[Nix-dev] Nix 0.13pre17232 doesn't work on i386-apple-darwin9.7.0

[Peter Simons]

Hi,

reportedly, some people have been able to install Nix on MacOS X. It is
a mystery to me how that might have worked. On my machine, Nix produces
a lot of errors during "make check":

 | installing `foo-1.0'
 | dyld: Symbol not found: _environ
 |   Referenced from: /tmp/nix-build-igvfiq0nxgvz6r50gxzdjgg0xa1ya0i5-nix-0.13pre17232.drv-0/nix-0.13pre17232/src/libutil/.libs/libutil.dylib
 |   Expected in: dynamic lookup
 |
 | error: unexpected EOF reading a line
 | FAIL: user-envs.sh

Dynamic libraries cannot access _environ on MacOS X. That pointer is
available only to executable programs, which is why the following code
in src/libutil/util.cc cannot work:

 | extern char * * environ;
 |
 | [...]
 |
 | void setuidCleanup()
 | {
 |     /* Don't trust the environment. */
 |     environ = 0;
 |
 |     [...]
 | }

The proper way to access _environ from a shared library is to obtain
that pointer at run-time from _NSGetEnviron(), which is defined in
<crt_externs.h>. (See "man environ" for additional detail.)

Furthermore, it's my experience on MacOS X that setting environ to NULL
is quite likely to cause core dumps. To avoid those, the pointer must be
set to a NULL-terminated array of char pointers, i.e.:

  static char * empty[] = { 0 };
  *_NSGetEnviron() = empty;

Anyway, fixing use of environ is trivial, but that only got me to the
next "make check" error that occurs because libutil.dylib cannot resolve
the global symbol 'ATempty' at load time.

I wonder how it's possible that I appear to be the only one who's
observing these problems?

Take care,
Peter