Does XPUSHs make a copy of my_sv, or it really pushes my_sv into stack?

It really pushes it onto the stack. 

#define XPUSHs(s) STMT_START { EXTEND(sp,1); (*++sp = (s)); } STMT_END

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Your code has a memory leak, though. The scalar won't get freed since you didn't mortalise it, meaning you didn't tell Perl the stack owns a reference to it. 

SV* my_sv = newSViv(12345);
XPUSHs(sv_2mortal(my_sv));

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Same thing: 

SV* my_sv = newSViv(12345);
mXPUSHs(my_sv);

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It seems if I want to use the poped SV permanently (after FREETMPS and LEAVE), I have to make a copy of return by newSVsv(),

I think you can simple increase its REFCNT. If you do this, it's your responsibility to decrement its REFCNT when you're done with it.

Do I need to free the return manually, or it has been done automatically by FREETMPS and LEAVE?

You just have to call FREETMPS.

In reply to Re: What does perl stack OPs really do? by ikegami
in thread What does perl stack OPs really do? by llancet

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