[Libguestfs] [PATCH 2/5] macosx: Add definition of program_name for gnulib

[Richard W.M. Jones]

On Mon, Feb 09, 2015 at 02:55:58PM +0000, Margaret Lewicka wrote:
> On 9 February 2015 at 13:10, Daniel P. Berrange <berrange at redhat.com> wrote:
> > On Mon, Feb 09, 2015 at 11:06:16AM +0000, Margaret Lewicka wrote:
> >> gnulib's error.c requires program_name to be externally defined
> >> for !_LIBC systems. This defines program_name for Darwin only.
> >> ---
> >>  configure.ac       | 3 +++
> >>  src/Makefile.am    | 6 ++++++
> >>  src/program_name.c | 4 ++++
> >>  3 files changed, 13 insertions(+)
> >>  create mode 100644 src/program_name.c
> >
> > src/guestfs-internal-frontend.h has a #define to replace use
> > of 'program_name' with something that is defined, so this
> > should not be required unless the header includes are not
> > right somewhere.
> 
> It is required, because gnulib itself explicitly defines an extern
> char *program_name. See gnulib/lib/error.c:118

What actually happens in gnulib's error.c is:

  #ifdef _LIBC
  /* In the GNU C library, there is a predefined variable for this.  */
  # define program_name program_invocation_name
  #endif

which on glibc causes all uses of `program_name' in the error.c source
to refer to refer to a string that glibc defines called
`program_invocation_name':

  extern char *program_invocation_name;  /* defined in glibc, same as argv[0]*/

On non-glibc, error.c says:

  /* The calling program should define program_name and set it to the
     name of the executing program.  */
  extern char *program_name;

This indicates to me that we shouldn't define `program_name' as a symbol
in libguestfs.  Instead every libguestfs-using program should define
it.  For example, virt-df (df/main.c) would have:

  #if /* this is Mac OS X */
  char *program_name = "virt-df";
  #endif

That sucks a lot.

I think the alternative is that you find a similar symbol defined by
Mac OS X that gives you the value of argv[0], and then send a patch to
gnulib which does:

  #if /* this is Mac OS X */
  #define program_name whatever_mac_os_x_defines_as_program_name
  #endif

My reading is that something like this might work, untested of course:

  #if /* this is Mac OS X */
  #define program_name (((char **)*_NSGetArgv())[0])
  #endif

Rich.

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