From bd1c0870198e025f92d31eead0fb2019c4057a4a Mon Sep 17 00:00:00 2001
From: Roman Lebedev <lebedev.ri@gmail.com>
Date: Tue, 15 Jan 2019 09:44:25 +0000
Subject: [clang][UBSan] Sanitization for alignment assumptions.

Summary:
UB isn't nice. It's cool and powerful, but not nice.
Having a way to detect it is nice though.
[[ https://wg21.link/p1007r3 | P1007R3: std::assume_aligned ]] / http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1007r2.pdf says:
```
We propose to add this functionality via a library function instead of a core language attribute.
...
If the pointer passed in is not aligned to at least N bytes, calling assume_aligned results in undefined behaviour.
```

This differential teaches clang to sanitize all the various variants of this assume-aligned attribute.

Requires D54588 for LLVM IRBuilder changes.
The compiler-rt part is D54590.

This is a second commit, the original one was r351105,
which was mass-reverted in r351159 because 2 compiler-rt tests were failing.

Reviewers: ABataev, craig.topper, vsk, rsmith, rnk, #sanitizers, erichkeane, filcab, rjmccall

Reviewed By: rjmccall

Subscribers: chandlerc, ldionne, EricWF, mclow.lists, cfe-commits, bkramer

Tags: #sanitizers

Differential Revision: https://reviews.llvm.org/D54589

llvm-svn: 351177
---
 clang/docs/ReleaseNotes.rst               | 43 +++++++++++++++++++++++++++++++
 clang/docs/UndefinedBehaviorSanitizer.rst |  2 +-
 2 files changed, 44 insertions(+), 1 deletion(-)

(limited to 'clang/docs')

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 64991343d9de..b6a405dbc78b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -321,6 +321,49 @@ Undefined Behavior Sanitizer (UBSan)
 * The Implicit Conversion Sanitizer (``-fsanitize=implicit-conversion``) has
   learned to sanitize compound assignment operators.
 
+* ``alignment`` check has learned to sanitize the assume_aligned-like attributes:
+
+  .. code-block:: c++
+
+      typedef char **__attribute__((align_value(1024))) aligned_char;
+      struct ac_struct {
+        aligned_char a;
+      };
+      char **load_from_ac_struct(struct ac_struct *x) {
+        return x->a; // <- check that loaded 'a' is aligned
+      }
+
+      char **passthrough(__attribute__((align_value(1024))) char **x) {
+        return x; // <- check the pointer passed as function argument
+      }
+
+      char **__attribute__((alloc_align(2)))
+      alloc_align(int size, unsigned long alignment);
+
+      char **caller(int size) {
+        return alloc_align(size, 1024); // <- check returned pointer
+      }
+
+      char **__attribute__((assume_aligned(1024))) get_ptr();
+
+      char **caller2() {
+        return get_ptr(); // <- check returned pointer
+      }
+
+      void *caller3(char **x) {
+        return __builtin_assume_aligned(x, 1024);  // <- check returned pointer
+      }
+
+      void *caller4(char **x, unsigned long offset) {
+        return __builtin_assume_aligned(x, 1024, offset);  // <- check returned pointer accounting for the offest
+      }
+
+      void process(char *data, int width) {
+          #pragma omp for simd aligned(data : 1024) // <- aligned clause will be checked.
+          for (int x = 0; x < width; x++)
+          data[x] *= data[x];
+      }
+
 Core Analysis Improvements
 ==========================
 
diff --git a/clang/docs/UndefinedBehaviorSanitizer.rst b/clang/docs/UndefinedBehaviorSanitizer.rst
index ddffee85c98d..3700d4962d36 100644
--- a/clang/docs/UndefinedBehaviorSanitizer.rst
+++ b/clang/docs/UndefinedBehaviorSanitizer.rst
@@ -72,7 +72,7 @@ Available checks
 Available checks are:
 
   -  ``-fsanitize=alignment``: Use of a misaligned pointer or creation
-     of a misaligned reference.
+     of a misaligned reference. Also sanitizes assume_aligned-like attributes.
   -  ``-fsanitize=bool``: Load of a ``bool`` value which is neither
      ``true`` nor ``false``.
   -  ``-fsanitize=builtin``: Passing invalid values to compiler builtins.
-- 
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