I recall a change quite a while ago to save-and-restore the value of errno around XS calls, presumably to reduce the noise of XS calls changing the value of $!, presumably unintentionally.

But despite Net::SSLeay's pretty poor pass/fail ratio on CPAN of late, it does pass tests sometimes. That throws into question my recollection of this feature. Or perhaps it is the case that fairly rarely $! is 0 by luck and the test passes. Or perhaps this feature was only added on some platforms (and Net::SSLeay fails tests on other platforms for other reasons, of course).

But I certainly don't think your jumping to the conclusion of blaming compiler differences is warranted. I would not expect compiler differences to break linking of the errno global (if linking together global symbols didn't work, then you'd have a ton more problems than errno). And I wouldn't expect compiler difference to cause a change in how Perl deals with errno in some other way, though I'm less certain of that.

Update: Re^2: errno in XS not propagating to $! - breaks Net::SSLeay describes how there being two different errno globals can actually happen here.

My next step would be to search for code related to XS handling that sets errno.

I don't have anything resembling a solution, but I dimly remember having digged around in the same piece of code, while trying to come up with an explanation for another somewhat related problem  (though that was Net::SSLeay in combination with PAR::Packer — so read down a bit in the thread).  Unfortunately, as far as I can tell, the problem never got resolved... but maybe you'll find some additional pieces for the puzzle (if you haven't come across that thread already).  At least, it seems to confirm that - under some circumstances - something strange is happening with the errno values...  Good luck anyway!

SetLastError(ERROR_FILE_NOT_FOUND); instead of <code>errono=ENOENT;
SetLastError(ERROR_INVALID_DATA); instead of <code>errno=EINVAL;
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Note (probably harmless): No library found for -llibeay32MD
Note (probably harmless): No library found for -lssleay32MD
Note (probably harmless): No library found for -llibeay32
Note (probably harmless): No library found for -lssleay32
Note (probably harmless): No library found for -llibssl32
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The compiler that built ActivePerl and your compiler use different C runtime libraries - and that *can* definitely be nasty - though, mostly, it's not an issue. And I think it's quite possibly *not* an issue here.

I've confirmed that the perl.exe process has two CRTL DLLs loaded: msvcr71.dll (7.10.6030.0000) and msvcrt.dll (7.00.2600.2180).

I surmise that both of these export errno and perl58.dll is linking to one and the Net/SSLeay.dll is linking to the other. Thus setting errno in Net/SSLeay.dll does not alter the value of $! in Perl. Indeed now I write this I seem to recall having heard of this exact issue elsewhere.

Anyway, none of this will help you much - except perhaps for the notion that your problem lies with Test::Exception, rather than Net::SSLeay per se.

Thanks, but having placed diagnostic prints of errno and $! just before the and after the return from the XS code and I'm sure I've isolated (and circumvented) this problem. I think it will turn out to be the first of many getting Net::SSLeay to work (see Legacy use of splice() as lvalue).

Finally built Net-SSLeay-1.32 by replacing the existing Makefile.PL with

use ExtUtils::MakeMaker;

WriteMakefile(       
  NAME => 'Net::SSLeay',
  VERSION_FROM => 'lib/Net/SSLeay.pm',
);
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I then ran perl Makefile.PL INC="-IC:/path/to/ssl/include" LIBS="-LC:/path/to/ssl/lib -lssl -lcrypto" followed by dmake.

Because of the unusual directory structure of the test suite dmake test wouldn't run, so I opted to run the test suite by running perl -Mblib tests.txt where tests.txt contained:

use warnings;
use Test::Harness;

my @files = qw (
t/external/08_external.t
t/handle/external/10_destroy.t
t/handle/external/50_external.t
t/handle/local/05_use.t
t/local/00_ptr_cast.t
t/local/01_pod.t
t/local/02_pod_coverage.t
t/local/03_use.t
t/local/04_basic.t
t/local/05_passwd_cb.t
t/local/06_tcpecho.t
t/local/07_sslecho.t
t/local/08_pipe.t
t/local/15_bio.t
t/local/20_autoload.t
t/local/30_error.t
t/local/31_rsa_generate_key.t
t/local/35_ephemeral.t
t/local/50_digest.t
t/local/kwalitee.t
);

for(@files) {$_ = 'C:/_32/comp/Net-SSLeay-1.32/' . $_}

Test::Harness::runtests(@files);
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That throws up one error (test 3 of t/handle/external/10_destroy.t):

C:/_32/comp/Net-SSLeay-1.32/t/handle/external/10_destroy.....NOK 3#   
+Failed test
 'correct response'
#   at C:/_32/comp/Net-SSLeay-1.32/t/handle/external/10_destroy.t line
+ 36.
#                   undef
#     doesn't match '(?s-xim:^HTTP/1)'
C:/_32/comp/Net-SSLeay-1.32/t/handle/external/10_destroy.....ok 5/6# L
+ooks like you failed 1 test of 6.
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There were no other failures. Which test was failing for you ?

Cheers,
Rob