Avoid undefined behavior due to strict aliasing

This does not make XCB conform to the C99+ strict aliasing rules, but it does use attributes to prevent GCC and Clang from assuming the rules are followed in the cases where XCB does violate them. Signed-off-by: Demi Marie Obenour <demiobenour@gmail.com>
2022-10-26 21:00:57 -04:00 · 2022-10-26 21:00:57 -04:00 · 48dbb5b6ca
parent 8adb5068af
commit 48dbb5b6ca
33 changed files with 64 additions and 39 deletions
--- a/configure.ac
+++ b/configure.ac
@ -15,7 +15,7 @@ AM_INIT_AUTOMAKE([foreign dist-xz])
 AM_PATH_PYTHON([3.0])

 # Set common system defines for POSIX extensions, such as _GNU_SOURCE
-# Must be called before any macros that run the compiler (like AC_PROG_LIBTOOL)
+# Must be called before any macros that run the compiler (like LT_INIT)
 # to avoid autoconf errors.
 AC_USE_SYSTEM_EXTENSIONS
 AC_SYS_LARGEFILE
@ -27,6 +27,8 @@ LT_INIT([win32-dll])
 # Require xorg-macros minimum of 1.18 - Initial version
 m4_ifndef([XORG_MACROS_VERSION],
          [m4_fatal([must install xorg-macros 1.18 or later before running autoconf/autogen])])
+XORG_TESTSET_CFLAG([XCB_CFLAGS], [-fno-strict-aliasing])
+AC_SUBST([XCB_CFLAGS])
 XORG_MACROS_VERSION(1.18)
 XORG_DEFAULT_OPTIONS
 XORG_ENABLE_DEVEL_DOCS
@ -248,6 +250,23 @@ XCB_EXTENSION(XTest, yes)
 XCB_EXTENSION(Xv, yes)
 XCB_EXTENSION(XvMC, yes)

+AC_MSG_CHECKING([[if __attribute__((may_alias)) is supported]])
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+typedef struct x { int a; } __attribute__((may_alias)) x;
+]])],[
+AC_DEFINE([[XCB_MAY_ALIAS]], [[__attribute__((may_alias))]], [Define if __attribute__((may_alias)) works])
+AC_MSG_RESULT([[yes]])
+],[
+AC_MSG_RESULT([[no]])
+AC_MSG_CHECKING([[if -fno-strict-aliasing works]])[
+case $XCB_CFLAGS in
+*-fno-strict-aliasing*)]
+  AC_MSG_RESULT([[yes]])
+  AC_MSG_WARN([[may_alias not supported, programs must use -fno-strict-aliasing]]);;
+*)
+  AC_MSG_RESULT([[no (flags are $XCB_CFLAGS)]])
+  AC_MSG_FAILURE([[No method of suppressing strict-aliasing found]]);;
+[esac]])
 AC_ARG_WITH(serverside-support, AS_HELP_STRING([--with-serverside-support], [Build with support for server-side usage of xcb. This is still EXPERIMENTAL! ABI/API may change! (default: no)]), [XCB_SERVERSIDE_SUPPORT=$withval], [XCB_SERVERSIDE_SUPPORT=no])

 AM_CONDITIONAL(XCB_SERVERSIDE_SUPPORT, test "x$XCB_SERVERSIDE_SUPPORT" = "xyes")
--- a/src/Makefile.am
+++ b/src/Makefile.am
@ -4,7 +4,7 @@ EXTSOURCES =	xproto.c \
 		bigreq.c \
 		xc_misc.c

-AM_CFLAGS = $(BASE_CFLAGS) $(NEEDED_CFLAGS) $(XDMCP_CFLAGS)
+AM_CFLAGS = $(BASE_CFLAGS) $(NEEDED_CFLAGS) $(XDMCP_CFLAGS) $(XCB_CFLAGS)
 libxcb_la_LIBADD = $(NEEDED_LIBS) $(XDMCP_LIBS)
 libxcb_la_SOURCES = \
 		xcb_conn.c xcb_out.c xcb_in.c xcb_ext.c xcb_xid.c \
@ -249,7 +249,7 @@ nodist_libxcb_ge_la_SOURCES = ge.c ge.h
 endif

