[ruby-core:109149] [Ruby master Bug#18893] Don't redefine memcpy(3)

Issue #18893 has been updated by shyouhei (Shyouhei Urabe).


This is my take:

```patch
From 505d00311d82fdbed80688e9db792c3b54b8ee27 Mon Sep 17 00:00:00 2001
From: 卜部昌平 <[e-mail]>
Date: Wed, 6 Jul 2022 09:18:28 +0900
Subject: [PATCH] do not define our own version of memcpy

The (sole) use of memcpy in our public header is now replaced to
directly call ruby_nonempty_memcpy, and the previous definition of
memcpy is now internal-only.
---
 include/ruby/internal/memory.h | 6 +-----
 internal.h                     | 3 +++
 2 files changed, 4 insertions(+), 5 deletions(-)

diff --git a/include/ruby/internal/memory.h b/include/ruby/internal/memory.h
index aa3464465d..0f59262a91 100644
--- a/include/ruby/internal/memory.h
+++ b/include/ruby/internal/memory.h
@@ -363,7 +363,7 @@ typedef uint128_t DSIZE_T;
  * @return  `p1`.
  * @post    First `n` elements of `p2` are copied into `p1`.
  */
-#define MEMCPY(p1,p2,type,n) memcpy((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
+#define MEMCPY(p1,p2,type,n) ruby_nonempty_memcpy((p1), (p2), rbimpl_size_mul_or_raise(sizeof(type), (n)))
 
 /**
  * Handy macro to call memmove.
@@ -644,7 +644,6 @@ rb_alloc_tmp_buffer2(volatile VALUE *store, long count, size_t elsize)
     return rb_alloc_tmp_buffer_with_count(store, total_size, cnt);
 }
 
-#if ! defined(__MINGW32__) && ! defined(__DOXYGEN__)
 RBIMPL_SYMBOL_EXPORT_BEGIN()
 RBIMPL_ATTR_NOALIAS()
 RBIMPL_ATTR_NONNULL((1))
@@ -663,8 +662,5 @@ ruby_nonempty_memcpy(void *dest, const void *src, size_t n)
     }
 }
 RBIMPL_SYMBOL_EXPORT_END()
-#undef memcpy
-#define memcpy ruby_nonempty_memcpy
-#endif
 
 #endif /* RBIMPL_MEMORY_H */
diff --git a/internal.h b/internal.h
index 00a8295295..7e1abcbab8 100644
--- a/internal.h
+++ b/internal.h
@@ -106,4 +106,7 @@ RUBY_SYMBOL_EXPORT_END
 #define RBOOL(v) ((v) ? Qtrue : Qfalse)
 #define RB_BIGNUM_TYPE_P(x) RB_TYPE_P((x), T_BIGNUM)
 
+#ifndef __MINGW32
+#define memcpy ruby_nonempty_memcpy
+#endif
 #endif /* RUBY_INTERNAL_H */
-- 
2.17.1

```

----------------------------------------
Bug #18893: Don't redefine memcpy(3)
https://bugs.ruby-lang.org/issues/18893#change-98289

* Author: alx (Alejandro Colomar)
* Status: Open
* Priority: Normal
* Assignee: shyouhei (Shyouhei Urabe)
* ruby -v: ruby 3.0.4p208 (2022-04-12 revision 3fa771dded) [x86_64-linux-gnu]
* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN
----------------------------------------
It is Undefined Behavior, by any standard ever issued.


See what I have in my system right now:


```
alx@asus5775:/usr/include$ grepc memcpy
./string.h:43:
extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
		     size_t __n) __THROW __nonnull ((1, 2));


./x86_64-linux-gnu/ruby-3.0.0/rb_mjit_min_header-3.0.4.h:1520:
extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
       size_t __n) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__nonnull__ (1, 2)));


./x86_64-linux-gnu/ruby-3.0.0/rb_mjit_min_header-3.0.4.h:1670:
extern __inline __attribute__ ((__always_inline__)) __attribute__ ((__gnu_inline__)) __attribute__ ((__artificial__)) void *
__attribute__ ((__nothrow__ , __leaf__)) memcpy (void *__restrict __dest, const void *__restrict __src, size_t __len)
{
  return __builtin___memcpy_chk (__dest, __src, __len,
     __builtin_object_size (__dest, 0));
}


./ruby-3.0.0/ruby/internal/memory.h:278:
#define memcpy ruby_nonempty_memcpy


./x86_64-linux-gnu/ruby-3.0.0/rb_mjit_min_header-3.0.4.h:22679:
#define memcpy ruby_nonempty_memcpy


$ grepc ruby_nonempty_memcpy
./ruby-3.0.0/ruby/internal/memory.h:266:
static inline void *
ruby_nonempty_memcpy(void *dest, const void *src, size_t n)
{
    if (n) {
        return memcpy(dest, src, n);
    }
    else {
        return dest;
    }
}


./x86_64-linux-gnu/ruby-3.0.0/rb_mjit_min_header-3.0.4.h:5673:
__attribute__((__nonnull__ (1)))
__attribute__((__returns_nonnull__))
static inline void *
ruby_nonempty_memcpy(void *dest, const void *src, size_t n)
{
    if (n) {
        return memcpy(dest, src, n);
    }
    else {
        return dest;
    }
}
```

Some code that I maintain includes some ruby headers, which end up defining memcpy(3) to that thing.  Then, my code calls memcpy(3) from a function, which happens to be inline (yes, inline, not static inline, which is a horrible thing), and I get an error from the compiler, for using a static function within a non-static inline function.

So, I'd like you to please remove that definition from public headers, and refrain from redefining any ISO C functions.
If not, please define it to something not broken (and yes, static inline is broken, as it produces duplicated code when not inlined; you could use [[gnu::always_inline]] if you want to keep static, but don't).  Just C99 inline would be reasonable.  See also: <https://www.greenend.org.uk/rjk/tech/inline.html>

Thanks,

Alex



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