Commit fd0e6053 authored by John Snow's avatar John Snow Committed by Stefan Hajnoczi
Browse files

configure: Add workaround for ccache and clang 

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: default avatarJohn Snow <jsnow@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Message-id: 1427324259-1481-5-git-send-email-jsnow@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent bbbf2e04

configure

+33 −1
Original line number Diff line number Diff line
@@ -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() {
@@ -4209,6 +4210,33 @@ 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 $ld runs
@@ -5502,6 +5530,10 @@ if test "$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"