From XS code, I'd like to obtain the address of either the earliest allocated (lowest memory position) SV*, or some other address below which no memory will be dynamically allocated. Any suggestions of a variable accessible from XS code that fits the bill?

The reason is that some coderefs, for example *DynaLoader::, have links in their opcode chains (as traversed by Devel::Size), that are invalid: 

C:\Perl\packages\Devel-Size-X>perl -Mblib -MPOSIX -MDevel::Size=total_
+size 
-wle" print total_size( *DynaLoader:: )"
Devel::Size: Calculated sizes for compiled regexes are incompatible, a
+nd probably always will be
op_last:019D7014
baseop->op_next: 000000D5 ignored!
op_last:0189669C
baseop->op_next: 000000D3 ignored!
op_last:01892C7C
baseop->op_next: 00000084 ignored!
69229

[download]

In this case I have observed opcode->op_next with values of 0xD5, OxD3, Ox84. Whilst these are obviously erroneous, there are others like 0x00035ffe somewhere in *POSIX:: that look reasonable, but none the less point to pieces of virual memory that do not exist in the process address space, and so attempting to indirect through them is a walk into oblivion.

So my idea is to find some existing XS-accessible variable who's address is a reasonable lower bound below which D::S will not walk. Whilst this will not prevent all traps through uninitialised pointers, from observations, it would catch a large majority of those that I've seen.

Suggestions?

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In reply to [XS]:The address of the first dynamically allocated SV*? by BrowserUk

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