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https://gitlab.gnome.org/GNOME/glib.git
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Align the reference counted allocations
We need stronger alignment guarantees for the memory allocations done through g_rc_box_alloc_full(): while the passed block size may be aligned, we're not aligning the private data size; this means the overall allocation may become unaligned, and this could raise issues when we use the private data size as an offset to access the reference count. Fixes: #1581
This commit is contained in:
Emmanuele Bassi
parent
2a64176b83
commit
87f0a5a219
@ -177,7 +177,7 @@ g_atomic_rc_box_alloc (gsize block_size)
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{
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g_return_val_if_fail (block_size > 0, NULL);
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return g_rc_box_alloc_full (block_size, TRUE, FALSE);
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return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, TRUE, FALSE);
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}
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/**
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@ -201,7 +201,7 @@ g_atomic_rc_box_alloc0 (gsize block_size)
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{
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g_return_val_if_fail (block_size > 0, NULL);
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return g_rc_box_alloc_full (block_size, TRUE, TRUE);
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return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, TRUE, TRUE);
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}
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/**
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@ -262,7 +262,7 @@ gpointer
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g_return_val_if_fail (block_size > 0, NULL);
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g_return_val_if_fail (mem_block != NULL, NULL);
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res = g_rc_box_alloc_full (block_size, TRUE, FALSE);
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res = g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, TRUE, FALSE);
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memcpy (res, mem_block, block_size);
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return res;
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@ -339,13 +339,15 @@ g_atomic_rc_box_release_full (gpointer mem_block,
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if (g_atomic_ref_count_dec (&real_box->ref_count))
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{
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char *real_mem = (char *) real_box - real_box->private_offset;
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TRACE (GLIB_RCBOX_RELEASE (mem_block, 1));
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if (clear_func != NULL)
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clear_func (mem_block);
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TRACE (GLIB_RCBOX_FREE (mem_block));
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g_free (real_box);
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g_free (real_mem);
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}
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}
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@ -162,25 +162,49 @@
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* Since: 2.58.
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*/
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#define G_RC_BOX(p) (GRcBox *) (((char *) (p)) - G_RC_BOX_SIZE)
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/* We use the same alignment as GTypeInstance and GNU libc's malloc */
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#define STRUCT_ALIGNMENT (2 * sizeof (gsize))
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#define ALIGN_STRUCT(offset) ((offset + (STRUCT_ALIGNMENT - 1)) & -STRUCT_ALIGNMENT)
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#define G_RC_BOX(p) (GRcBox *) (((char *) (p)) - G_RC_BOX_SIZE)
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gpointer
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g_rc_box_alloc_full (gsize block_size,
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gsize alignment,
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gboolean atomic,
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gboolean clear)
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{
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/* sizeof GArcBox == sizeof GRcBox */
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/* We don't do an (atomic ? G_ARC_BOX_SIZE : G_RC_BOX_SIZE) check, here
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* because we have a static assertion that sizeof(GArcBox) == sizeof(GRcBox)
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* inside grcboxprivate.h, and we don't want the compiler to unnecessarily
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* warn about both branches of the conditional yielding identical results
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*/
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gsize private_size = G_ARC_BOX_SIZE;
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gsize private_offset = 0;
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gsize real_size;
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char *allocated;
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g_assert (block_size < (G_MAXSIZE - G_ARC_BOX_SIZE));
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g_assert (alignment != 0);
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/* We need to ensure that the private data is aligned */
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if (private_size % alignment != 0)
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{
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private_offset = private_size % alignment;
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private_size += (alignment - private_offset);
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}
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g_assert (block_size < (G_MAXSIZE - private_size));
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real_size = private_size + block_size;
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/* The real allocated size must be a multiple of @alignment, to
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* maintain the alignment of block_size
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*/
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if (real_size % alignment != 0)
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{
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gsize offset = real_size % alignment;
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g_assert (real_size < (G_MAXSIZE - (alignment - offset)));
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real_size += (alignment - offset);
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}
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#ifdef ENABLE_VALGRIND
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if (RUNNING_ON_VALGRIND)
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{
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@ -214,8 +238,18 @@ g_rc_box_alloc_full (gsize block_size,
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if (atomic)
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{
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GArcBox *real_box = (GArcBox *) allocated;
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/* We leave the alignment padding at the top of the allocation,
