From 2b192b406ce0121c7e771b8f52cd0b6361bde2d6 Mon Sep 17 00:00:00 2001 From: Simon McVittie Date: Mon, 15 Feb 2016 15:00:22 +0000 Subject: [PATCH 3/4] DBusMessageIter: eliminate padding on 64-bit platforms Previously, 64-bit (LP64 or LLP64) platforms would have had 32 bits of padding between pad2 and pad3. We want to guarantee that an ISO C compiler will copy the entire struct when assigning between structs, but padding is not guaranteed to be copied, so we want to ensure that the struct is "packed". Statically assert that the old ABI is compatible with the new ABI. Signed-off-by: Simon McVittie Bug: https://bugs.freedesktop.org/show_bug.cgi?id=94136 --- dbus/dbus-message.c | 29 +++++++++++++++++++++++++++++ dbus/dbus-message.h | 2 +- 2 files changed, 30 insertions(+), 1 deletion(-) diff --git a/dbus/dbus-message.c b/dbus/dbus-message.c index 50e87ca..4c34e96 100644 --- a/dbus/dbus-message.c +++ b/dbus/dbus-message.c @@ -136,6 +136,29 @@ struct DBusMessageRealIter } u; /**< the type writer or reader that does all the work */ }; +/** + * Layout of a DBusMessageIter on the stack in dbus 1.10.0. This is no + * longer used, but for ABI compatibility we need to assert that the + * new layout is the same size. + */ +typedef struct +{ + void *dummy1; + void *dummy2; + dbus_uint32_t dummy3; + int dummy4; + int dummy5; + int dummy6; + int dummy7; + int dummy8; + int dummy9; + int dummy10; + int dummy11; + int pad1; + int pad2; + void *pad3; +} DBusMessageIter_1_10_0; + static void get_const_signature (DBusHeader *header, const DBusString **type_str_p, @@ -2029,6 +2052,12 @@ _dbus_message_iter_init_common (DBusMessage *message, _DBUS_STATIC_ASSERT (sizeof (DBusMessageRealIter) <= sizeof (DBusMessageIter)); _DBUS_STATIC_ASSERT (_DBUS_ALIGNOF (DBusMessageRealIter) <= _DBUS_ALIGNOF (DBusMessageIter)); + /* A failure of these two assertions would indicate that we've broken + * ABI on this platform since 1.10.0. */ + _DBUS_STATIC_ASSERT (sizeof (DBusMessageIter_1_10_0) >= + sizeof (DBusMessageIter)); + _DBUS_STATIC_ASSERT (_DBUS_ALIGNOF (DBusMessageIter_1_10_0) >= + _DBUS_ALIGNOF (DBusMessageIter)); /* Since the iterator will read or write who-knows-what from the * message, we need to get in the right byte order diff --git a/dbus/dbus-message.h b/dbus/dbus-message.h index 3e33eb7..ac3e408 100644 --- a/dbus/dbus-message.h +++ b/dbus/dbus-message.h @@ -62,7 +62,7 @@ struct DBusMessageIter int dummy10; /**< Don't use this */ int dummy11; /**< Don't use this */ int pad1; /**< Don't use this */ - int pad2; /**< Don't use this */ + void *pad2; /**< Don't use this */ void *pad3; /**< Don't use this */ }; -- 2.7.0