Reconstructing an (SV *) when you know the address and the precise structure of the said SV

asarih has asked for the wisdom of the Perl Monks concerning the following question:

In XS:

Given an address in memory, is it possible to reconstruct an RV if you know exactly what it looks like (but none of the values)? The particular case that I am most interested in is a very simple reference to a reference, like so:

SV = RV(0x1f6394) at 0x31d968
  REFCNT = 2
  FLAGS = (ROK)
  RV = 0x2dfea0
[download]

The routine that will be reconstructing the RV will not know the values of the RV's (i.e., 0x1f6394 and 0x2dfea0 in the above example). Unfortunately, the pointer (say, ptr=0x31d968) is typecast to (char *), so if I simply look at sv_dump(*(SV **)ptr), I get something like:

SV = UNKNOWN(0x31) (0x0) at 0x31d968
  REFCNT = 0
  FLAGS = ()
[download]

Am I asking for the moon? I looked at perlapi and perlguts but couldn't quite figure it out. Apparently I don't know enough C tricks to pull this off. So, help me! Any help is appreciated.

Comment on Reconstructing an (SV *) when you know the address and the precise structure of the said SV Select or Download Code

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Re: Reconstructing an (SV *) when you know the address and the precise structure of the said SV by diotalevi (Canon) on Sep 19, 2003 at 03:44 UTC
Devel::Pointer. Neat module. Mostly I use it for stealing lexicals from out of scope locations. UPDATE: I also wrote Devel::Pointer::PP which is a bit more capable than the XS version and is pure perl instead of involving XS.	[reply]
Re: Reconstructing an (SV *) when you know the address and the precise structure of the said SV by idsfa (Vicar) on Sep 19, 2003 at 05:02 UTC
Can you cast ptr as a (void *) instead? This will prevent "helpful" attempts to understand the data. You seem to be wanting: `SV val = ((void )(ptr)); sv_dump(val);` [download] (The contents of the memory location specified by the contents of the memory location stored in ptr is a pointer to an SV) Or have I completely missed your question? Remember, when you stare long into the abyss, you could have been home eating ice cream.	[reply] [d/l]


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