That seems to work.

Aaah ... but it does matter in libdeflate-one.c, where free (and malloc) need to be implemented according to the stdlib.h specification, not according to perl's (re)definition of them. By undef'ing those 2 symbols, we ensure that the stdlib.h implementations are used.

Thank you for these insights.

I tried any number of things, but the

#undef malloc
[download]

idea was not one of them. I understand that XSUB.h or another Perl header file redefines malloc into a Perl function or macro which takes two arguments, but the thing which I still find confusing is that the error messages appear to be coming from XSUB.h yet the actual error is occurring within my C file libdeflate-one.c, so the error messages seem to assume that the error occurred on another line from where they actually did. Since the compiler is gcc it's not the fault of Microsoft Windows.

Edit

I have just spent a little time debugging another XS module on Strawberry Perl (for details see this diff) and I'd like to point out that

#undef realloc
[download]

and probably

#undef calloc
[download]

are also needed if the C code is using those as well.

There is no error message from Windows, and the GDB backtrace looks like this:

ok 1 - use Gzip::Zopfli;

Thread 1 received signal SIGSEGV, Segmentation fault.
0x00000000658f0794 in perl532!Perl_drand48_r () from C:\Strawberry\per
+l\bin\perl532.dll
(gdb) bt
#0  0x00000000658f0794 in perl532!Perl_drand48_r () from C:\Strawberry
+\perl\bin\perl532.dll
#1  0x0000000067948d63 in ?? () from C:\Users\ben\Documents\Gzip-Zopfl
+i-0.01\blib\arch\auto\Gzip\Zopfli\Zopfli.xs.dll
#2  0x000000006794985a in ?? () from C:\Users\ben\Documents\Gzip-Zopfl
+i-0.01\blib\arch\auto\Gzip\Zopfli\Zopfli.xs.dll
#3  0x0000000067949964 in ?? () from C:\Users\ben\Documents\Gzip-Zopfl
+i-0.01\blib\arch\auto\Gzip\Zopfli\Zopfli.xs.dll
#4  0x0000000067949bf4 in ?? () from C:\Users\ben\Documents\Gzip-Zopfl
+i-0.01\blib\arch\auto\Gzip\Zopfli\Zopfli.xs.dll
#5  0x000000006587b1e2 in perl532!Perl_clear_defarray () from C:\Straw
+berry\perl\bin\perl532.dll
#6  0x00000000658dfdd6 in perl532!Perl_runops_standard () from C:\Stra
+wberry\perl\bin\perl532.dll
#7  0x0000000065890eb7 in perl_run () from C:\Strawberry\perl\bin\perl
+532.dll
#8  0x00000000658f3ac8 in perl532!RunPerl () from C:\Strawberry\perl\b
+in\perl532.dll
#9  0x00000000004013c7 in ?? ()
#10 0x00000000004014fb in ?? ()
#11 0x00007ffe753d7034 in KERNEL32!BaseThreadInitThunk () from C:\WIND
+OWS\System32\kernel32.dll
#12 0x00007ffe764bd241 in ntdll!RtlUserThreadStart () from C:\WINDOWS\
+SYSTEM32\ntdll.dll
#13 0x0000000000000000 in ?? ()
Backtrace stopped: previous frame inner to this frame (corrupt stack?)
[download]

I found out what was wrong by Googling and puzzling over this bug report. It took a few attempts before I thought of this realloc problem.

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