On 21.08.19 11:09, Paul Durrant wrote:
Hi, Paul
}
+void *_xrealloc(void *ptr, unsigned long size, unsigned long align)
+{
+ unsigned long curr_size, tmp_size;
+ void *p;
+
+ if ( !size )
+ {
+ xfree(ptr);
+ return ZERO_BLOCK_PTR;
+ }
+
+ if ( ptr == NULL || ptr == ZERO_BLOCK_PTR )
+ return _xmalloc(size, align);
+
+ if ( !((unsigned long)ptr & (PAGE_SIZE - 1)) )
+ curr_size = PFN_ORDER(virt_to_page(ptr)) << PAGE_SHIFT;
+ else
+ {
+ struct bhdr *b;
+ b = (struct bhdr *)((char *)ptr - BHDR_OVERHEAD);
+ curr_size = b->size & BLOCK_SIZE_MASK;
+ }
That seconds clause is not going to give you the block size if the previous
allocation had alignment padding. You'll need to check the FREE_BLOCK bit to
tell whether it's a real block header or the 'fake' alignment header and then
maybe walk backwards onto the real header. See the code in xfree().
Indeed. Thank you for the pointer.
You should also check whether the new requested alignment is compatible with
the existing block alignment
I am wondering:
In case when we use only type-safe construction for the basic allocation
(xmalloc) and type-safe construction for the re-allocation
(xrealloc_flex_struct) over the same pointer of the correct type, will
we get a possible alignment incompatibility?
This is how I see it:
diff --git a/xen/common/xmalloc_tlsf.c b/xen/common/xmalloc_tlsf.c
index eecae2e..f90f453 100644
--- a/xen/common/xmalloc_tlsf.c
+++ b/xen/common/xmalloc_tlsf.c
@@ -616,8 +616,15 @@ void *_xrealloc(void *ptr, unsigned long size,
unsigned long align)
curr_size = PFN_ORDER(virt_to_page(ptr)) << PAGE_SHIFT;
else
{
- struct bhdr *b;
- b = (struct bhdr *)((char *)ptr - BHDR_OVERHEAD);
+ struct bhdr *b = (struct bhdr *)((char *)ptr - BHDR_OVERHEAD);
+
+ if ( b->size & FREE_BLOCK )
+ {
+ p = (char *)ptr - (b->size & ~FREE_BLOCK);
+ b = (struct bhdr *)((char *)p - BHDR_OVERHEAD);
+ ASSERT(!(b->size & FREE_BLOCK));
+ }
+
curr_size = b->size & BLOCK_SIZE_MASK;
}
@@ -630,8 +637,8 @@ void *_xrealloc(void *ptr, unsigned long size,
unsigned long align)
tmp_size = ( tmp_size < MIN_BLOCK_SIZE ) ? MIN_BLOCK_SIZE :
ROUNDUP_SIZE(tmp_size);
- if ( tmp_size <= curr_size ) /* fits in current block */
- return ptr;
+ if ( tmp_size <= curr_size && ((unsigned long)ptr & (align - 1)) == 0 )
+ return ptr; /* fits in current block */
p = _xmalloc(size, align);
if ( p )
(END)
Did I get your point correct?
--
Regards,
Oleksandr Tyshchenko
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