The -g and -O2 flags that configure adds to CFLAGS are only used by submodules,
so do not put anymore the confusing CFLAGS variable in config-host.mak and
replace it with more explicit SUBMODULE_CFLAGS variable.

There was also no equivalent SUBMODULE_LDFLAGS variable, add it.  This would
theoretically help with LTO if we want -g and -O2 options on the command line.
I say "theoretically" because submodules should not be linking anything; but
since we were passing an "LD" variable we might as well get its flags right.

CFLAGS are now synthesized in the configuration summary as a quick way to present
--enable-debug and --enable-debug-info.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Makefile    |  3 +--
 configure   | 13 +++++++++----
 meson.build |  3 ++-
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/Makefile b/Makefile
index 57fb63832f..3367ca520c 100644
--- a/Makefile
+++ b/Makefile
@@ -137,11 +137,10 @@ configure: ;
 .PHONY: all clean distclean install \
 	recurse-all dist msi FORCE
 
-SUBMODULE_CFLAGS = $(QEMU_CFLAGS) $(CFLAGS)
 SUBDIR_MAKEFLAGS = $(if $(V),,--no-print-directory --quiet)		\
 	PKG_CONFIG="$(PKG_CONFIG)" 					\
 	CC="$(CC)" AR="$(AR)" LD="$(LD)" RANLIB="$(RANLIB)"		\
-	CFLAGS="$(SUBMODULE_CFLAGS)" LDFLAGS="$(QEMU_LDFLAGS)"		\
+	CFLAGS="$(SUBMODULE_CFLAGS)" LDFLAGS="$(SUBMODULE_LDFLAGS)"	\
 	ARFLAGS="$(ARFLAGS)"
 
 include $(SRC_PATH)/tests/Makefile.include
diff --git a/configure b/configure
index ffc28e392f..5fabc77fb3 100755
--- a/configure
+++ b/configure
@@ -6108,12 +6108,16 @@ elif test "$fortify_source" = "yes" ; then
   QEMU_CFLAGS="-U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=2 $QEMU_CFLAGS"
   debug=no
 fi
+
+SUBMODULE_CFLAGS=-Wall
+SUBMODULE_LDFLAGS=
 if test "$debug_info" = "yes"; then
-  CFLAGS="-g $CFLAGS"
-  LDFLAGS="-g $LDFLAGS"
+  SUBMODULE_CFLAGS="$SUBMODULE_CFLAGS -g"
+  SUBMODULE_LDFLAGS="$SUBMODULE_LDFLAGS -g"
 fi
 if test "$debug" = "no"; then
-  CFLAGS="-O2 $CFLAGS"
+  SUBMODULE_CFLAGS="$SUBMODULE_CFLAGS -O2"
+  SUBMODULE_LDFLAGS="$SUBMODULE_LDFLAGS -O2"
 fi
 
 case "$ARCH" in
@@ -7288,7 +7292,8 @@ echo "RANLIB=$ranlib" >> $config_host_mak
 echo "NM=$nm" >> $config_host_mak
 echo "PKG_CONFIG=$pkg_config_exe" >> $config_host_mak
 echo "WINDRES=$windres" >> $config_host_mak
-echo "CFLAGS=$CFLAGS" >> $config_host_mak
+echo "SUBMODULE_CFLAGS=$CFLAGS \$(QEMU_CFLAGS) $SUBMODULE_CFLAGS" >> $config_host_mak
+echo "SUBMODULE_LDFLAGS=$LDFLAGS \$(QEMU_LDFLAGS) $SUBMODULE_LDFLAGS" >> $config_host_mak
 echo "CFLAGS_NOPIE=$CFLAGS_NOPIE" >> $config_host_mak
 echo "QEMU_CFLAGS=$QEMU_CFLAGS" >> $config_host_mak
 echo "QEMU_CXXFLAGS=$QEMU_CXXFLAGS" >> $config_host_mak
diff --git a/meson.build b/meson.build
index 1b1cde8725..1099f2a87c 100644
--- a/meson.build
+++ b/meson.build
@@ -1476,7 +1476,8 @@ if targetos == 'darwin'
   summary_info += {'Objective-C compiler': meson.get_compiler('objc').cmd_array()[0]}
 endif
 summary_info += {'ARFLAGS':           config_host['ARFLAGS']}
-summary_info += {'CFLAGS':            config_host['CFLAGS']}
+summary_info += {'CFLAGS':            '-O' + get_option('optimization')
+                                           + (get_option('debug') ? ' -g' : '')}
 summary_info += {'QEMU_CFLAGS':       config_host['QEMU_CFLAGS']}
 summary_info += {'QEMU_LDFLAGS':      config_host['QEMU_LDFLAGS']}
 summary_info += {'make':              config_host['MAKE']}
-- 
2.26.2

On 9/20/20 2:30 AM, Paolo Bonzini wrote:
> The -g and -O2 flags that configure adds to CFLAGS are only used by submodules,
> so do not put anymore the confusing CFLAGS variable in config-host.mak and
> replace it with more explicit SUBMODULE_CFLAGS variable.
> 
> There was also no equivalent SUBMODULE_LDFLAGS variable, add it.  This would
> theoretically help with LTO if we want -g and -O2 options on the command line.
> I say "theoretically" because submodules should not be linking anything; but
> since we were passing an "LD" variable we might as well get its flags right.
> 
> CFLAGS are now synthesized in the configuration summary as a quick way to present
> --enable-debug and --enable-debug-info.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

r~