[Qemu-devel] [PATCH v2] configure: properly check if -lrt and -lm is needed

[Natanael Copa]

Fixes build against uClibc.

uClibc provides 2 versions of clock_gettime(), one with realtime
support and one without (this is so you can avoid linking in -lrt
unless actually needed). This means that the clock_gettime() don't
need -lrt. We still need it for timer_create() so we check for this
function in addition.

We also need check if -lm is needed for isnan().

Both -lm and -lrt are needed for libs_qga.

Signed-off-by: Natanael Copa <address@hidden>
---
The Xen people have nagged me to get this patch upstream so I have come
up with a rebased v2 patch after consulting with pm215 on IRC.

Please consider include this.

Changes v1->v2:
 - Check for sin() in addition to isnan()
 - Add comment on why we also check for timer_create
 - Use $LIBS and $libs_qga instead of $libm and $librt, based on
   feedback from pm215 on IRC
 - Do not remove the explicit add of -lm unless Haiku. This was due
   to http://www.mail-archive.com/address@hidden/msg102965.html
   I am not sure if this is valid, though.

 configure | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index edf9da4..a351f9b 100755
--- a/configure
+++ b/configure
@@ -2624,17 +2624,48 @@ fi
 
 
 ##########################################
+# Do we need libm
+cat > $TMPC << EOF
+#include <math.h>
+int main(void) { return isnan(sin(0.0)); }
+EOF
+if compile_prog "" "" ; then
+  :
+elif compile_prog "" "-lm" ; then
+  LIBS="-lm $LIBS"
+  libs_qga="-lm $libs_qga"
+else
+  echo
+  echo "Error: libm check failed"
+  echo
+  exit 1
+fi
+
+##########################################
 # Do we need librt
+# uClibc provides 2 versions of clock_gettime(), one with realtime
+# support and one without. This means that the clock_gettime() don't
+# need -lrt. We still need it for timer_create() so we check for this
+# function in addition.
 cat > $TMPC <<EOF
 #include <signal.h>
 #include <time.h>
-int main(void) { return clock_gettime(CLOCK_REALTIME, NULL); }
+int main(void) {
+  timer_create(CLOCK_REALTIME, NULL, NULL);
+  return clock_gettime(CLOCK_REALTIME, NULL);
+}
 EOF
 
 if compile_prog "" "" ; then
   :
 elif compile_prog "" "-lrt" ; then
   LIBS="-lrt $LIBS"
+  libs_qga="-lrt $libs_qga"
+else
+  echo
+  echo "Error: librt check failed"
+  echo
+  exit 1
 fi
 
 if test "$darwin" != "yes" -a "$mingw32" != "yes" -a "$solaris" != yes -a \
-- 
1.7.11.4