[docs][msan] List common cases reported by msan

[vitalybuka]

Fixes google/sanitizers#1755.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Vitaly Buka (vitalybuka)

Changes

Fixes google/sanitizers#1755.

---

Full diff: https://github.com/llvm/llvm-project/pull/101105.diff

1 Files Affected:

• (modified) clang/docs/MemorySanitizer.rst (+8-1)

diff --git a/clang/docs/MemorySanitizer.rst b/clang/docs/MemorySanitizer.rst
index bcc6cc808e8ba..024bed25243b9 100644
--- a/clang/docs/MemorySanitizer.rst
+++ b/clang/docs/MemorySanitizer.rst
@@ -8,11 +8,18 @@ MemorySanitizer
 Introduction
 ============
 
-MemorySanitizer is a detector of uninitialized reads. It consists of a
+MemorySanitizer is a detector of uninitialized memory use. It consists of a
 compiler instrumentation module and a run-time library.
 
 Typical slowdown introduced by MemorySanitizer is **3x**.
 
+Here is a not comprehensive list cases when MemorySanitizer will report an error:
+
+* Conditional branches controlled by uninitialized values.
+* Using uninitalized pointers for memory accesses.
+* Passing and returning uninitialized values to/from function calls. Can be disabled with ``-fno-sanitize-memory-param-retval``.
+* Passing uninitialized data into libc calls.
+
 How to build
 ============
 

[johnstiles-google]

Is this redundant with "Uninitialized value passed or returned from a function call"?

[vitalybuka]

In some cases they are redundant, but usually not
e.g fopen(file_path, ...)

param-retval will only check argument (pointer to C-string) if initialized
'libc` one will also check bytes in the string.

We can't check complex data structures or arrays without knowing details of called functions, but we know that about libc (glibc in case of msan)