 EXTHEADERS=$(EXTSOURCES:.c=.h)
-xcbinclude_HEADERS = xcb.h xcbext.h
+xcbinclude_HEADERS = xcb.h xcbext.h config.h
 if XCB_HAVE_WIN32
 xcbinclude_HEADERS += xcb_windefs.h
 endif
--- a/src/c_client.py
+++ b/src/c_client.py
@ -279,7 +279,7 @@ def c_open(self):
    _h('#include "xcb.h"')

    _c('#ifdef HAVE_CONFIG_H')
-    _c('#include "config.h"')
+    _hc('#include "config.h"')
    _c('#endif')
    _c('#include <stdlib.h>')
    _c('#include <stdalign.h>')
@ -1642,7 +1642,7 @@ def _c_iterator(self, name):
            param[0],
            ' ' * (len(self.c_type) + 1 - len(param[0])),
            param[2])
-    _h('} %s;', self.c_iterator_type)
+    _h('} XCB_MAY_ALIAS %s;', self.c_iterator_type)

    _h_setlevel(1)
    _c_setlevel(1)
@ -2254,7 +2254,7 @@ def _c_complex(self, force_packed = False):
            if b.type.has_name:
                _h('    } %s;', b.c_field_name)

-    _h('} %s%s;', 'XCB_PACKED ' if force_packed else '', self.c_type)
+    _h('} %sXCB_MAY_ALIAS %s;', 'XCB_PACKED ' if force_packed else '', self.c_type)

 def c_struct(self, name):
    '''
@ -2756,7 +2756,7 @@ def _c_cookie(self, name):
    _h(' **/')
    _h('typedef struct %s {', self.c_cookie_type)
    _h('    unsigned int sequence;')
-    _h('} %s;', self.c_cookie_type)
+    _h('} XCB_MAY_ALIAS %s;', self.c_cookie_type)

 def _man_request(self, name, void, aux):
    param_fields = [f for f in self.fields if f.visible]
@ -2812,7 +2812,7 @@ def _man_request(self, name, void, aux):
        f.write('.SS Reply datastructure\n')
        f.write('.nf\n')
        f.write('.sp\n')
-        f.write('typedef %s %s {\n' % (self.reply.c_container, self.reply.c_type))
+        f.write('typedef XCB_MAY_ALIAS %s %s {\n' % (self.reply.c_container, self.reply.c_type))
        struct_fields = []
        maxtypelen = 0

@ -3389,7 +3389,7 @@ def c_event(self, name):
    else:
        # Typedef
        _h('')
-        _h('typedef %s %s;', _t(self.name + ('event',)), _t(name + ('event',)))
+        _h('typedef XCB_MAY_ALIAS %s %s;', _t(self.name + ('event',)), _t(name + ('event',)))

        # Create sizeof-function for eventcopies for compatibility reasons
        if self.c_need_sizeof:
@ -3424,7 +3424,7 @@ def c_error(self, name):
    else:
        # Typedef
        _h('')
-        _h('typedef %s %s;', _t(self.name + ('error',)), _t(name + ('error',)))
+        _h('typedef XCB_MAY_ALIAS %s %s;', _t(self.name + ('error',)), _t(name + ('error',)))


 # Main routine starts here
--- a/src/xcb.h
+++ b/src/xcb.h
@ -53,8 +53,14 @@ extern "C" {

 #ifdef __GNUC__
 #define XCB_PACKED __attribute__((__packed__))
+#ifndef XCB_MAY_ALIAS
+#define XCB_MAY_ALIAS __attribute__((may_alias))
+#endif
 #else
 #define XCB_PACKED
+#ifndef XCB_MAY_ALIAS
+#define XCB_MAY_ALIAS
+#endif
 #endif

