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[PATCH] math/Makefile: don't clobber old libm.so on install [BZ #19822]


When installing glibc >= 2.22 in-place on a x86_64-pc-linux system with glibc
<= 2.21, the install will clobber the existing libm.so (e.g.,
/lib64/libm-2.21.so) with a linker script.  As a result, anything depending on
libm will fail to run (and running processes will segfault) and the install
fails.  This is because the makefile writes the linker script directly to
/lib64/libm.so.6, which is a symlink.

The simple patch below to math/Makefile fixes this.  It is based on the nptl
Makefile, which does exactly the same thing in a safer way.

I can confirm that without this patch a glibc 2.22 or 2.23 "make install"
renders my system unusable, but with it 2.23 installs just fine.  (I note that
by the time the install is finished, libm.so.6 is a symlink again, presumably
from ldconfig, so I'm not exactly sure why it's making a linker script.)

---
diff -u math/Makefile
--- a/math/Makefile	2016/02/18 17:54:00	1.1
+++ b/math/Makefile	2016/03/11 01:31:41
@@ -100,7 +100,8 @@
 	 cat $<; \
 	 echo 'GROUP ( $(slibdir)/libm.so$(libm.so-version) ' \
 	      'AS_NEEDED ( $(libdir)/libmvec_nonshared.a $(slibdir)/libmvec.so$(libmvec.so-version) ) )' \
-	) > $@
+	) > $@.new
+	mv -f $@.new $@
 endif
 
 # Rules for the test suite.


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