[Bug target/47740] New: new specs function to avoid vxworks cross compiler requiring environment variable to compile

[richard_sharman at mitel dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47740

           Summary: new specs function to avoid vxworks cross compiler
                    requiring environment variable to compile
           Product: gcc
           Version: 4.4.5
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: target
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: richard_shar...@mitel.com


Created attachment 23343
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=23343
Patch for gcc/gcc.c gcc/config/vxworks.h gcc/doc/invoke.texi

I built a cross compiler for the powerpc-wrs-vxworks target,
configured as follows:

../configure  \
           --target=powerpc-wrs-vxworks  \
         --disable-multilib --with-endian=big  \
         --enable-languages="c,c++" \
         -with-headers=$WIND_BASE/target/h \
         --disable-multilib \
         --enable-threads=vxworks

This build copied the files specifed in the "-with-headers" to the directory
/usr/local/powerpc-wrs-vxworks/sys-include where the are found by the cross
compiler.

However,  what I found was that if I did *not* specify a value for the
environment variable WIND_BASE when compiling the cross compiler
failed.  If I set the value to anything, including an invalid
location such as /this/does/not/exist, then the compilation worked
fine.

The problem was that the specs file was outputting either 
-idirafter $(WIND_BASE )/target/h or  -idirafter $(WIND_USR)/h 
depending on whether the -mrtp option was given.

This might have been useful if the compiler had not already taken a
copy of the includes but isn't very useful as it is.  (It doesn't even
allow the use to override the built-in files by setting WIND_BASE
unless you also specify -nostdinc.)

There were two possible fixes:

1. Disable the getenv part of the specs completely.  (In retrospect I
think that would have been a better solution.  However, I went with #2.)

2. Add an alternate function that will substitute an environment
variable if it exists but does not produce an error if it does not
exist. 

Because the getenv function appears after the -idirafter I couldn't
simply have the function produce nothing if the variable wasn't set,
so I made the function have 3 arguments.   There is a prefix string,
the variable, and a suffix string.  If the variable is not set there
is no ouput.  If the variable is set the output is the concatenation
of the prefix string, the expanded variable and the suffix.  This
allows the -dirafter word to be specified as the prefix argument.

With this change, the specs file changes from

%{!nostdinc: %{isystem*} -idirafter %{mrtp: %:getenv(WIND_USR /h) ;:
%:getenv(WIND_BASE /target/h)}}

%{isystem*} %{mrtp: %:if-getenv(-idirafter\ WIND_USR /h) ;:
%:if-getenv(-idirafter\  WIND_BASE /target/h)}}

Attached is a context diff file.

Richard.