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gatomicarray: suppress valgrind memory leak warnings

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The problem occurs because we keep a pointer inside the allocated block,
instead of a pointer to the start of the block:

```
==180238== 16 bytes in 1 blocks are possibly lost in loss record 3,086 of 16,075
==180238==    at 0x483980B: malloc (vg_replace_malloc.c:309)
==180238==    by 0x548942C: g_malloc (gmem.c:102)
==180238==    by 0x54A4748: g_slice_alloc (gslice.c:1025)
==180238==    by 0x53D0AAF: freelist_alloc (gatomicarray.c:77)
==180238==    by 0x53D0B85: _g_atomic_array_copy (gatomicarray.c:133)
==180238==    by 0x53F8E6D: iface_node_set_offset_L (gtype.c:1347)
==180238==    by 0x53F91F1: type_node_add_iface_entry_W (gtype.c:1444)
==180238==    by 0x53F93DF: type_add_interface_Wm (gtype.c:1477)
==180238==    by 0x53FC946: g_type_add_interface_static (gtype.c:2852)
==180238==    by 0x4A3D53A: gtk_menu_shell_accessible_get_type_once (gtkmenushellaccessible.c:26)
==180238==    by 0x4A3D495: gtk_menu_shell_accessible_get_type (gtkmenushellaccessible.c:26)
==180238==    by 0x4C8AC44: gtk_menu_shell_class_init (gtkmenushell.c:424)
```

Note we cannot use VALGRIND_FREELIKE_BLOCK() in freelist_free() because we
have not actually freed the FreeListNode and need to dereference it in
freelist_alloc() to decide whether to reuse the block. That would result
in a use-after-free warning before we would get a chance to call
VALGRIND_MALLOCLIKE_BLOCK() in the reuse path.

Also note that this free list only ever grows: it never shrinks for the
lifetime of the application, so nothing here will ever be truely freed,
although unused elements are eligible for reuse.

Fix suggested by Philip Withnall

Related: #2076
This commit is contained in:
Michael Catanzaro 2020-11-23 15:51:16 -06:00
parent 23ad18791d
commit a412ffe4d3
1 changed files with 6 additions and 0 deletions
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6
gobject/gatomicarray.c
View File

@ -17,6 +17,7 @@
#include "config.h"
#include "../glib/gvalgrind.h"
#include <string.h>
#include "gatomicarray.h"
@ -77,6 +78,11 @@ freelist_alloc (gsize size, gboolean reuse)
mem = g_slice_alloc (real_size);
mem = ((char *) mem) + sizeof (gsize);
G_ATOMIC_ARRAY_DATA_SIZE (mem) = size;
#if ENABLE_VALGRIND
VALGRIND_MALLOCLIKE_BLOCK (mem, real_size - sizeof (gsize), FALSE, FALSE);
#endif
return mem;
}