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Description of problem:
When using a relative topdir (eg when in a temporary rpm build space such as
through CVS), rpmbuild fails.

It attempts to cd /../BUILD which obviously doesn't exist.

It looks to me as if build/parsePrep.c is where this occurs

    /* cd to the build dir */
    {   const char * buildDirURL = rpmGenPath(spec->rootURL, "%{_builddir}", "");
        const char *buildDir;                                                  
                             
        (void) urlPath(buildDirURL, &buildDir);
...

The suspect function is rpmGenPath from rpmio/macro.c

if (root == NULL || *root == '\0') root = "/";

Which looks to be the culprit, I guess either you need to resolve relative paths
to put pwd in front or don't add a /

[paul@enki SPECS]$ rpmbuild --define '_topdir ..' -ba rpm.spec
Executing(%prep): /bin/sh -e /var/tmp/rpm-tmp.55384
+ umask 022
+ cd ../BUILD
+ LANG=C
+ export LANG
+ unset DISPLAY
+ cd /../BUILD
/var/tmp/rpm-tmp.55384: line 26: cd: /../BUILD: No such file or directory
error: Bad exit status from /var/tmp/rpm-tmp.55384 (%prep)
 
 
RPM build errors:
    Bad exit status from /var/tmp/rpm-tmp.55384 (%prep)



Version-Release number of selected component (if applicable):
rpm-4.2.1-0.30

How reproducible:
Always

Steps to Reproduce:
1. Go to a standard rpm build dir structure, go into SPECS subdir
2. rpmbuild --define '_topdir ..' foo.spec

    

Actual Results:  Prep fails with error as described

Expected Results:  rpm continues to build package normally

Additional info:

It's not in the macro processing:

rpm --define '_topdir ..' --eval='%{_builddir}'
../BUILD