[Qemu-devel] [PATCH v2 0/4] configure: clang 3.5.0 build fixes

[Qemu-devel] [PATCH v2 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.

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):
  tricore: remove no-op abs() calls
  configure: silence glib unknown attribute __alloc_size__
  configure: Add workaround for ccache and clang

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

 configure                  | 48 +++++++++++++++++++++++++++++++++++++++++++++-
 target-tricore/op_helper.c | 12 ++++++------
 2 files changed, 53 insertions(+), 7 deletions(-)

-- 
2.1.0

[Qemu-devel] [PATCH v2 1/4] tricore: remove no-op abs() calls

[John Snow]

Calling abs() on a uint32_t is a no-op, so remove it.
clang 3.5.0 will not compile this if -Werror is set,
throwing a -Wabsolute-value warning.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 target-tricore/op_helper.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/target-tricore/op_helper.c b/target-tricore/op_helper.c
index 97b0c8b..5b82223 100644
--- a/target-tricore/op_helper.c
+++ b/target-tricore/op_helper.c
@@ -1953,9 +1953,9 @@ uint64_t helper_dvinit_b_13(CPUTriCoreState *env, uint32_t r1, uint32_t r2)
         quotient_sign = 1;
     }
 
-    abs_sig_dividend = abs(r1) >> 7;
-    abs_base_dividend = abs(r1) & 0x7f;
-    abs_divisor = abs(r1);
+    abs_sig_dividend = r1 >> 7;
+    abs_base_dividend = r1 & 0x7f;
+    abs_divisor = r1;
     /* calc overflow */
     env->PSW_USB_V = 0;
     if ((quotient_sign) && (abs_divisor)) {
@@ -2003,9 +2003,9 @@ uint64_t helper_dvinit_h_13(CPUTriCoreState *env, uint32_t r1, uint32_t r2)
         quotient_sign = 1;
     }
 
-    abs_sig_dividend = abs(r1) >> 7;
-    abs_base_dividend = abs(r1) & 0x7f;
-    abs_divisor = abs(r1);
+    abs_sig_dividend = r1 >> 7;
+    abs_base_dividend = r1 & 0x7f;
+    abs_divisor = r1;
     /* calc overflow */
     env->PSW_USB_V = 0;
     if ((quotient_sign) && (abs_divisor)) {
-- 
2.1.0

Re: [Qemu-devel] [PATCH v2 1/4] tricore: remove no-op abs() calls

[Peter Maydell]

On 18 March 2015 at 22:43, John Snow <jsnow@redhat.com> wrote:
> Calling abs() on a uint32_t is a no-op, so remove it.
> clang 3.5.0 will not compile this if -Werror is set,
> throwing a -Wabsolute-value warning.
>
> Signed-off-by: John Snow <jsnow@redhat.com>

This is probably the wrong fix (ie it silences the
warning rather than fixing the bug). See
http://patchwork.ozlabs.org/patch/447585/

thanks
-- PMM

Re: [Qemu-devel] [PATCH v2 1/4] tricore: remove no-op abs() calls

[John Snow]

On 03/18/2015 06:51 PM, Peter Maydell wrote:
> On 18 March 2015 at 22:43, John Snow <jsnow@redhat.com> wrote:
>> Calling abs() on a uint32_t is a no-op, so remove it.
>> clang 3.5.0 will not compile this if -Werror is set,
>> throwing a -Wabsolute-value warning.
>>
>> Signed-off-by: John Snow <jsnow@redhat.com>
>
> This is probably the wrong fix (ie it silences the
> warning rather than fixing the bug). See
> http://patchwork.ozlabs.org/patch/447585/
>
> thanks
> -- PMM
>

Ah, I missed that there was another patch out there and a deeper bug. I 
thought this was a harmless abs() inclusion, but I didn't look too 
deeply at it.

I am fine with dropping this patch if a more comprehensive change is in 
the works, but the other three should still stand.

--js

[Qemu-devel] [PATCH v2 2/4] 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 f74a6fd..062df84 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 v2 3/4] configure: silence glib unknown attribute __alloc_size__

[John Snow]

v2: We must test compilation with the right glib flags,
    otherwise the test compile will always fail.
    In addition, test-compile the warning flag to make
    sure we can use it.

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 that is the case.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: John Snow <jsnow@redhat.com>
---
 configure | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/configure b/configure
index 062df84..9db53ba 100755
--- a/configure
+++ b/configure
@@ -2784,6 +2784,21 @@ 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
+    cat > $TMPC << EOF
+    int main(void) { return 0; }
+EOF
+    if compile_prog "-Werror -Wunknown-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

Re: [Qemu-devel] [PATCH v2 3/4] configure: silence glib unknown attribute __alloc_size__

[Peter Maydell]

On 18 March 2015 at 22:43, John Snow <jsnow@redhat.com> wrote:
> v2: We must test compilation with the right glib flags,
>     otherwise the test compile will always fail.
>     In addition, test-compile the warning flag to make
>     sure we can use it.
>
> 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 that is the case.

Is it worth factoring out the body of the "see if we support
this long list of gcc warning flags?" check into a function?

cc_has_warning_flag () {
    # 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/')"
    compile_prog "-Werror $optflag" ""
}

and then

for flag in $gcc_flags; do
    if cc_has_warning_flag $flag
        QEMU_CFLAGS="$QEMU_CFLAGS $flag"
    fi
done

where we currently inline that sed/compile_prog. (Untested :-))

-- PMM

[Qemu-devel] [PATCH v2 4/4] configure: Add workaround for ccache and clang

[John Snow]

Test if ccache is interfering with our life, and
disable its habit of trying to compile already pre-processed
versions of code if so.

In particular, clang has different semantic warnings based on
if the warning arose from a macro or not. By trying to build
preprocessed versions of code, we get more errors than we should.

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.

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 | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/configure b/configure
index 9db53ba..f242181 100755
--- a/configure
+++ b/configure
@@ -4167,6 +4167,33 @@ if compile_prog "" "" ; then
     getauxval=yes
 fi
 
+########################################
+# check if ccache is interfering with
+# semantic analysis of macros
+
+ccache=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; then
+    ccache=yes
+fi
+
 ##########################################
 # End of CC checks
 # After here, no more $cc or $ld runs
@@ -5457,6 +5484,10 @@ if test "$numa" = "yes"; then
   echo "CONFIG_NUMA=y" >> $config_host_mak
 fi
 
+if test "$ccache" = "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