[glibc/arm/morello/main] cheri: malloc: Use memcpy for obstack internal copy

[glibc/arm/morello/main] cheri: malloc: Use memcpy for obstack internal copy

[Szabolcs Nagy]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=807b692012ae921ac388cb2ea852645ee2ce4027

commit 807b692012ae921ac388cb2ea852645ee2ce4027
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Thu Jan 5 18:12:36 2023 +0000

    cheri: malloc: Use memcpy for obstack internal copy
    
    Internally obstack used a backward word at a time copy.  This can be
    an aliasing violation and likely slower than memcpy on most targets.
    The code is a badly written memcpy with performance issues such as
    the h->object_base indirection cannot be hoisted out of the loop.
    
    On CHERI architecture this is needed for copying pointers correctly.

Diff:
---
 malloc/obstack.c | 31 +++----------------------------
 1 file changed, 3 insertions(+), 28 deletions(-)

diff --git a/malloc/obstack.c b/malloc/obstack.c
index aad6a34f58..2056a5fe9f 100644
--- a/malloc/obstack.c
+++ b/malloc/obstack.c
@@ -57,6 +57,7 @@
 
 
 # include <stdint.h>
+# include <string.h>
 
 /* Determine default alignment.  */
 union fooround
@@ -79,15 +80,6 @@ enum
   DEFAULT_ROUNDING = sizeof (union fooround)
 };
 
-/* When we copy a long block of data, this is the unit to do it with.
-   On some machines, copying successive ints does not work;
-   in such a case, redefine COPYING_UNIT to 'long' (if that works)
-   or 'char' as a last resort.  */
-# ifndef COPYING_UNIT
-#  define COPYING_UNIT int
-# endif
-
-
 /* The functions allocating more room by calling 'obstack_chunk_alloc'
    jump to the handler pointed to by 'obstack_alloc_failed_handler'.
    This can be set to a user defined function which should either
@@ -273,25 +265,8 @@ _obstack_newchunk (struct obstack *h, int length)
   object_base =
     __PTR_ALIGN ((char *) new_chunk, new_chunk->contents, h->alignment_mask);
 
-  /* Move the existing object to the new chunk.
-     Word at a time is fast and is safe if the object
-     is sufficiently aligned.  */
-  if (h->alignment_mask + 1 >= DEFAULT_ALIGNMENT)
-    {
-      for (i = obj_size / sizeof (COPYING_UNIT) - 1;
-	   i >= 0; i--)
-	((COPYING_UNIT *) object_base)[i]
-	  = ((COPYING_UNIT *) h->object_base)[i];
-      /* We used to copy the odd few remaining bytes as one extra COPYING_UNIT,
-	 but that can cross a page boundary on a machine
-	 which does not do strict alignment for COPYING_UNITS.  */
-      already = obj_size / sizeof (COPYING_UNIT) * sizeof (COPYING_UNIT);
-    }
-  else
-    already = 0;
-  /* Copy remaining bytes one by one.  */
-  for (i = already; i < obj_size; i++)
-    object_base[i] = h->object_base[i];
+  /* Move the existing object to the new chunk.  */
+  memcpy (object_base, h->object_base, obj_size);
 
   /* If the object just copied was the only data in OLD_CHUNK,
      free that chunk and remove it from the chain.