[PATCH] D72994: [Sema] Sanitize alignment requested via `__attribute__((assume_aligned(imm)))`

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: erichkeane, aaron.ballman, hfinkel, rsmith, jdoerfert.
lebedev.ri added a project: LLVM.
Herald added a project: clang.
Herald added a subscriber: cfe-commits.
lebedev.ri added a parent revision: D72993: [NFC][Codegen] Use MaybeAlign + APInt::getLimitedValue() when creating Alignment attr.

For `__builtin_assume_aligned()`, we do validate that the alignment
is not greater than `536870912` (D68824 <https://reviews.llvm.org/D68824>), but we don't do that for
`__attribute__((assume_aligned(N)))` attribute.
I suspect we should.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D72994

Files:
  clang/lib/Sema/SemaDeclAttr.cpp
  clang/test/Sema/builtin-assume-aligned.c


Index: clang/test/Sema/builtin-assume-aligned.c
===================================================================
--- clang/test/Sema/builtin-assume-aligned.c
+++ clang/test/Sema/builtin-assume-aligned.c
@@ -46,6 +46,7 @@
 void test_void_assume_aligned(void) __attribute__((assume_aligned(32))); // expected-warning {{'assume_aligned' attribute only applies to return values that are pointers}}
 int test_int_assume_aligned(void) __attribute__((assume_aligned(16))); // expected-warning {{'assume_aligned' attribute only applies to return values that are pointers}}
 void *test_ptr_assume_aligned(void) __attribute__((assume_aligned(64))); // no-warning
+void *test_ptr_assume_aligned(void) __attribute__((assume_aligned(1073741824))); // expected-warning {{requested alignment must be 536870912 bytes or smaller; maximum alignment assumed}}
 
 int j __attribute__((assume_aligned(8))); // expected-warning {{'assume_aligned' attribute only applies to Objective-C methods and functions}}
 void *test_no_fn_proto() __attribute__((assume_aligned(32))); // no-warning
Index: clang/lib/Sema/SemaDeclAttr.cpp
===================================================================
--- clang/lib/Sema/SemaDeclAttr.cpp
+++ clang/lib/Sema/SemaDeclAttr.cpp
@@ -1625,6 +1625,12 @@
         << E->getSourceRange();
       return;
     }
+
+    // Alignment calculations can wrap around if it's greater than 2**29.
+    unsigned MaximumAlignment = 536870912;
+    if (I > MaximumAlignment)
+      Diag(CI.getLoc(), diag::warn_assume_aligned_too_great)
+          << CI.getRange() << MaximumAlignment;
   }
 
   if (OE) {


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