RFC patch, 10 partsSparse: Git's "make check" target

Hi Junio,

Since the Git Makefile has a "check" target that uses sparse, I decided to take a look at the sparse project to see what it was about, and what it has to say about the git source code.

Initially, I had many problems because I am using cygwin, but I was able to fix most of those problems. (the output from "make check" was about 16k lines at one point!). Git also tickled a bug in sparse 0.2, which resulted in some 120+ lines of bogus warnings; that was fixed in version 0.3 (commit 0.2-15-gef25961). As a result, sparse version 0.3 + my patches, elicits 106 lines of output from "make check".

Naturally, I decided to "fix" the warnings produced by sparse, which resulted in the following patch series:

[PATCH 01/10] Sparse: fix "non-ANSI function declaration" warnings [PATCH 02/10] Sparse: fix some "using integer as NULL pointer" warnings [PATCH 03/10] Sparse: fix some "symbol not declared" warnings (Part 1) [PATCH 04/10] Sparse: fix some "symbol not declared" warnings (Part 2) [PATCH 05/10] Sparse: fix some "symbol not declared" warnings (Part 3) [PATCH 06/10] Sparse: fix "'add_head' not declared" warning [PATCH 07/10] Sparse: fix "'merge_file' not declared" warning [PATCH 08/10] Sparse: fix an "incorrect type in argument n" warning [PATCH 09/10] Sparse: fix some "symbol 's' shadows an earlier one" warnings [PATCH 10/10] Sparse: fix a "symbol 'weak_match' shadows an earlier one" warning

However, this patch series does not completely remove all warnings; the output is reduced to:

builtin-pack-objects.c:312:31: warning: Using plain integer as NULL pointer csum-file.c:152:22: warning: Using plain integer as NULL pointer exec_cmd.c:7:40: error: undefined identifier 'GIT_EXEC_PATH' git.c:209:35: error: undefined identifier 'GIT_VERSION' http.c:203:46: error: undefined identifier 'GIT_USER_AGENT' index-pack.c:201:25: warning: Using plain integer as NULL pointer index-pack.c:538:26: warning: Using plain integer as NULL pointer

The three "undefined identifier 'GIT_...'" are easy to remove, I just didn't get around to doing it (The GIT_... symbols are macros, defined in individual make rules rather than CFLAGS, an thus not passed to sparse).

The four "Using plain integer...", whilst equally easy to remove, arguably should
not be ;-)  If you look at the code you will find they are all of the form
    x = crc32(0, Z_NULL, 0);
where the second parameter type is basically (unsigned char *) and the Z_NULL
macro is defined in the zlib header file as 0.  It could be said that this is
"idiomatic zlib usage" and should remain as written.  If you don't subscribe
to that view, then the required patch is obvious :P)

The above is one reason why this is an RFC series. With one notable exception, the patches do not fix a bug, add a feature or alter the program behaviour. The only thing they do is remove sparse warnings; so you really have to believe that this is a worthwhile thing to do, otherwise they are worthless!

[Note: As far as the NULL pointer warnings are concerned, I don't much care either way. I just used that as an example (also note patch 02). Having said that, I do think that the "NULL is the only one true null pointer" brigade need to chill out a little; in fact I remember when 0 was the *only* null pointer.]

Another reason for the RFC, is that the patches are against the v1.5.2 tar-ball. Since this was released a few weeks ago, the patches may not apply cleanly to current git. (Yes, I really need to bite the bullet and get a broadband connection so that I can clone the git repo.)

Also, that "one notable exception" is patch 10, which fixes a bug caused by a "shadow" declaration. Unfortunately, it also crashes my laptop when running the test-suite. Yes, the machine freezes solid, with no option but to pull the power-cord, and then the battery ... (I blush to have to admit that it wasn't until the third time this happened that I realized that it might be an idea not to put the battery back ... ;-))

The first nine patches all pass "make test" no problem, but patch 10 causes totally unpredictable mayhem. The crash seems to occur randomly, on any test, even those which can't possibly be affected by the change (when have you heard that before...). As far as I can see, only git-http-push, git-send-pack and git-push should be affected, which in turn means only t5400-send-pack.sh, t5401-update-hooks.sh and t9400-git-cvsserver-server.sh. None of those tests have caused a crash. (actually, since I don't have cvs installed, t9400* is not even running)

The nature of the crash has made debugging this such a nightmare that I've just given up! Hopefully, somebody on a system which does not grind to a halt (ie. not using cygwin) can find the bug. (I think that cygwin may be part of the problem here)

If the patches are whitespace damaged, please let me know and I will resend as attachments. (As josh noticed on the sparse list, my thunderbird configuration was causing WS damage to the patches. I hope I have finally fixed that, but I can't guarantee it!)

