Re: CVS commit: pkgsrc/net/libfetch

[John Marino <netbsd%marino.st@localhost>]

On 10/15/2012 17:40, Greg Troxel wrote:
> "John Marino"<marino%netbsd.org@localhost>  writes:
> > When building with gcc4.7, libfetch fails with the following error:
> >    ftp.c: In function 'unmappedaddr':
> >    ftp.c:149:2: error: dereferencing type-punned pointer will break
> >                 strict-aliasing rules [-Werror=strict-aliasing]
> >    cc1: all warnings being treated as errors
> >    *** Error code 1
> >
> > The code is intentionally grouping an array of four uint8_t bytes into a
> > uint32_t word.  Add -Wno-strict-aliasing in makefile to fix build in gcc4.7.
>
> But isn't the warning correct, in that dereferencing a uint32 pointer
> does not guarantee data coherency for objects of other types?  AIUI, in
> C99, the compiler is free to let objects of type other than foo have
> inconsistent values while a foo* is being dereferenced, and is only
> obligated to ensure consistency of objects of type foo.  It seems in
> modern C, one must use a union for such overlays.

Yes, the warning is correct.  That's why it had to be disabled.
To avoid a warning with strict-aliasing checking would require recoding. 
 That's a better long-term solution but I'll leave it to the 
maintainers of libfetch to determine if they want to rewrite the code.

John