[Qemu-devel] [PATCH v4 0/4] configure: clang 3.5.0 build fixes

[Qemu-devel] [PATCH v4 0/4] configure: clang 3.5.0 build fixes

[John Snow]

QEMU does not compile cleanly under clang 3.5.0.  These patches eliminate the
avalanche of warnings and make the build usable.

v4:
- Enable ccache workaround for configurations without -Werror,
  to suppress warnings as well.
- Removed optimization from cc_has_warning_flag()
- Renamed ccache variable to ccache_cpp2

v3:
- Drop tricore patch, it's already being worked on elsewhere.
- Factor out flag check test.

v2:
 - Stole the series from Stefan
 - No changes to the -nopie patch, which I think was fine.
 - Fixed the -Wno-unknown-attributes patch.
 - Added a tricore fix for -Wabsolute-value
 - Added a workaround to help suppress ccache warnings

The result is that you *should* be able to use clang 3.5.0 *with* ccache and
-Werror and produce all targets.

John Snow (3):
  configure: factor out supported flag check
  configure: silence glib unknown attribute __alloc_size__
  configure: Add workaround for ccache and clang

Stefan Hajnoczi (1):
  configure: handle clang -nopie argument warning

 configure | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 65 insertions(+), 16 deletions(-)

-- 
2.1.0

[Qemu-devel] [PATCH v4 1/4] configure: handle clang -nopie argument warning

[John Snow]

From: Stefan Hajnoczi <stefanha@redhat.com>

gcc 4.9.2 treats -nopie as an error:

  cc: error: unrecognized command line option ‘-nopie’

clang 3.5.0 treats -nopie as a warning:

  clang: warning: argument unused during compilation: '-nopie'

The causes ./configure to fail with clang:

  ERROR: configure test passed without -Werror but failed with -Werror.

Make the -nopie test use -Werror so that compile_prog works for both gcc
and clang.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
---
 configure | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure b/configure
index 589798e..7a8637e 100755
--- a/configure
+++ b/configure
@@ -1589,7 +1589,7 @@ EOF
     fi
   fi
 
-  if compile_prog "-fno-pie" "-nopie"; then
+  if compile_prog "-Werror -fno-pie" "-nopie"; then
     CFLAGS_NOPIE="-fno-pie"
     LDFLAGS_NOPIE="-nopie"
   fi
-- 
2.1.0

[Qemu-devel] [PATCH v4 2/4] configure: factor out supported flag check

[John Snow]

Factor out the function that checks if a compiler
flag is supported or not.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 configure | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/configure b/configure
index 7a8637e..6f4bf4f 100755
--- a/configure
+++ b/configure
@@ -435,6 +435,12 @@ EOF
   compile_object
 }
 
+write_c_skeleton() {
+    cat > $TMPC <<EOF
+int main(void) { return 0; }
+EOF
+}
+
 if check_define __linux__ ; then
   targetos="Linux"
 elif check_define _WIN32 ; then
@@ -704,9 +710,7 @@ if test "$mingw32" = "yes" ; then
   # enable C99/POSIX format strings (needs mingw32-runtime 3.15 or later)
   QEMU_CFLAGS="-D__USE_MINGW_ANSI_STDIO=1 $QEMU_CFLAGS"
   LIBS="-lwinmm -lws2_32 -liphlpapi $LIBS"
-cat > $TMPC << EOF
-int main(void) { return 0; }
-EOF
+  write_c_skeleton;
   if compile_prog "" "-liberty" ; then
     LIBS="-liberty $LIBS"
   fi
@@ -1438,10 +1442,7 @@ if test -z "$werror" ; then
 fi
 
 # check that the C compiler works.
-cat > $TMPC <<EOF
-int main(void) { return 0; }
-EOF
-
+write_c_skeleton;
 if compile_object ; then
   : C compiler works ok
 else
@@ -1489,16 +1490,20 @@ gcc_flags="-Wno-string-plus-int $gcc_flags"
 # enable it for all configure tests. If a configure test failed due
 # to -Werror this would just silently disable some features,
 # so it's too error prone.
-cat > $TMPC << EOF
-int main(void) { return 0; }
-EOF
-for flag in $gcc_flags; do
+
+cc_has_warning_flag() {
+    write_c_skeleton;
+
     # Use the positive sense of the flag when testing for -Wno-wombat
     # support (gcc will happily accept the -Wno- form of unknown
     # warning options).
-    optflag="$(echo $flag | sed -e 's/^-Wno-/-W/')"
-    if compile_prog "-Werror $optflag" "" ; then
-	QEMU_CFLAGS="$QEMU_CFLAGS $flag"
+    optflag="$(echo $1 | sed -e 's/^-Wno-/-W/')"
+    compile_prog "-Werror $optflag" ""
+}
+
+for flag in $gcc_flags; do
+    if cc_has_warning_flag $flag --keep-tmpc; then
+        QEMU_CFLAGS="$QEMU_CFLAGS $flag"
     fi
 done
 
-- 
2.1.0

[Qemu-devel] [PATCH v4 3/4] configure: silence glib unknown attribute __alloc_size__

[John Snow]

The glib headers use GCC attributes.  Unfortunately the __GNUC__ and
__GNUC_MINOR__ version macros are also defined by clang, but clang
doesn't support the same attributes as GCC.

clang 3.5.0 does not support the __alloc_size__ attribute:

  https://github.com/llvm-mirror/clang/commit/c047507a9a79e89fc8339e074fa72822a7e7ea73