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* so we have an in memory layout of:
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*
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* |[ offset ][ sizeof(GArcBox) ]||[ block_size ]|
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*/
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GArcBox *real_box = (GArcBox *) (allocated + private_offset);
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/* Store the real size */
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real_box->mem_size = block_size;
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/* Store the alignment offset, to be used when freeing the
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* allocated block
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*/
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real_box->private_offset = private_offset;
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#ifndef G_DISABLE_ASSERT
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real_box->magic = G_BOX_MAGIC;
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#endif
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@ -223,8 +257,18 @@ g_rc_box_alloc_full (gsize block_size,
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}
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else
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{
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GRcBox *real_box = (GRcBox *) allocated;
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/* We leave the alignment padding at the top of the allocation,
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* so we have an in memory layout of:
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*
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* |[ offset ][ sizeof(GRcBox) ]||[ block_size ]|
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*/
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GRcBox *real_box = (GRcBox *) (allocated + private_offset);
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/* Store the real size */
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real_box->mem_size = block_size;
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/* Store the alignment offset, to be used when freeing the
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* allocated block
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*/
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real_box->private_offset = private_offset;
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#ifndef G_DISABLE_ASSERT
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real_box->magic = G_BOX_MAGIC;
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#endif
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@ -255,7 +299,7 @@ g_rc_box_alloc (gsize block_size)
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{
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g_return_val_if_fail (block_size > 0, NULL);
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return g_rc_box_alloc_full (block_size, FALSE, FALSE);
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return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, FALSE, FALSE);
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}
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/**
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@ -279,7 +323,7 @@ g_rc_box_alloc0 (gsize block_size)
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{
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g_return_val_if_fail (block_size > 0, NULL);
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return g_rc_box_alloc_full (block_size, FALSE, TRUE);
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return g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, FALSE, TRUE);
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}
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/**
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@ -339,7 +383,7 @@ gpointer
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g_return_val_if_fail (block_size > 0, NULL);
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g_return_val_if_fail (mem_block != NULL, NULL);
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res = g_rc_box_alloc_full (block_size, FALSE, FALSE);
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res = g_rc_box_alloc_full (block_size, STRUCT_ALIGNMENT, FALSE, FALSE);
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memcpy (res, mem_block, block_size);
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return res;
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@ -416,13 +460,15 @@ g_rc_box_release_full (gpointer mem_block,
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if (g_ref_count_dec (&real_box->ref_count))
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{
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char *real_mem = (char *) real_box - real_box->private_offset;
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TRACE (GLIB_RCBOX_RELEASE (mem_block, 0));
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if (clear_func != NULL)
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clear_func (mem_block);
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TRACE (GLIB_RCBOX_FREE (mem_block));
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g_free (real_box);
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g_free (real_mem);
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}
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}
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@ -27,6 +27,7 @@ typedef struct {
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grefcount ref_count;
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gsize mem_size;
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gsize private_offset;
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#ifndef G_DISABLE_ASSERT
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/* A "magic" number, used to perform additional integrity
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@ -40,6 +41,7 @@ typedef struct {
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gatomicrefcount ref_count;
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gsize mem_size;
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gsize private_offset;
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#ifndef G_DISABLE_ASSERT
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guint32 magic;
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@ -51,10 +53,18 @@ typedef struct {
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/* Keep the two refcounted boxes identical in size */
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G_STATIC_ASSERT (sizeof (GRcBox) == sizeof (GArcBox));
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/* This is the default alignment we use when allocating the
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* refcounted memory blocks; it's similar to the alignment
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* guaranteed by the malloc() in GNU's libc and by the GSlice
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* allocator
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*/
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#define STRUCT_ALIGNMENT (2 * sizeof (gsize))
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#define G_RC_BOX_SIZE sizeof (GRcBox)
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#define G_ARC_BOX_SIZE sizeof (GArcBox)
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gpointer g_rc_box_alloc_full (gsize block_size,
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gsize alignment,
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gboolean atomic,
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gboolean clear);
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