[asan] Enable detect_stack_use_after_return=1 by default on Linux

[vitalybuka]

Summary

By default -fsanitize=address already compiles with this check, why not use it.
For compatibly it can be disabled with env ASAN_OPTIONS=detect_stack_use_after_return=0.

[hans]

Sounds good to me.

Worth a release note maybe?

[vitalybuka]

add release note

[vitalybuka]

clang/docs/ReleaseNotes.rst

180–183

@hans PTAL

180–183

I'll move MSAN_OPTIONS into a separate patch if this format is OK

[hans]

clang/docs/ReleaseNotes.rst

180–183

lgtm

[vitalybuka]

redo

clang/docs/AddressSanitizer.rst

 
 AddressSanitizer is a fast memory error detector. It consists of a compiler
 instrumentation module and a run-time library. The tool can detect the
 following types of bugs:
 
 * Out-of-bounds accesses to heap, stack and globals
 * Use-after-free
 * Use-after-return (clang flag ``-fsanitize-address-use-after-return=(never|runtime|always)`` default: ``runtime``)
-    * Enable ``runtime`` with: ``ASAN_OPTIONS=detect_stack_use_after_return=1``
+    * Enable with: ``ASAN_OPTIONS=detect_stack_use_after_return=1`` (already enabled on Linux).
+    * Disable with: ``ASAN_OPTIONS=detect_stack_use_after_return=0``.
 * Use-after-scope (clang flag ``-fsanitize-address-use-after-scope``)
 * Double-free, invalid free
 * Memory leaks (experimental)
 
 Typical slowdown introduced by AddressSanitizer is **2x**.
 
 How to build
 ============

clang/docs/ReleaseNotes.rst

- ``-Wmisexpect`` warns when the branch weights collected during profiling
   conflict with those added by ``llvm.expect``.
 
 Non-comprehensive list of changes in this release
 -------------------------------------------------
 - Improve __builtin_dump_struct:
   - Support bitfields in struct and union.
   - Improve the dump format, dump both bitwidth(if its a bitfield) and field value.
   - Remove anonymous tag locations.
   - Beautify dump format, add indent for nested struct and struct members.
-- Enable MSAN_OPTIONS=poison_in_dtor=1 by default.
+- Previously disabled sanitizer options now enabled by default:
+  - ASAN_OPTIONS=detect_stack_use_after_return=1 (only on Linux).
+  - MSAN_OPTIONS=poison_in_dtor=1.
 
 New Compiler Flags
 ------------------
 - Added the ``-fno-knr-functions`` flag to allow users to opt into the C2x
   behavior where a function with an empty parameter list is treated as though
   the parameter list were ``void``. There is no ``-fknr-functions`` or
   ``-fno-no-knr-functions`` flag; this feature cannot be disabled in language
   modes where it is required, such as C++ or C2x.

compiler-rt/lib/asan/asan_flags.inc

 ASAN_FLAG(bool, check_initialization_order, false,
           "If set, attempts to catch initialization order issues.")
 ASAN_FLAG(
     bool, replace_str, true,
     "If set, uses custom wrappers and replacements for libc string functions "
     "to find more errors.")
 ASAN_FLAG(bool, replace_intrin, true,
           "If set, uses custom wrappers for memset/memcpy/memmove intrinsics.")
-ASAN_FLAG(bool, detect_stack_use_after_return, false,
+ASAN_FLAG(bool, detect_stack_use_after_return,
+          SANITIZER_LINUX && !SANITIZER_ANDROID,
           "Enables stack-use-after-return checking at run-time.")
-ASAN_FLAG(int, min_uar_stack_size_log, 16, // We can't do smaller anyway.
+ASAN_FLAG(int, min_uar_stack_size_log, 16,  // We can't do smaller anyway.
           "Minimum fake stack size log.")
 ASAN_FLAG(int, max_uar_stack_size_log,
           20, // 1Mb per size class, i.e. ~11Mb per thread
           "Maximum fake stack size log.")
 ASAN_FLAG(bool, uar_noreserve, false,
           "Use mmap with 'noreserve' flag to allocate fake stack.")
 ASAN_FLAG(
     int, max_malloc_fill_size, 0x1000,  // By default, fill only the first 4K.