[ruby-core:102697] [Ruby master Bug#17540] A segfault due to Clang/LLVM optimization on 32-bit ARM Linux

Issue #17540 has been updated by shyouhei (Shyouhei Urabe).


This is my take:

```patch
From 7fb39b1138dfaa3a1502673ac82d6b75401e8f39 Mon Sep 17 00:00:00 2001
From: 卜部昌平 <[e-mail]>
Date: Tue, 2 Mar 2021 15:22:22 +0900
Subject: [PATCH] fix strict aliasing

---
 internal/object.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/internal/object.h b/internal/object.h
index aa820128c7..6a5dfcda63 100644
--- a/internal/object.h
+++ b/internal/object.h
@@ -47,8 +47,8 @@ MJIT_SYMBOL_EXPORT_END
 static inline void
 RBASIC_SET_CLASS_RAW(VALUE obj, VALUE klass)
 {
-    struct { VALUE flags; VALUE klass; } *ptr = (void *)obj;
-    ptr->klass = klass;
+    VALUE *ptr =(/* const cast */VALUE *) & RBASIC(obj)->klass;
+    memcpy(ptr, &klass, sizeof(klass));
 }
 
 static inline void
-- 
2.17.1

```

I would like to reflain from fixing this issue by adding compiler-specific `__asm__` or `__attreibute__`, because that does not help everyone...  The world is not built on top of LLVM.  I don't want to kill support for other compiler infrastructures.

It sounds like a nice idea to have `-fno-strict-aliasing`, though.  That is just a matter of compiler flag.  Must not hurt the codebase.

----------------------------------------
Bug #17540: A segfault due to Clang/LLVM optimization on 32-bit ARM Linux 
https://bugs.ruby-lang.org/issues/17540#change-90692

* Author: xtkoba (Tee KOBAYASHI)
* Status: Open
* Priority: Normal
* ruby -v: ruby 3.0.0p0 (2020-12-25 revision 95aff21468) [armv7a-linux-eabi]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN
----------------------------------------
When built with `optflags=-O3` (which is the default), `ruby -e "pp Thread.main"` causes a segfault, which seems to be worked around by the following change:
```
--- a/include/ruby/internal/fl_type.h
+++ b/include/ruby/internal/fl_type.h
@@ -231,7 +231,7 @@
 RBIMPL_ATTR_PURE_UNLESS_DEBUG()
 RBIMPL_ATTR_ARTIFICIAL()
 static inline VALUE
-RB_FL_TEST_RAW(VALUE obj, VALUE flags)
+RB_FL_TEST_RAW(volatile VALUE obj, VALUE flags)
 {
     RBIMPL_ASSERT_OR_ASSUME(RB_FL_ABLE(obj));
     return RBASIC(obj)->flags & flags;
```

There might be a bug in the optimizer of Clang/LLVM (version 11.0.1).



-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:[e-mail]?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>