 /**
--- a/xcb-composite.pc.in
+++ b/xcb-composite.pc.in
@ -8,4 +8,4 @@ Description: XCB Composite Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-xfixes
 Libs: -L${libdir} -lxcb-composite
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-damage.pc.in
+++ b/xcb-damage.pc.in
@ -8,4 +8,4 @@ Description: XCB Damage Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-xfixes
 Libs: -L${libdir} -lxcb-damage
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-dbe.pc.in
+++ b/xcb-dbe.pc.in
@ -8,4 +8,4 @@ Description: XCB Double Buffer Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-dbe
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-dpms.pc.in
+++ b/xcb-dpms.pc.in
@ -8,4 +8,4 @@ Description: XCB DPMS Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-dpms
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-dri2.pc.in
+++ b/xcb-dri2.pc.in
@ -8,4 +8,4 @@ Description: XCB DRI2 Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-dri2
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-dri3.pc.in
+++ b/xcb-dri3.pc.in
@ -8,4 +8,4 @@ Description: XCB DRI3 Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-dri3
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-ge.pc.in
+++ b/xcb-ge.pc.in
@ -8,4 +8,4 @@ Description: XCB GenericEvent Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-ge
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-glx.pc.in
+++ b/xcb-glx.pc.in
@ -8,4 +8,4 @@ Description: XCB GLX Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-glx
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-present.pc.in
+++ b/xcb-present.pc.in
@ -8,4 +8,4 @@ Description: XCB Present Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-randr xcb-xfixes xcb-sync xcb-dri3
 Libs: -L${libdir} -lxcb-present
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-randr.pc.in
+++ b/xcb-randr.pc.in
@ -8,4 +8,4 @@ Description: XCB RandR Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-render
 Libs: -L${libdir} -lxcb-randr
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-record.pc.in
+++ b/xcb-record.pc.in
@ -8,4 +8,4 @@ Description: XCB Record Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-record
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-render.pc.in
+++ b/xcb-render.pc.in
@ -8,4 +8,4 @@ Description: XCB Render Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-render
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-res.pc.in
+++ b/xcb-res.pc.in
@ -8,4 +8,4 @@ Description: XCB X-Resource Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-res
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-screensaver.pc.in
+++ b/xcb-screensaver.pc.in
@ -8,4 +8,4 @@ Description: XCB Screensaver Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-screensaver
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-shape.pc.in
+++ b/xcb-shape.pc.in
@ -8,4 +8,4 @@ Description: XCB Shape Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-shape
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-shm.pc.in
+++ b/xcb-shm.pc.in
@ -8,4 +8,4 @@ Description: XCB Shm Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-shm
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-sync.pc.in
+++ b/xcb-sync.pc.in
@ -8,4 +8,4 @@ Description: XCB Sync Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-sync
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xevie.pc.in
+++ b/xcb-xevie.pc.in
@ -8,4 +8,4 @@ Description: XCB Xevie Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-xevie
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xf86dri.pc.in
+++ b/xcb-xf86dri.pc.in
@ -8,4 +8,4 @@ Description: XCB XFree86-DRI Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-xf86dri
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xfixes.pc.in
+++ b/xcb-xfixes.pc.in
@ -8,4 +8,4 @@ Description: XCB XFixes Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-render xcb-shape
 Libs: -L${libdir} -lxcb-xfixes
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xinerama.pc.in
+++ b/xcb-xinerama.pc.in
@ -8,4 +8,4 @@ Description: XCB Xinerama Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-xinerama
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xinput.pc.in
+++ b/xcb-xinput.pc.in
@ -8,4 +8,4 @@ Description: XCB XInput Extension (EXPERIMENTAL)
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-xfixes
 Libs: -L${libdir} -lxcb-xinput
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xkb.pc.in
+++ b/xcb-xkb.pc.in
@ -8,4 +8,4 @@ Description: XCB Keyboard Extension (EXPERIMENTAL)
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-xkb
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xprint.pc.in
+++ b/xcb-xprint.pc.in
@ -8,4 +8,4 @@ Description: XCB Xprint Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-xprint
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xselinux.pc.in
+++ b/xcb-xselinux.pc.in
@ -8,4 +8,4 @@ Description: XCB SELinux Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-xselinux
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xtest.pc.in
+++ b/xcb-xtest.pc.in
@ -8,4 +8,4 @@ Description: XCB XTEST Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb
 Libs: -L${libdir} -lxcb-xtest
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xv.pc.in
+++ b/xcb-xv.pc.in
@ -8,4 +8,4 @@ Description: XCB Xv Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-shm
 Libs: -L${libdir} -lxcb-xv
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb-xvmc.pc.in
+++ b/xcb-xvmc.pc.in
@ -8,4 +8,4 @@ Description: XCB XvMC Extension
 Version: @PACKAGE_VERSION@
 Requires.private: xcb xcb-xv
 Libs: -L${libdir} -lxcb-xvmc
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@
--- a/xcb.pc.in
+++ b/xcb.pc.in
@ -10,4 +10,4 @@ Version: @PACKAGE_VERSION@
 Requires.private: @NEEDED@
 Libs: -L${libdir} -lxcb
 Libs.private: @LIBS@
-Cflags: -I${includedir}
+Cflags: -I${includedir} @XCB_CFLAGS@