you do nothing to upgrade the bare SV to be of sufficient type to hold a PV

According to the docs:

newSV

Creates a new SV. A non-zero len parameter indicates the number of bytes of preallocated string space the SV should have. An extra byte for a trailing NUL is also reserved. (SvPOK is not set for the SV even if string space is allocated.) The reference count for the new SV is set to 1.

Which kind of implies that it creates a PV-type SV -- given that it offers to preallocate some space to the PV.

But I guess that it just fails to mention that if you give a zero parameter, not only does it not preallocate the space, it doesn't allocate the PV-type fields either :(

perhaps you are building in an environment that doesn't have assert()s enabled.

You're right. I had the session configured for /release instead of /debug.

the ref you return on the stack is not mortalized

I believe I::C will take care of that for me.

Ah. I was reading code not documentation. :)

SV *
Perl_newSV(pTHX_ const STRLEN len)
{
    dVAR;
    register SV *sv;

    new_SV(sv);
    if (len) {
        sv_upgrade(sv, SVt_PV);
        SvGROW(sv, len + 1);
    }
    return sv;
}
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I believe I::C will take care of that for me.

Indeed. Inline::C-Cookbook makes that clear (though doesn't take the credit):

In this example the sv_2mortal call gets done under the hood by XS, because we declared the return type to be SV*.

Thanks.

- tye        

Which kind of implies that it creates a PV-type SV

...when given "a non-zero len parameter", which doesn't apply to your code. You have a gave a zero len parameter, for which its documentation only says it "Creates a new SV." It creates the most basic of SVs:

use Inline C => <<'__EOI__';

void testing() {
   SV* sv = newSV(0);
   sv_dump(sv);
   SvREFCNT_dec(sv);
}

__EOI__

testing();
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SV = NULL(0x0) at 0x8eec248
  REFCNT = 1
  FLAGS = ()
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This creates a PV:

newSVpvn("", 0)
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I believe I::C will take care of that for me.

Yes, though it's actually XS by means of the typemap that does it.