Shame it doesn't work with my compiler :(

Actually doing the expansion isn't hard:

C:\test>type expand_malloc.c
#include "EXTERN.h"
#include "perl.h"

char *p = malloc( 10 );

C:\test> cl -E -nologo -GF -W3 -MD -Zi -DNDEBUG -Ox -GL -Wp64 -fp:prec
+ise -DWIN32 -D_CONSOLE -DNO_STRICT -DHAVE_DES_FCRYPT -DWIN64 -DCONSER
+VATIVE -DUSE_SITECUSTOMIZE -DPRIVLIB_LAST_IN_INC -DPERL_IMPLICIT_CONT
+EXT -DPERL_IMPLICIT_SYS -DUSE_PERLIO -DPERL_MSVCRT_READFIX -MD -Zi -D
+NDEBUG -Ox -GL -Wp64 -fp:precise    -DVERSION=\"1.76\"  -DXS_VERSION=
+\"1.76\"  "-IC:\Perl64\lib\CORE"  -DHAS_PPPORT_H expand_malloc.c >jun
+k.txt
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And if you load up the output file junk.txt, and wade you way down to line: 203,525 (Yes! That really is line: two hundred and three thousand five hundred and twenty five!), you get:

[203524 lines omitted :)]
#line 3 "expand_malloc.c"

char *p = malloc( 10 );
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which probably means I've got the wrong set of defines on the command line :(

Update: Of course. I forgot to include XSUB.h:

...
#line 4 "expand_malloc.c"

char *p = (*(*Perl_IMem_ptr(((PerlInterpreter *)Perl_get_context())))-
+>pMalloc)((*Perl_IMem_ptr(((PerlInterpreter *)Perl_get_context()))), 
+(10));
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