Silence uninitialized compiler warnings in libbzip2

[demerphq <demerphq@gmail.com>]

Hi,

I am a contributor to the Perl project. https://github.com/Perl/perl5

We bundle your library libbzip2 via the perl Module Compress-Raw-Bzip2,
which is hosted at:

https://github.com/pmqs/Compress-Raw-Bzip2

We are trying to ensure our builds are warning clean, however when building
this package your library produces "may be used uninitialized" warnings on
some compilers, you can see these warnings below.

While this is almost certainly a false positive warning, it is also trivial
to silence the warnings with essentially no performance hit by initializing
the cost structure with 0's at the start.

We have an open bug report for this for perl here:
https://github.com/Perl/perl5/issues/19432

And an open bug report for this for the module here:
https://github.com/pmqs/Compress-Raw-Bzip2/issues/4

And a patch for it here:
https://github.com/pmqs/Compress-Raw-Bzip2/pull/5/commits/641a440ec6229c1d368b9ead48f4968b955c0115

The maintainer of Compress-Raw-Bzip2 (on CC) is known to prefer not to
apply changes to this library code that are not upstream. (A reasonable
policy.)

I was wondering if you could apply this patch, or something equivalent that
would fix this so that the perl project could have warning free builds.
Your library is the last module we ship that produces warnings during the
build process. We target a wide range of compilers and try to keep our code
as clean as possible, and while again I accept that your code likely is not
buggy as you initialize it in a loop at line 357,

357:         for (t = 0; t < nGroups; t++) cost[t] = 0;

as far as I can tell nGroups is not a constant, and the compiler reasonably
cannot be certain that all BZ_N_GROUPS entries in the array are initialized
before use.

We in the perl development community would appreciate it if you would
release a patch that would silence these warnings for us. Then Paul could
roll a new release of his module, and we in the Perl could then use that
and be happy with a completely warning free build.

gcc -c  -I. -D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing
-pipe -fstack-protector-strong -I/usr/local/include
-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -Wall -Werror=pointer-arith
-Werror=vla -Wextra -Wno-long-long -Wno-declaration-after-statement
-Wc++-compat -Wwrite-strings -O3   -DVERSION=\"2.101\"
-DXS_VERSION=\"2.101\" -fPIC "-I../.."  -Wall -Wno-comment
-DBZ_NO_STDIO  compress.c
compress.c: In function ‘BZ2_compressBlock’:
compress.c:392:54: warning: ‘cost[5]’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
                for (t = 0; t < nGroups; t++) cost[t] += s->len[t][icv];
                                                      ^~
compress.c:256:11: note: ‘cost[5]’ was declared here
    UInt16 cost[BZ_N_GROUPS];
           ^~~~
compress.c:402:21: warning: ‘cost[3]’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
             if (cost[t] < bc) { bc = cost[t]; bt = t; };
                 ~~~~^~~
compress.c:256:11: note: ‘cost[3]’ was declared here
    UInt16 cost[BZ_N_GROUPS];
           ^~~~
compress.c:402:21: warning: ‘cost[2]’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
             if (cost[t] < bc) { bc = cost[t]; bt = t; };
                 ~~~~^~~
compress.c:256:11: note: ‘cost[2]’ was declared here
    UInt16 cost[BZ_N_GROUPS];
           ^~~~

Your consideration on this matter would be much appreciated.

I have requested an account with your bug tracker and will file a formal
ticket as soon as I get an account.

Thank you very much for your time in producing this library, I
personally have made use of it many times in my career.

cheers,
Yves

-- 
perl -Mre=debug -e "/just|another|perl|hacker/"