I've included a few more notes below, if you want to reproduce the sparse output.

Hopefully someone will find this useful.

All the best,

Ramsay Jones

If you are on Linux and want to play along, then the official version 0.3 release of sparse should work for you, along with a minor change to the Makefile thus:

--->8---

Ramsay Jones wrote:

Glad to hear it!

One note about using Sparse with Git: you almost certainly don't want to pass -Wall to sparse, and current Git passes CFLAGS to Sparse which will do exactly that. -Wall turns on all possible Sparse warnings, including nitpicky warnings and warnings with a high false positive rate. You should start from the default set of Sparse warnings, and add additional warnings as desired, or turn off those you absolutely can't live with. Current Sparse from Git (post 0.3, after commit e18c1014449adf42520daa9d3e53f78a3d98da34) has a change to cgcc to filter out -Wall, so you can pass -Wall to GCC but not Sparse. See below for other reasons why you should use cgcc.

That said, this suggests that perhaps Sparse should treat -Wall differently for compatibility with GCC; specifically, perhaps Sparse should just ignore -Wall, as its meaning with GCC (enable a reasonable default set of warnings) already occurs by default in Sparse. The current -Wall could become something like -Weverything. This would make Sparse somewhat less intuitive, but somewhat more GCC compatible.

Awesome.  I'll take a look at that patch series.

You can easily fix that problem if you use cgcc as CC.

[...]

And at one point prototypes didn't exist either. :)

Other valid null pointers exist, such as (void *)0. You could also use (char *)0 in this particular case. Sparse complains because you just use the integer 0. I suggest just using NULL.

If you want to keep using Z_NULL rather than NULL, you could always undef it and define it as NULL after including the zlib header files.

If you really want to turn that particular Sparse warning off, you can use -Wno-non-pointer-null. However, I don't think you should do that.

Note that you could do that much more simply by using: gcc -E -dM -x c /dev/null | sed ...

However, see below about using cgcc instead.

Sparse has defined __STDC__ since 2003, well before even version 0.1.

Please go with that option. In addition to providing an easy way to use sparse and GCC together (make CC=cgcc), cgcc defines arch-specific flags that sparse currently does not. Ideally sparse should define these flags, but that would add some architecture-specific logic to sparse, which would then require sparse to know the desired machine target. That may need to happen in the future, but I don't have a good plan for how to do it yet. In the meantime, please run sparse through cgcc.

Also, you might consider just using cgcc to run both GCC and Sparse. That would handle the issue of target-specific CFLAGS, by ensuring that Sparse and GCC always see the same CFLAGS.

- Josh Triplett

Is this the recommended way? I that case I suggest that someone looks into the linux kernel part and change it to use this method.

	Sam

Sam Ravnborg wrote:

The approach taken by Linux allows running sparse on files without recompiling them. Using CC=cgcc just makes for less work, but the kernel has that work done now.

- Josh Triplett

Josh Triplett wrote:

I have to say that, my initial reaction, was to disagree; I certainly want to pass -Wall to sparse! Why not? Did you have any particular warnings in mind? (I haven't noticed any that were nitpicky or had a high false positive rate!)

...  You should start from

Why not "-Wall -Wno-nitpicky -Wno-false-positive" ;-)

... Current Sparse from Git (post

Yes, I noticed that. Again, I'm not sure I agree. I didn't comment on that patch, because my exposure to sparse is very limited. So far I've only run it on git, so I can hardly claim any great experience with the output from sparse. However, 105 lines of output (which represents 71 warnings) for 72,974 lines of C (in 179 .c files) did not seem at all unreasonable.

Yes, but that was actually an improvement to the language ;-)

(As I say above, I don't really care about the NULL pointer example; I hope the main point was not lost)

All the Best,

Ramsay Jones

Ramsay Jones wrote:

If you don't mind the set of warnings you get, then sure, use -Wall.

Some of the ones I had in mind:
* -Wshadow.  Not everyone cares.
* -Wptr-subtraction-blows.  This warns any time you do ptr2 - ptr1.
* -Wundefined-preprocessor.  This warns if you ever do
  #if SYMBOL
  when SYMBOL might not actually have a definition.  Many projects do exactly
  that, and the C standard allows it.
* -Wtypesign.  Off by default for the same reason that GCC doesn't give sign
   mismatches by default: too many codebases with too many sloppy signedness
   issues that drown out other issues.

If you don't mind that, then sure. You might have to adjust the warning list to taste from time to time. But please do use -Wall if you feel comfortable with the warnings it produces.

True; for a project the size of Git, you can reasonably handle all the warnings as you did.

If you want to use -Wall with sparse, you can always pass -Wall to sparse directly, or use CHECK="sparse -Wall" cgcc.

- Josh Triplett