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libpng-config should filter out -L/usr/lib (or -L/usr/lib64) #206

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lemzwerg opened this issue Feb 10, 2018 · 0 comments

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commented Feb 10, 2018

Calling libpng-config --ldflags unconditionally emits -Lxxx, which is problematic. Consider a standard Unix installation with libraries in /usr/lib (or /usr/lib64), and local packages in /usr/local/lib (or /usr/local/lib64). It is quite common that the linker is set up to first look into /usr/local, then into /usr – this allows to provide newer, self-compiled library versions in the /usr/local tree.

If libpng-config installed in /usr is now called by a configure script, it emits -L/usr/lib (or -L/usr/lib64). Since -L prepends directories to the library search path, the linker no longer looks into /usr/local first for all libraries that follow, effectively hiding all newer library versions in /usr/local.

For this reason, /usr/lib and /usr/lib64 should always be filtered out. In case you want to stay with libpng-config at all (Debian gets rid of all *-config scripts soon), here is a possible patch.

--- libpng16-config.orig        2017-05-10 01:26:17.000000000 +0200
+++ libpng16-config     2018-02-10 20:30:06.195253267 +0100
@@ -25,6 +25,12 @@
 ccopts=""
 ldopts=""
 
+if test "${libdir}" = "/usr/lib" ||
+   test "${libdir}" = "/usr/lib64"; then
+  L_opts=""
+fi
+
+
 usage()
 {
     cat <<EOF
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