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gvariant-core: Don’t call posix_memalign() with size==0

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While glibc is fine with it (and returns a `NULL` pointer), technically
it’s implementation-defined behaviour according to POSIX, so it’s best
avoided.

See
https://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_memalign.html.

In particular, valgrind will warn about it, which is causing failures of
the gdbus-codegen tests when valgrind is enabled. For example,
https://gitlab.gnome.org/GNOME/glib/-/jobs/3460673 gives
```
==15276== posix_memalign() invalid size value: 0
==15276==    at 0x484B7BC: posix_memalign (vg_replace_malloc.c:2099)
==15276==    by 0x49320B2: g_variant_new_from_bytes (gvariant-core.c:629)
==15276==    by 0x4931853: g_variant_new_from_data (gvariant.c:6226)
==15276==    by 0x4B9A951: g_dbus_gvalue_to_gvariant (gdbusutils.c:708)
==15276==    by 0x41BD15: _foo_igen_bat_skeleton_handle_get_property (gdbus-test-codegen-generated.c:13503)
==15276==    by 0x41BFAF: foo_igen_bat_skeleton_dbus_interface_get_properties (gdbus-test-codegen-generated.c:13582)
…
```

Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Helps: #3228
This commit is contained in:
Philip Withnall 2024-01-16 09:59:13 +00:00
parent 554eb407de
commit 635f8d43eb
2 changed files with 20 additions and 5 deletions
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10
glib/gvariant-core.c
View File

@ -625,8 +625,14 @@ g_variant_new_from_bytes (const GVariantType *type,
/* posix_memalign() requires the alignment to be a multiple of /* posix_memalign() requires the alignment to be a multiple of
* sizeof(void*), and a power of 2. See g_variant_type_info_query() for * sizeof(void*), and a power of 2. See g_variant_type_info_query() for
* details on the alignment format. */ * details on the alignment format.
if (posix_memalign (&aligned_data, MAX (sizeof (void *), alignment + 1), *
* While calling posix_memalign() with aligned_size==0 is safe on glibc,
* POSIX specifies that the behaviour is implementation-defined, so avoid
* that and leave aligned_data==NULL in that case.
* See https://pubs.opengroup.org/onlinepubs/9699919799/functions/posix_memalign.html */
if (aligned_size != 0 &&
posix_memalign (&aligned_data, MAX (sizeof (void *), alignment + 1),
aligned_size) != 0) aligned_size) != 0)
g_error ("posix_memalign failed"); g_error ("posix_memalign failed");

15
glib/tests/gvariant.c
View File

@ -1337,12 +1337,15 @@ flavoured_free (gpointer data,
static gpointer static gpointer
align_malloc (gsize size) align_malloc (gsize size)
{ {
gpointer mem; gpointer mem = NULL;
#ifdef HAVE_POSIX_MEMALIGN #ifdef HAVE_POSIX_MEMALIGN
/* posix_memalign() requires the alignment to be a multiple of /* posix_memalign() requires the alignment to be a multiple of
* sizeof(void*), and a power of 2. */ * sizeof(void*), and a power of 2.
if (posix_memalign (&mem, MAX (sizeof (void *), 8), size)) * Calling it with size==0 leads to implementation-defined behaviour, so avoid
* that and guarantee to return NULL. */
if (size != 0 &&
posix_memalign (&mem, MAX (sizeof (void *), 8), size))
g_error ("posix_memalign failed"); g_error ("posix_memalign failed");
#else #else
/* NOTE: there may be platforms that lack posix_memalign() and also /* NOTE: there may be platforms that lack posix_memalign() and also
@ -4959,6 +4962,12 @@ test_gbytes (void)
g_bytes_unref (bytes2); g_bytes_unref (bytes2);
g_variant_unref (a); g_variant_unref (a);
g_variant_unref (tuple); g_variant_unref (tuple);
bytes = g_bytes_new (NULL, 0);
a = g_variant_new_from_bytes (G_VARIANT_TYPE ("as"), bytes, TRUE);
g_bytes_unref (bytes);
g_assert_cmpuint (g_variant_n_children (a), ==, 0);
g_variant_unref (a);
} }
typedef struct { typedef struct {