mirror of
https://gitlab.uni-freiburg.de/opensourcevdi/spice-common
synced 2025-12-26 22:55:35 +00:00
858a0bfae9
For example, something like this:
uint8_t *p8;
uint32_t *p32 = (uint32_t *) p8;
generates a warning like this:
spice-channel.c:1350:10: error: cast from 'uint8_t *' (aka 'unsigned char *') to
'uint32_t *' (aka 'unsigned int *') increases required alignment from 1 to
4 [-Werror,-Wcast-align]
The warning indicates that we end up with a pointer to data that
should be 4-byte aligned, but its value may be misaligned. On x86,
this does not make much of a difference, except a relatively minor
performance penalty. However, on platforms such as older ARM, misaligned
accesses are emulated by the kernel, and support for them is optional.
So we may end up with a fault.
The intent of the fix here is to make it easy to identify and rework
places where actual mis-alignment occurs. Wherever casts raise the warning,
they are replaced with a macro:
- SPICE_ALIGNED_CAST(type, value) casts value to type, and indicates that
we believe the resulting pointer is aligned. If it is not, a runtime
warning will be issued. This check is disabled unless
--enable-alignment-checks is passed at configure time
- SPICE_UNALIGNED_CAST(type, value) casts value to type, and indicates that
we believe the resulting pointer is not always aligned.
Any code using SPICE_UNALIGNED_CAST may need to be revisited in order
to improve performance, e.g. by using memcpy.
There are normally no warnings for SPICE_UNALIGNED_CAST, but it is possible
to emit debug messages for mis-alignment in SPICE_UNALIGNED_CAST
by configuring with CFLAGS=-DSPICE_DEBUG_ALIGNMENT.
Signed-off-by: Christophe de Dinechin <dinechin@redhat.com>
73 lines
1.7 KiB
Plaintext
73 lines
1.7 KiB
Plaintext
AC_PREREQ([2.63])
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AC_INIT([spice-common],
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[noversion],
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[spice-devel@lists.freedesktop.org])
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AC_CONFIG_SRCDIR([common/bitops.h])
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AC_CONFIG_MACRO_DIR([m4])
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AM_CONFIG_HEADER([config.h])
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AC_CONFIG_AUX_DIR([build-aux])
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# For automake >= 1.12
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m4_ifdef([AM_PROG_AR], [AM_PROG_AR])
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# Checks for programs
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AM_INIT_AUTOMAKE([1.11 dist-xz no-dist-gzip tar-ustar foreign -Wall -Werror])
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AM_MAINTAINER_MODE
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AM_SILENT_RULES([yes])
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LT_INIT
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SPICE_MANUAL
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AC_PROG_CC
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AC_PROG_CC_C99
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if test "x$ac_cv_prog_cc_c99" = xno; then
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AC_MSG_ERROR([C99 compiler is required.])
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fi
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AM_PROG_CC_C_O
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SPICE_CHECK_SYSDEPS
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AC_ARG_ENABLE([alignment-checks],
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AS_HELP_STRING([--enable-alignment-checks],
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[Enable runtime checks for cast alignment @<:@default=no@:>@]),
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[],
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enable_alignment_checks="no")
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AS_IF([test "x$enable_alignment_checks" = "xyes"],
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[AC_DEFINE([SPICE_DEBUG_ALIGNMENT], 1, [Enable runtime checks for cast alignment])])
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# Checks for libraries
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PKG_CHECK_MODULES([PROTOCOL], [spice-protocol >= 0.12.12])
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SPICE_CHECK_PYTHON_MODULES()
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SPICE_CHECK_PIXMAN
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SPICE_CHECK_SMARTCARD
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SPICE_CHECK_CELT051
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SPICE_CHECK_GLIB2
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SPICE_CHECK_OPUS
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SPICE_CHECK_OPENSSL
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SPICE_COMMON_CFLAGS='$(PIXMAN_CFLAGS) $(SMARTCARD_CFLAGS) $(CELT051_CFLAGS) $(GLIB2_CFLAGS) $(OPUS_CFLAGS) $(OPENSSL_CFLAGS)'
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SPICE_COMMON_LIBS='$(PIXMAN_LIBS) $(CELT051_LIBS) $(GLIB2_LIBS) $(OPUS_LIBS) $(OPENSSL_LIBS)'
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AC_SUBST(SPICE_COMMON_CFLAGS)
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AC_SUBST(SPICE_COMMON_LIBS)
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# The End!
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AC_CONFIG_FILES([
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Makefile
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common/Makefile
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python_modules/Makefile
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tests/Makefile
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docs/Makefile
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])
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AH_BOTTOM([
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/* argh.. this is evil */
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#if defined(FIXME_SERVER_SMARTCARD) && defined(USE_SMARTCARD)
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%:undef USE_SMARTCARD
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#endif
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])
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AC_OUTPUT
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