I can confirm that you have to run
mine = Perl_get_context();

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before you can use this. The run of 
dSP;

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just segfaults if 
mine

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have not been set via 
mine = Perl_get_context();

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I call on initialisation of my module a XS function which does does do
mine = Perl_get_context();

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and verify that mine is not NULL before trying to call a perl function.

All I needed is the following to get it working, and call the function "functionname" within of the module I called "setcallback" from.
The use in C: 
void dorunperlfunction() {
   if (mine) {
      PERL_SET_CONTEXT(mine);
      dSP;
      ENTER;
      SAVETMPS;
      PUSHMARK(SP);
      PUTBACK;
      call_pv("functionname", G_DISCARD|G_NOARGS);
      FREETMPS;
      LEAVE;
   }

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The initialisation in XS(!): 
PerlInterpreter * mine = NULL;
...
void
setcallback()
   CODE:
      ...
      mine = Perl_get_context();
      ...

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In reply to Re^3: XS: Passing an external library's function a Perl XS callback by pRiVi
in thread SOLVED: XS: Passing an external library's function a Perl XS callback by stevieb

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