The following warning is produced:

  gstrfuncs.h:257:44: warning: unknown attribute '__alloc_size__' ignored [-Wunknown-attributes]
        G_GNUC_MALLOC G_GNUC_ALLOC_SIZE(2);
          gmacros.h:67:45: note: expanded from macro 'G_GNUC_ALLOC_SIZE'
                #define G_GNUC_ALLOC_SIZE(x) __attribute__((__alloc_size__(x)))

This patch checks whether glib headers cause warnings and disables
-Wunknown-attributes if it is able to.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
---
 configure | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/configure b/configure
index 6f4bf4f..87a7f40 100755
--- a/configure
+++ b/configure
@@ -2789,6 +2789,18 @@ if ! $pkg_config --atleast-version=2.38 glib-2.0; then
     glib_subprocess=no
 fi
 
+# Silence clang 3.5.0 warnings about glib attribute __alloc_size__ usage
+cat > $TMPC << EOF
+#include <glib.h>
+int main(void) { return 0; }
+EOF
+if ! compile_prog "$glib_cflags -Werror" "$glib_libs" ; then
+    if cc_has_warning_flag "-Wno-unknown-attributes"; then
+        glib_cflags="-Wno-unknown-attributes $glib_cflags"
+        CFLAGS="-Wno-unknown-attributes $CFLAGS"
+    fi
+fi
+
 ##########################################
 # SHA command probe for modules
 if test "$modules" = yes; then
-- 
2.1.0

[Qemu-devel] [PATCH v4 4/4] configure: Add workaround for ccache and clang

[John Snow]

Test if ccache is interfering with semantic analysis of macros,
disable its habit of trying to compile already pre-processed
versions of code if so. ccache attempts to save time by compiling
pre-processed versions of code, but this disturbs clang's static
analysis enough to produce false positives.

ccache allows us to disable this feature, opting instead to
compile the original version instead of its preprocessed version.
This makes ccache much slower for cache misses, but at least it
becomes usable with QEMU/clang.

This workaround only activates for users using ccache AND clang,
and only if their configuration is observed to be producing warnings.
You may need to clear your ccache for builds started without -Werror,
as those may continue to produce warnings from the cache.

Thanks to Peter Eisentraut for his writeup on the issue:
http://peter.eisentraut.org/blog/2014/12/01/ccache-and-clang-part-3/

Signed-off-by: John Snow <jsnow@redhat.com>
---
 configure | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index 87a7f40..36274cc 100755
--- a/configure
+++ b/configure
@@ -103,7 +103,8 @@ update_cxxflags() {
 }
 
 compile_object() {
-  do_cc $QEMU_CFLAGS -c -o $TMPO $TMPC
+  local_cflags="$1"
+  do_cc $QEMU_CFLAGS $local_cflags -c -o $TMPO $TMPC
 }
 
 compile_prog() {
@@ -4169,6 +4170,33 @@ if compile_prog "" "" ; then
     getauxval=yes
 fi
 
+########################################
+# check if ccache is interfering with
+# semantic analysis of macros
+
+ccache_cpp2=no
+cat > $TMPC << EOF
+static const int Z = 1;
+#define fn() ({ Z; })
+#define TAUT(X) ((X) == Z)
+#define PAREN(X, Y) (X == Y)
+#define ID(X) (X)
+int main(int argc, char *argv[])
+{
+    int x = 0, y = 0;
+    x = ID(x);
+    x = fn();
+    fn();
+    if (PAREN(x, y)) return 0;
+    if (TAUT(Z)) return 0;
+    return 0;
+}
+EOF
+
+if ! compile_object "-Werror"; then
+    ccache_cpp2=yes
+fi
+
 ##########################################
 # End of CC checks
 # After here, no more $cc or $ld runs
@@ -5461,6 +5489,10 @@ if test "$numa" = "yes"; then
   echo "CONFIG_NUMA=y" >> $config_host_mak
 fi
 
+if test "$ccache_cpp2" = "yes"; then
+  echo "export CCACHE_CPP2=y" >> $config_host_mak
+fi
+
 # build tree in object directory in case the source is not in the current directory
 DIRS="tests tests/tcg tests/tcg/cris tests/tcg/lm32 tests/libqos tests/qapi-schema tests/tcg/xtensa tests/qemu-iotests"
 DIRS="$DIRS fsdev"
-- 
2.1.0

Re: [Qemu-devel] [PATCH v4 2/4] configure: factor out supported flag check

[Stefan Hajnoczi]

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On Tue, Mar 24, 2015 at 02:19:44PM -0400, John Snow wrote:
> +cc_has_warning_flag() {
> +    write_c_skeleton;
> +
>      # Use the positive sense of the flag when testing for -Wno-wombat
>      # support (gcc will happily accept the -Wno- form of unknown
>      # warning options).
> -    optflag="$(echo $flag | sed -e 's/^-Wno-/-W/')"
> -    if compile_prog "-Werror $optflag" "" ; then
> -	QEMU_CFLAGS="$QEMU_CFLAGS $flag"
> +    optflag="$(echo $1 | sed -e 's/^-Wno-/-W/')"
> +    compile_prog "-Werror $optflag" ""
> +}
> +
> +for flag in $gcc_flags; do
> +    if cc_has_warning_flag $flag --keep-tmpc; then

Please drop the unused --keep-tmpc option here.

Stefan

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