#2242 pointer acrobatics in sfcUtil/genericlist.c

[Klaus Kämpf]

Compiling sfccommon leads to lots of compiler warnings when compiling sfcUtil/genericlist.c
i.e.
sfcUtil/genericlist.c: In function 'listRelease':
sfcUtil/genericlist.c:556:3: warning: dereferencing type-punned pointer will break strict-aliasing rules

Patch follows ...

[Chris Buccella]

> Patch follows ...

Did you forget to attach it?

Also, I'm not seeing this warning when I compile. What gcc version are you using? I have 4.4.4 here.

[Klaus Kämpf]

Ah, sorry, the patch is not ready yet.

Compiler is gcc 4.5.1 with "-Wall"

[Klaus Kämpf]

Adapting summary to reflect root cause of the problem.

e.g. newList() does
UtilList ul;
initialize_list((Generic_list *) & ul.hdl);
and then initialize_list() continues with
list->info = ...

- the call to initialize_list casts a **void to Generic_list*
- the info element of Generic_list happens to be the first element (offset 0), just list hdr of UtilList
- thus by chance list->info dereferences to ul.hdr
- there's never a real pointer to a Generic_list, only to Generic_list.info. Luckily the static list manipulation functions only access list.info

[Klaus Kämpf]

Possible patch

[Klaus Kämpf]

Possible patch attached. Still ugly as it depends on ul.hdr and list.info being on offset 0.
Another fix is to set "-fno-strict-aliasing" in CFLAGS, but this would break optimization.

genericlist.c is up for a larger rewrite I guess ;-)