Thanks, that did help. The extra level of sub call/return allowed me to see the stack frame just before and after the trap occurs (in 5.8.8). It's happening as perl cleans up it's stack after the nested call; in Perl_free_temps(). It shows (I think), that the problem is nothing to do with GD but rather with the perl executable itself: 

PID: 320 TID: 1716 - Stack Contents for 0x280EAF30
0x280EAF30: perl58.dll:VMem::Free + 0x0054 <Void>
0x280EF62F: perl58.dll:CPerlHost::Free + 0x0021 <Void>
0x280EBE12: perl58.dll:PerlMemFree + 0x0016 <Void>
0x280E4E37: perl58.dll:Perl_safesysfree + 0x002A <Void>
0x280AEE3B: perl58.dll:Perl_sv_clear + 0x06EE <Void>
0x280AF2B0: perl58.dll:Perl_sv_free + 0x013E <Void>
0x280024D5: perl58.dll:Perl_av_undef + 0x008D <Void>
0x280AED0E: perl58.dll:Perl_sv_clear + 0x05C1 <Void>
0x280AF2B0: perl58.dll:Perl_sv_free + 0x013E <Void>
0x280350D8: perl58.dll:Perl_pad_undef + 0x0227 <Void>
0x280EF62F: perl58.dll:CPerlHost::Free + 0x0021 <Void>
0x2802CD37: perl58.dll:Perl_cv_undef + 0x0138 <Void>
0x280AECEA: perl58.dll:Perl_sv_clear + 0x059D <Void>
0x280AF2B0: perl58.dll:Perl_sv_free + 0x013E <Void>
0x280A2CEA: perl58.dll:Perl_free_tmps + 0x0077 <Void>
0x28065C6F: perl58.dll:Perl_pp_nextstate + 0x005F <op *>
0x280A26CD: perl58.dll:Perl_runops_standard + 0x000F <Int>
0x2803A9C5: perl58.dll:S_run_body + 0x018F <Void>
0x2803A562: perl58.dll:perl_run + 0x008A <Int>
0x280EEC9F: perl58.dll:RunPerl + 0x00A1 <Int>
0x7C0068F7: __getmainargs + 0x00BD
0x00401012: perl.exe:main + 0x0012 <Int>
0x0040115A: perl.exe:mainCRTStartup + 0x0143 <Int>
0x77E814C7: GetCurrentDirectoryW + 0x0044

[download]

In every other version I've traced, the stack is already corrupted by the time the trap occurs and so it was impossible to tell where I was in the code. I your version, the trap occurs much closer to the origin of the corruption and so the stack trace is still intact.

If I could get a version of the trap that didn't call GD at all would be the best demonstration, but maybe the above stacktrace is convincing when combined with the same code running clean under 5.8.6--which I will now re-install.

Thanks again for your help.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
Lingua non convalesco, consenesco et abolesco. -- Rule 1 has a caveat! -- Who broke the cabal?
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.

In reply to Re^2: Segfault on second (identical) call to a sub by BrowserUk
in thread Segfault on second (identical) call to a sub by BrowserUk

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