[llvm][AddressSanitizer] option for specifying the address space of the shadow map

[etsal]

The AddressSanitizer transform currently defaults to placing the shadow map in address space 0, but it is desirable for some targets (namely BPF) to select a different address space for the map. Add a compilation option for specifying the address space of the target.

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[llvmbot]

@llvm/pr-subscribers-llvm-transforms

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

Author: Emil Tsalapatis (etsal)

Changes

The AddressSanitizer transform currently defaults to placing the shadow map in address space 0, but it is desirable for some targets (namely BPF) to select a different address space for the map. Add a compilation option for specifying the address space of the target.

---

Full diff: https://github.com/llvm/llvm-project/pull/167772.diff

1 Files Affected:

• (modified) llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp (+6-1)

diff --git a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
index 7c364f86fb0e8..8d3b712553c6d 100644
--- a/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
+++ b/llvm/lib/Transforms/Instrumentation/AddressSanitizer.cpp
@@ -248,6 +248,11 @@ static cl::opt<bool>
                          "platforms that support this"),
                 cl::Hidden, cl::init(true));
 
+static cl::opt<int>
+    ClShadowASpace("asan-shadow-aspace",
+                cl::desc("Address space for pointers to the shadow map"),
+                cl::Hidden, cl::init(0));
+
 static cl::opt<bool> ClWithIfuncSuppressRemat(
     "asan-with-ifunc-suppress-remat",
     cl::desc("Suppress rematerialization of dynamic shadow address by passing "
@@ -1942,7 +1947,7 @@ void AddressSanitizer::instrumentAddress(Instruction *OrigIns,
 
   Type *ShadowTy =
       IntegerType::get(*C, std::max(8U, TypeStoreSize >> Mapping.Scale));
-  Type *ShadowPtrTy = PointerType::get(*C, 0);
+  Type *ShadowPtrTy = PointerType::get(*C, ClShadowASpace);
   Value *ShadowPtr = memToShadow(AddrLong, IRB);
   const uint64_t ShadowAlign =
       std::max<uint64_t>(Alignment.valueOrOne().value() >> Mapping.Scale, 1);

[thurstond]

Nit: "aspace" is too terse. Please expand it to address-space, or at least addr-space.

[etsal]

Sounds good, will update. I assume you mean the command line option and not the C++ side variable, if not I can change that too.

[thurstond]

Please change both: for consistency, and also because "A" is not typically used as shorthand for Address in the variable names. For example, immediately after ClShadowASpace, we have AddrLong (not "ALong"):

  Type *ShadowPtrTy = PointerType::get(*C, ClShadowASpace);
  Value *ShadowPtr = memToShadow(AddrLong, IRB);

[etsal]

Makes sense, I used ASpace because that's the shorthand used in Target/BPF and I did not register the fact it's different in the sanitizer passes.

[thurstond]

Ah, I see! TIL :-)

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[etsal]

Hi, I just realized I have to explicitly ask for this to get merged. Can we merge this and the other 3 Accepted PRs related to AddressSanitizer & BPF?

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[thurstond]

Hi, I just realized I have to explicitly ask for this to get merged. Can we merge this and the other 3 Accepted PRs related to AddressSanitizer & BPF?

Thanks for the all fixes! I've merged three of the PRs; for the fourth PR in the series (#167770), I've enabled auto-merge (it will merge once CI completes). Sorry for the delay.

[etsal]

No worries, thanks for the (very) quick response!