[PATCH] Fix an unitialized pointer in merge-recursive.c

[PATCH] Fix an unitialized pointer in merge-recursive.c

[Marco Costalba]

Indeed &mrtree is passed to merge_trees() that not always
seems to set the value, so on some paths mrtree could
return uninitialized.

Spotted by a gcc 4.2.1 warning

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
---
 merge-recursive.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/merge-recursive.c b/merge-recursive.c
index 16f6a0f..934b0d6 100644
--- a/merge-recursive.c
+++ b/merge-recursive.c
@@ -1610,7 +1610,7 @@ static int merge(struct commit
 {
  	struct commit_list *iter;
  	struct commit *merged_common_ancestors;
-	struct tree *mrtree;
+	struct tree *mrtree = NULL;
 	int clean;

 	if (show(4)) {
-- 
1.5.3.rc4.67.gf9286

Re: [PATCH] Fix an unitialized pointer in merge-recursive.c

[Junio C Hamano]

"Marco Costalba" <mcostalba@gmail.com> writes:

> Indeed &mrtree is passed to merge_trees() that not always
> seems to set the value, so on some paths mrtree could
> return uninitialized.
>
> Spotted by a gcc 4.2.1 warning

Are you sure that gcc is correctly seeing the codeflow?

In merge(), mrtree is used only under index_only, and
merge_trees() always sets *result under index_only.

Re: [PATCH] Fix an unitialized pointer in merge-recursive.c

[Marco Costalba]

On 8/16/07, Junio C Hamano <gitster@pobox.com> wrote:
> "Marco Costalba" <mcostalba@gmail.com> writes:
>
> > Indeed &mrtree is passed to merge_trees() that not always
> > seems to set the value, so on some paths mrtree could
> > return uninitialized.
> >
> > Spotted by a gcc 4.2.1 warning
>
> Are you sure that gcc is correctly seeing the codeflow?
>
> In merge(), mrtree is used only under index_only, and
> merge_trees() always sets *result under index_only.
>

Ok ;-)

Now two options:

- discard the patch

- change the title in 'silence a gcc bougus warning'

Re: [PATCH] Fix an unitialized pointer in merge-recursive.c

[Junio C Hamano]

"Marco Costalba" <mcostalba@gmail.com> writes:

> On 8/16/07, Junio C Hamano <gitster@pobox.com> wrote:
>> "Marco Costalba" <mcostalba@gmail.com> writes:
>>
>> > Indeed &mrtree is passed to merge_trees() that not always
>> > seems to set the value, so on some paths mrtree could
>> > return uninitialized.
>> >
>> > Spotted by a gcc 4.2.1 warning
>>
>> Are you sure that gcc is correctly seeing the codeflow?
>>
>> In merge(), mrtree is used only under index_only, and
>> merge_trees() always sets *result under index_only.
>>
>
> Ok ;-)
>
> Now two options:
>
> - discard the patch
>
> - change the title in 'silence a gcc bougus warning'

Third option.  Change the assignment from "mrtree = NULL" to
"mrtree = mtree".  It is a standard idiom to work around stupid
gcc warnings.

Re: [PATCH] Fix an unitialized pointer in merge-recursive.c

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> Third option.  Change the assignment from "mrtree = NULL" to
> "mrtree = mtree".  It is a standard idiom to work around stupid
> gcc warnings.

Oops; it might be obvious but that's "mrtree = mrtree".

Re: [PATCH] Fix an unitialized pointer in merge-recursive.c

[David Kastrup]

Junio C Hamano <gitster@pobox.com> writes:

> "Marco Costalba" <mcostalba@gmail.com> writes:
>
>> On 8/16/07, Junio C Hamano <gitster@pobox.com> wrote:
>>> "Marco Costalba" <mcostalba@gmail.com> writes:
>>>
>>> > Indeed &mrtree is passed to merge_trees() that not always
>>> > seems to set the value, so on some paths mrtree could
>>> > return uninitialized.
>>> >
>>> > Spotted by a gcc 4.2.1 warning
>>>
>>> Are you sure that gcc is correctly seeing the codeflow?
>>>
>>> In merge(), mrtree is used only under index_only, and
>>> merge_trees() always sets *result under index_only.
>>
>> Ok ;-)
>>
>> Now two options:
>>
>> - discard the patch
>>
>> - change the title in 'silence a gcc bougus warning'
>
> Third option.  Change the assignment from "mrtree = NULL" to
> "mrtree = mtree".  It is a standard idiom to work around stupid
> gcc warnings.

I think it is more efficient to write mrtree = NULL: For the computer,
it makes a minuscule difference, and it can save programmers a bit of
confusion and worrying times.  Time that may be better spent improving
things elsewhere.

I don't think that we have a contest running for least redundancy in
code layout, have we?  Why then require the programmer to do a
complete call trace analysis before he can feel comfortable about the
code?  And what if callers change at some point of time?

-- 
David Kastrup

Re: [PATCH] Fix an unitialized pointer in merge-recursive.c

[Florian Weimer]

* Junio C. Hamano:

> Third option.  Change the assignment from "mrtree = NULL" to
> "mrtree = mtree".  It is a standard idiom to work around stupid
> gcc warnings.

Is it?  It's also undefined according to the C standard.  In other
words, the compiler may assume that this particular declaration is
never reached.