=back
-=head2 Common problems when patching Perl source code
-
-Perl source plays by ANSI C89 rules: no C99 (or C++) extensions. In
-some cases we have to take pre-ANSI requirements into consideration.
-You don't care about some particular platform having broken Perl?
-I hear there is still a strong demand for J2EE programmers.
-
-=head2 Perl environment problems
-
-=over 4
-
-=item *
-
-Not compiling with threading
-
-Compiling with threading (-Duseithreads) completely rewrites
-the function prototypes of Perl. You better try your changes
-with that. Related to this is the difference between "Perl_"-less
-and "Perl_-ly" APIs, for example:
-
- Perl_sv_setiv(aTHX_ ...);
- sv_setiv(...);
-
-The first one explicitly passes in the context, which is needed for
-e.g. threaded builds. The second one does that implicitly; do not get
-them mixed.
-
-See L<perlguts/"How multiple interpreters and concurrency are supported">
-for further discussion about context.
-
-=item *
-
-Not compiling with -DDEBUGGING
-
-The DEBUGGING define exposes more code to the compiler,
-therefore more ways for things to go wrong.
-
-=item *
-
-Not exporting your new function
-
-Some platforms (Win32, AIX, VMS, OS/2, to name a few) require any
-function that is part of the public API (the shared Perl library)
-to be explicitly marked as exported. See the discussion about
-F<embed.pl> in L<perlguts>.
-
-=item *
-
-Exporting your new function
-
-The new shiny result of either genuine new functionality or your
-arduous refactoring is now ready and correctly exported. So what
-could possibly be wrong?
-
-Maybe simply that your function did not need to be exported in the
-first place. Perl has a long and not so glorious history of exporting
-functions that it should not have.
-
-If the function is used only inside one source code file, make it
-static. See the discussion about F<embed.pl> in L<perlguts>.
-
-If the function is used across several files, but intended only for
-Perl's internal use (and this should be the common case), do not
-export it to the public API. See the discussion about F<embed.pl>
-in L<perlguts>.
-
-=back
-
-=head Portability problems
-
-The following are common causes of compilation and/or execution
-failures, not common to Perl as such. The C FAQ is good bedtime
-reading. Please test your changes with as many C compilers as
-possible -- we will, anyway, and it's nice to save oneself from
-public embarrassment.
-
-=over 4
-
-=item *
-
-Casting pointers to integers or casting integers to pointers
-
- void castaway(U8* p)
- {
- IV i = p;
-
-or
-
- void castaway(U8* p)
- {
- IV i = (IV)p;
-
-Either are bad, and broken, and unportable. Use the PTR2IV()
-macro that does it right. (Likewise, there are PTR2UV(), PTR2NV(),
-INT2PTR(), and NUM2PTR().)
-
-=item *
-
-Technically speaking casting between function pointers and data
-pointers is unportable and undefined, but practically speaking
-it seems to work, but you should use the FPTR2DPTR() and DPTR2FPTR()
-macros.
-
-=item *
-
-Assuming sizeof(int) == sizeof(long)
-
-There are platforms where longs are 64 bits, and platforms where ints
-are 64 bits, and while we are out to shock you, even platforms where
-shorts are 64 bits. This is all legal according to the C standard.
-(In other words, "long long" is not a portable way to specify 64 bits,
-and "long long" is not even guaranteed to be any wider than "long".)
-Use definitions like IVSIZE, I32SIZE, and so forth.
-
-=item *
-
-Assuming one can dereference any type of pointer for any type of data
-
- char *p = ...;
- long pony = *p;
-
-Many platforms, quite rightly so, will give you a core dump instead
-of a pony if the p happens not be correctly aligned.
-
-=item *
-
-Lvalue casts
-
- (int)*p = ...;
-
-Simply not portable. Get your lvalue to be of the right type,
-or maybe use temporary variables.
-
-=item *
-
-Using //-comments
-
- // This function bamfoodles the zorklator.
-
-That is C99 or C++. Perl is C89. Using the //-comments is silently
-allowed by many C compilers but cranking up the ANSI strictness (which
-we like to do) causes the compilation to fail.
-
-=item *
-
-Mixing declarations and code
-
- void zorklator()
- {
- int n = 3;
- set_zorkmids(n);
- int q = 4;
-
-That is C99 or C++. Some compilers allow that, but you shouldn't.
-
-=item *
-
-Mixing signed char pointers with unsigned char pointers
-
- int foo(char *s) { ... }
- ...
- unsigned char *t = ...; /* Or U8* t = ... */
- foo(t);
-
-While this is legal practice, it is certainly dubious, and downright
-fatal in at least one platform: for example VMS cc considers this a
-fatal error. One cause for people often making this mistake is that a
-"naked char" and therefore deferencing a "naked char pointer" have an
-undefined sign: it depends on the compilers and the platform whether
-the result is signed or unsigned.
-
-=item *
-
-Macros that have string constants and their arguments as substrings of
-the string constants
-
- #define FOO(n) printf("number = %d\n", n)
- FOO(10);
-
-Pre-ANSI semantics for that was equivalent to
-
- printf("10umber = %d\10");
-
-which is probably not what you were expecting. Unfortunately at
-least one C compiler does real backward compatibility here, in AIX
-that is what still happens even though the rest of the AIX compiler
-is very happily C89.
-
-=back
-
-=head2 Security problems
-
-Last but not least, here are various tips for safer coding.
-
-=over 4
-
-=item *
-
-Do not use gets()
-
-Or we will publicly ridicule you. Seriously.
-
-=item *
-
-Do not use strcpy() or strcat()
-
-Where there still linger some uses of these in the Perl source code,
-we have inspected them for safety and are very, very ashamed of them,
-and plan to get rid of them. In places where there are strlcpy()
-and strlcat() we prefer to use them, and there is a plan to integrate
-the strlcpy/strlcat implementation of INN.
-
-=item *
-
-Do not use sprintf() or vsprintf()
-
-Use my_snprintf() and my_vnsprintf() instead, which will try to use
-snprintf() and vsnprintf() if those safer APIs are available.
-
-=back
-
=head1 EXTERNAL TOOLS FOR DEBUGGING PERL
Sometimes it helps to use external tools while debugging and
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