[Qemu-devel] [PATCH v2] build: Use $(CCAS) for compiling .S files

[Qemu-devel] [PATCH v2] build: Use $(CCAS) for compiling .S files

[Richard Henderson]

We fail to pass to $(AS) all of the different flags that may be required
for a given set of CFLAGS.  Rather than figuring out the host-specific
mapping, it's better to allow the compiler driver to do that.

However, simply using $(CC) runs afoul of clang trying to build the
option roms.  C.f. 3dd46c78525a30e98c68, wherein we changed from
using $(CC) to using $(AS) in the first place.

Work around this by passing -fno-integrated-as to clang, so that we use
the external assembler, and the clang driver still passes along all of
the options that the assembler might require.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 configure | 13 ++++++++++---
 rules.mak |  7 ++-----
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/configure b/configure
index 5929aba..29ad43e 100755
--- a/configure
+++ b/configure
@@ -368,7 +368,7 @@ else
 fi
 
 ar="${AR-${cross_prefix}ar}"
-as="${AS-${cross_prefix}as}"
+ccas="${CCAS-$cc}"
 cpp="${CPP-$cc -E}"
 objcopy="${OBJCOPY-${cross_prefix}objcopy}"
 ld="${LD-${cross_prefix}ld}"
@@ -4488,6 +4488,13 @@ if test "$fortify_source" != "no"; then
   fi
 fi
 
+#################################################
+# clang does not support the 16-bit assembly for roms
+
+if echo | $ccas -dM -E - | grep __clang__ > /dev/null 2>&1 ; then
+  ccas="$ccas -fno-integrated-as"
+fi
+
 ##########################################
 # check if struct fsxattr is available via linux/fs.h
 
@@ -5498,7 +5505,7 @@ echo "CXX=$cxx" >> $config_host_mak
 echo "OBJCC=$objcc" >> $config_host_mak
 echo "AR=$ar" >> $config_host_mak
 echo "ARFLAGS=$ARFLAGS" >> $config_host_mak
-echo "AS=$as" >> $config_host_mak
+echo "CCAS=$ccas" >> $config_host_mak
 echo "CPP=$cpp" >> $config_host_mak
 echo "OBJCOPY=$objcopy" >> $config_host_mak
 echo "LD=$ld" >> $config_host_mak
@@ -5971,7 +5978,7 @@ for rom in seabios vgabios ; do
     config_mak=roms/$rom/config.mak
     echo "# Automatically generated by configure - do not modify" > $config_mak
     echo "SRC_PATH=$source_path/roms/$rom" >> $config_mak
-    echo "AS=$as" >> $config_mak
+    echo "CCAS=$ccas" >> $config_mak
     echo "CC=$cc" >> $config_mak
     echo "BCC=bcc" >> $config_mak
     echo "CPP=$cpp" >> $config_mak
diff --git a/rules.mak b/rules.mak
index 72c5955..7d7d83b 100644
--- a/rules.mak
+++ b/rules.mak
@@ -68,11 +68,8 @@ LINK = $(call quiet-command, $(LINKPROG) $(QEMU_CFLAGS) $(CFLAGS) $(LDFLAGS) -o
        $(call process-archive-undefs, $1) \
        $(version-obj-y) $(call extract-libs,$1) $(LIBS),"  LINK  $(TARGET_DIR)$@")
 
-%.asm: %.S
-	$(call quiet-command,$(CPP) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -o $@ $<,"  CPP   $(TARGET_DIR)$@")
-
-%.o: %.asm
-	$(call quiet-command,$(AS) $(ASFLAGS) -o $@ $<,"  AS    $(TARGET_DIR)$@")
+%.o: %.S
+	$(call quiet-command,$(CCAS) $(QEMU_INCLUDES) $(QEMU_CFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) -c -o $@ $<,"  AS    $(TARGET_DIR)$@")
 
 %.o: %.cc
 	$(call quiet-command,$(CXX) $(QEMU_INCLUDES) $(QEMU_CXXFLAGS) $(QEMU_DGFLAGS) $(CFLAGS) $($@-cflags) -c -o $@ $<,"  CXX   $(TARGET_DIR)$@")
-- 
2.5.5

Re: [Qemu-devel] [PATCH v2] build: Use $(CCAS) for compiling .S files

[Peter Maydell]

On 23 June 2016 at 18:39, Richard Henderson <rth@twiddle.net> wrote:
> We fail to pass to $(AS) all of the different flags that may be required
> for a given set of CFLAGS.  Rather than figuring out the host-specific
> mapping, it's better to allow the compiler driver to do that.
>
> However, simply using $(CC) runs afoul of clang trying to build the
> option roms.  C.f. 3dd46c78525a30e98c68, wherein we changed from
> using $(CC) to using $(AS) in the first place.
>
> Work around this by passing -fno-integrated-as to clang, so that we use
> the external assembler, and the clang driver still passes along all of
> the options that the assembler might require.
>
> Signed-off-by: Richard Henderson <rth@twiddle.net>

> +#################################################
> +# clang does not support the 16-bit assembly for roms
> +
> +if echo | $ccas -dM -E - | grep __clang__ > /dev/null 2>&1 ; then
> +  ccas="$ccas -fno-integrated-as"
> +fi

It would be neater to directly check whether assembling
the relevant constructs worked rather than just looking
for __clang__, but this works I guess.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM