[Qemu-devel] [PATCH 2/3] kvm-userspace: kvmppc: fix hostlonbits detection when cross compiling v2

[ehrhardt@linux.vnet.ibm.com]

From: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>

*update*
further debugging according to some requests revealed that ARCH_CFLAGS does
not contain all CFLAGS that might be needed, especially those supplied via
extra-cflags. Therefore people supplying things via extra-cflags instead of an
environment variable might have had issues.

A recent kvm merge with qemu brought code for 64bit power that broke cross
compilation. The issue is caused by configure trying to execute target
architecture binaries where configure is executed.

I tried to change that detection so that it works with&without cross
compilation with only a small change and especially without an addtional
configure command line switch. Including the bits/wordsize.h header a platform
usually can check its wordsize and by doing that configure can check the
hostlongbits without executing the binary. Instead it now stops after
preprocessing stage which resolved the __WORDSIZE constant and retrieves
that value.

I don't like my new check style, but it is at least less broken than before.
Another approach that was suggested was that qemu might end up needing
something like asm-offsets in the kernel to manage architecture sizes etc.
Comments and other approaches welcome.
 
Signed-off-by: Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>
---

[diffstat]
 configure |   13 +++++++------
 1 file changed, 7 insertions(+), 6 deletions(-)

[diff]

diff --git a/qemu/configure b/qemu/configure
--- a/qemu/configure
+++ b/qemu/configure
@@ -685,14 +685,15 @@
 # ppc specific hostlongbits selection
 if test "$cpu" = "powerpc" ; then
     cat > $TMPC <<EOF
-int main(void){return sizeof(long);}
+#include <bits/wordsize.h>
+__WORDSIZE
 EOF
 
-    if $cc $ARCH_CFLAGS -o $TMPE $TMPC 2> /dev/null; then
-        $TMPE
-        case $? in
-            4) hostlongbits="32";;
-            8) hostlongbits="64";;
+    if $cc $ARCH_CFLAGS $CFLAGS -E -o $TMPE.E $TMPC 2> /dev/null; then
+        wordsize=`tail -n 1 ${TMPE}.E`
+        case $wordsize in
+            32) hostlongbits="32";;
+            64) hostlongbits="64";;
             *) echo "Couldn't determine bits per long value"; exit 1;;
         esac
     else