[PATCH v2 3/4] configure: do not clobber environment CFLAGS/CXXFLAGS/LDFLAGS

[Paolo Bonzini <pbonzini@redhat.com>]

If the CFLAGS, CXXFLAGS or LDFLAGS variables are present in the environment,
any modification made within the configure script is passed down to Meson.
This is particularly undesirable for the "-pie" option, since it overrides
"-shared" and thus messes up the linker flags for shared modules.

Using a separate variable therefore fixes the bug, while clarifying that
the scope of these CFLAGS is just the configure script.

Reported-by: Frederic Bezies
Analyzed-by: Toolybird
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 configure | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/configure b/configure
index b04350f7ea..d68a33e3c7 100755
--- a/configure
+++ b/configure
@@ -155,7 +155,7 @@ update_cxxflags() {
     # options which some versions of GCC's C++ compiler complain about
     # because they only make sense for C programs.
     QEMU_CXXFLAGS="$QEMU_CXXFLAGS -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS"
-    CXXFLAGS=$(echo "$CFLAGS" | sed s/-std=gnu99/-std=gnu++11/)
+    CONFIGURE_CXXFLAGS=$(echo "$CONFIGURE_CFLAGS" | sed s/-std=gnu99/-std=gnu++11/)
     for arg in $QEMU_CFLAGS; do
         case $arg in
             -Wstrict-prototypes|-Wmissing-prototypes|-Wnested-externs|\
@@ -170,13 +170,14 @@ update_cxxflags() {
 
 compile_object() {
   local_cflags="$1"
-  do_cc $CFLAGS $QEMU_CFLAGS $local_cflags -c -o $TMPO $TMPC
+  do_cc $CFLAGS $CONFIGURE_CFLAGS $QEMU_CFLAGS $local_cflags -c -o $TMPO $TMPC
 }
 
 compile_prog() {
   local_cflags="$1"
   local_ldflags="$2"
-  do_cc $CFLAGS $QEMU_CFLAGS $local_cflags -o $TMPE $TMPC $LDFLAGS $QEMU_LDFLAGS $local_ldflags
+  do_cc $CFLAGS $CONFIGURE_CFLAGS $QEMU_CFLAGS $local_cflags -o $TMPE $TMPC \
+      $LDFLAGS $CONFIGURE_LDFLAGS $QEMU_LDFLAGS $local_ldflags
 }
 
 # symbolically link $1 to $2.  Portable version of "ln -sf".
@@ -639,7 +640,10 @@ QEMU_CFLAGS="-Wstrict-prototypes -Wredundant-decls $QEMU_CFLAGS"
 QEMU_CFLAGS="-D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE $QEMU_CFLAGS"
 QEMU_INCLUDES="-iquote . -iquote ${source_path} -iquote ${source_path}/accel/tcg -iquote ${source_path}/include"
 QEMU_INCLUDES="$QEMU_INCLUDES -iquote ${source_path}/disas/libvixl"
-CFLAGS="-std=gnu99 -Wall"
+
+# Flags that are needed during configure but later taken care of by Meson
+CONFIGURE_CFLAGS="-std=gnu99 -Wall"
+CONFIGURE_LDFLAGS=
 
 
 check_define() {
@@ -967,7 +971,7 @@ if test "$mingw32" = "yes" ; then
   EXESUF=".exe"
   HOST_DSOSUF=".dll"
   # MinGW needs -mthreads for TLS and macro _MT.
-  CFLAGS="-mthreads $CFLAGS"
+  CONFIGURE_CFLAGS="-mthreads $CONFIGURE_CFLAGS"
   write_c_skeleton;
   prefix="/qemu"
   qemu_suffix=""
@@ -2234,7 +2238,7 @@ fi
 
 if test "$static" = "yes"; then
   if test "$pie" != "no" && compile_prog "-Werror -fPIE -DPIE" "-static-pie"; then
-    CFLAGS="-fPIE -DPIE $CFLAGS"
+    CONFIGURE_CFLAGS="-fPIE -DPIE $CONFIGURE_CFLAGS"
     QEMU_LDFLAGS="-static-pie $QEMU_LDFLAGS"
     pie="yes"
   elif test "$pie" = "yes"; then
@@ -2244,11 +2248,11 @@ if test "$static" = "yes"; then
     pie="no"
   fi
 elif test "$pie" = "no"; then
-  CFLAGS="$CFLAGS_NOPIE $CFLAGS"
-  LDFLAGS="$LDFLAGS_NOPIE $LDFLAGS"
+  CONFIGURE_CFLAGS="$CFLAGS_NOPIE $CONFIGURE_CFLAGS"
+  CONFIGURE_LDFLAGS="$LDFLAGS_NOPIE $CONFIGURE_LDFLAGS"
 elif compile_prog "-Werror -fPIE -DPIE" "-pie"; then
-  CFLAGS="-fPIE -DPIE $CFLAGS"
-  LDFLAGS="-pie $LDFLAGS"
+  CONFIGURE_CFLAGS="-fPIE -DPIE $CONFIGURE_CFLAGS"
+  CONFIGURE_LDFLAGS="-pie $CONFIGURE_LDFLAGS"
   pie="yes"
 elif test "$pie" = "yes"; then
   error_exit "PIE not available due to missing toolchain support"
@@ -3812,7 +3816,7 @@ 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"
+        CONFIGURE_CFLAGS="-Wno-unknown-attributes $CONFIGURE_CFLAGS"
     fi
 fi
 
@@ -3832,7 +3836,7 @@ EOF
 if ! compile_prog "$glib_cflags -Werror" "$glib_libs" ; then
     if cc_has_warning_flag "-Wno-unused-function"; then
         glib_cflags="$glib_cflags -Wno-unused-function"
-        CFLAGS="$CFLAGS -Wno-unused-function"
+        CONFIGURE_CFLAGS="$CONFIGURE_CFLAGS -Wno-unused-function"
     fi
 fi
 
@@ -6370,7 +6374,7 @@ EOF
 
     update_cxxflags
 
-    if do_cxx $CXXFLAGS $QEMU_CXXFLAGS -o $TMPE $TMPCXX $TMPO $QEMU_LDFLAGS; then
+    if do_cxx $CXXFLAGS $CONFIGURE_CXXFLAGS $QEMU_CXXFLAGS -o $TMPE $TMPCXX $TMPO $QEMU_LDFLAGS; then
         # C++ compiler $cxx works ok with C compiler $cc
         :
     else
-- 
2.26.2