RFR: JDK-8055141 Catch linker errors earlier in the JVM build by not allowing unresolved externals

Mikael Gerdin mikael.gerdin at oracle.com
Thu Sep 18 08:39:57 UTC 2014

Hi all,

As you may know, linking an ELF shared object allows unresolved external 
symbols at link time. This is sometimes problematic for JVM developers since 
the JVM does not depend on unresolved external symbols and all missing symbols 
at build time are due to mistakes, usually missing includes of inline 

In order to disallow such unresolved externals I propose that we add
"-z defs" to the linker command line when linking the JVM, thereby making 
unresolved externals a build-time error instead of a run-time failure when 
dlopen:ing the newly built JVM for the first time.

On Windows ans OSX this is already the default linker behavior.
I took the liberty of modifying the bsd make file since I believe that bsd 
uses the GNU linker which supports the "-z defs" flag. I'm not sure about the 
behavior or flags appropriate for AIX so I didn't change the AIX makefiles.

On Solaris, linking with "-z defs" failed at first with the following message:

Undefined                       first referenced
 symbol                             in file
gethostbyname                       ostream.o  (symbol belongs to implicit 
dependency /lib/64/libnsl.so.1)
inet_addr                           ostream.o  (symbol belongs to implicit 
dependency /lib/64/libnsl.so.1)
ld: fatal: symbol referencing errors. No output written to libjvm.so

This has not caused any failures earlier since libsocket depends on libnsl, so 
in practice the symbols are always present at runtime, but with the "-z defs" 
flag the linker requires the dependency to be explicitly stated.
I fixed the issure by appending -lnsl to the link-time libraries for the 
Solaris build.

Webrev: http://cr.openjdk.java.net/~mgerdin/8055141/webrev.0/
Bug: https://bugs.openjdk.java.net/browse/JDK-8055141

* Verified that the additional flag causes build-time errors on all platforms 
in the presence of unresolved external symbols.
* Verified that the build passes on all Oracle-supported platforms with the 
new flag.


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