On 08/12/2013 07:46 AM, Junio C Hamano wrote:
> Jeff King <peff@xxxxxxxx> writes:
>
>> On Thu, Aug 08, 2013 at 08:31:44PM +0200, Stefan Beller wrote:
>>
>>> The next occurrences are at:
>>> /* Never use a non-valid filename anywhere if at all possible */
>>> name_a = DIFF_FILE_VALID(one) ? name_a : name_b;
>>> name_b = DIFF_FILE_VALID(two) ? name_b : name_a;
>>>
>>> a_one = quote_two(a_prefix, name_a + (*name_a == '/'));
>>> b_two = quote_two(b_prefix, name_b + (*name_b == '/'));
>>>
>>> In the last line of this block 'name_b' is dereferenced and compared
>>> to '/'. This would crash if name_b was NULL. Hence in the following code
>>> we can assume name_b being non-null.
>>
>> I think your change is correct, but I find the reasoning above a little
>> suspect. It assumes that the second chunk of code (accessing name_a and
>> name_b) is correct, and pins the correctness of the code you are
>> changing to it. If the second chunk is buggy, then you are actually
>> making the code worse.
>
> True. I think the original code structure design is name_a should
> always exist but name_b may not (the caller of run_diff_cmd() that
> eventually calls this call these "name" and "other", and the intent
> is renaming filepair is what needs "other").
>
>> I wonder if the implicit expectation of the function to take at least
>> one non-NULL name would be more obvious if the first few lines were
>> written as:
>>
>> if (DIFF_FILE_VALID(one)) {
>> if (!DIFF_FILE_VALID(two))
>> name_b = name_a;
>> } else if (DIFF_FILE_VALID(two))
>> name_a = name_b;
>> else
>> die("BUG: two invalid files to diff");
>>
>> That covers all of the cases explicitly, though it is IMHO uglier to
>> read (and there is still an implicit assumption that the name is
>> non-NULL if DIFF_FILE_VALID() is true).
>
> I think that is an overall improvement, especially if we also update
> the checks of {one,two}->mode made for the block that deals with
> submodules to use DIFF_FILE_VALID().
>
> Thanks.
>
So, do I understand your reasoning, when proposing this patch?
(This may break whitespaces as it's copied into my MUA, will resend with
git send-mail if you think this is the right thing.)
This patch just covers your discussion and not the previous patches.
Stefan
--8<--
From 701bab4f15598ba230552af7f1d5719187f1b2e8 Mon Sep 17 00:00:00 2001
From: Stefan Beller <stefanbeller@xxxxxxxxxxxxxx>
Date: Mon, 12 Aug 2013 10:29:07 +0200
Subject: [PATCH] diff: Additional error checking for input parameters
This makes the diff function error out instead of segfaulting if the
parameters are bad.
Helped-by: Jeff King <peff@xxxxxxxx>
Helped-by: Junio C Hamano <gitster@xxxxxxxxx>
Signed-off-by: Stefan Beller <stefanbeller@xxxxxxxxxxxxxx>
---
diff.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/diff.c b/diff.c
index e53ddad..de21971 100644
--- a/diff.c
+++ b/diff.c
@@ -2254,8 +2254,11 @@ static void builtin_diff(const char *name_a,
(!two->mode || S_ISGITLINK(two->mode))) {
const char *del = diff_get_color_opt(o, DIFF_FILE_OLD);
const char *add = diff_get_color_opt(o, DIFF_FILE_NEW);
- show_submodule_summary(o->file, one ? one->path : two->path,
- line_prefix,
+ struct diff_filespec *spec = one && DIFF_FILE_VALID(one) ? one : two;
+ if (!spec && !DIFF_FILE_VALID(spec))
+ die("BUG: two invalid diff_filespec structs in diff");
+
+ show_submodule_summary(o->file, spec->path, line_prefix,
one->sha1, two->sha1, two->dirty_submodule,
meta, del, add, reset);
return;
@@ -2276,8 +2279,13 @@ static void builtin_diff(const char *name_a,
}
/* Never use a non-valid filename anywhere if at all possible */
- name_a = DIFF_FILE_VALID(one) ? name_a : name_b;
- name_b = DIFF_FILE_VALID(two) ? name_b : name_a;
+ if (DIFF_FILE_VALID(one)) {
+ if (!DIFF_FILE_VALID(two))
+ name_b = name_a;
+ } else if (DIFF_FILE_VALID(two))
+ name_a = name_b;
+ else
+ die("BUG: two invalid files to diff");
a_one = quote_two(a_prefix, name_a + (*name_a == '/'));
b_two = quote_two(b_prefix, name_b + (*name_b == '/'));
--
1.8.4.rc2
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