of a power-of-2 scale. See `CompactPtrScale` also.
+PRIMARY_OPTIONAL_TYPE(CompactPtrT, uptr)
+
 // SECONDARY_REQUIRED_TEMPLATE_TYPE(NAME)
 //
 // Defines the type of Secondary Cache to use.

[ChiaHungDuan]

Add more context, given that primary32 doesn't do pointer compaction, make them optional. This is one of the CLs to deprecate primary32.

[cferris1000]

LGTM.

[fabio-d]

Defines ... and scale -> the scale is actually defined by CompactPtrScale

I think it might help here to document how to choose the proper type, for instance

This type is used to efficiently store arrays of pointers to free blocks, and it must be large enough to express offsets within an entire region, i.e. this type's maximum possible value must uphold MaxCompactPtrValue << CompactPtrScale >= 1 << RegionSizeLog. The default type (uptr) trivially satisfies this requirement but, depending on CompactPtrScale and RegionSizeLog, a smaller type could work too.