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From: Junio C Hamano <gitster@pobox.com>
To: "Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>
Cc: git@vger.kernel.org, vdye@github.com,
	"SZEDER Gábor" <szeder.dev@gmail.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Derrick Stolee" <derrickstolee@github.com>
Subject: Re: [PATCH v4 4/4] string-list: document iterator behavior on NULL input
Date: Tue, 27 Sep 2022 09:39:56 -0700	[thread overview]
Message-ID: <xmqqmtak7ov7.fsf@gitster.g> (raw)
In-Reply-To: <73a262cdca46a45aeeda6f47ea3357aaeb937e7b.1664287021.git.gitgitgadget@gmail.com> (Derrick Stolee via GitGitGadget's message of "Tue, 27 Sep 2022 13:57:01 +0000")

"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com> writes:

> From: Derrick Stolee <derrickstolee@github.com>
>
> The for_each_string_list_item() macro takes a string_list and
> automatically constructs a for loop to iterate over its contents. This
> macro will segfault if the list is non-NULL.
>
> We cannot change the macro to be careful around NULL values because
> there are many callers that use the address of a local variable, which
> will never be NULL and will cause compile errors with -Werror=address.
>
> For now, leave a documentation comment to try to avoid mistakes in the
> future where a caller does not check for a NULL list.
>
> Signed-off-by: Derrick Stolee <derrickstolee@github.com>
> ---
>  string-list.h | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)

For exactly the -Werror=address reason, any other way that checks
list for NULL-ness cannot be done here (other than with Peff's
inline helper that returns the first item or NULL), which is a bit
of shame but this is totally outside the topic, and an additional
comment is a good thing to have here.

Thanks.  All four patches look reasonable.  Will queue (but after I
make sure I can tag and push out -rc2 today).


> diff --git a/string-list.h b/string-list.h
> index d5a744e1438..c7b0d5d0008 100644
> --- a/string-list.h
> +++ b/string-list.h
> @@ -141,7 +141,12 @@ void string_list_clear_func(struct string_list *list, string_list_clear_func_t c
>  int for_each_string_list(struct string_list *list,
>  			 string_list_each_func_t func, void *cb_data);
>  
> -/** Iterate over each item, as a macro. */
> +/**
> + * Iterate over each item, as a macro.
> + *
> + * Be sure that 'list' is non-NULL. The macro cannot perform NULL
> + * checks due to -Werror=address errors.
> + */
>  #define for_each_string_list_item(item,list)            \
>  	for (item = (list)->items;                      \
>  	     item && item < (list)->items + (list)->nr; \

  reply	other threads:[~2022-09-27 16:40 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-20  1:02 [PATCH] maintenance: make unregister idempotent Derrick Stolee via GitGitGadget
2022-09-21 17:19 ` Junio C Hamano
2022-09-22 12:37   ` Derrick Stolee
2022-09-22 19:31     ` Junio C Hamano
2022-09-22 19:46       ` Derrick Stolee
2022-09-22 20:44         ` Junio C Hamano
2022-09-22 13:37 ` [PATCH v2 0/2] scalar: " Derrick Stolee via GitGitGadget
2022-09-22 13:37   ` [PATCH v2 1/2] maintenance: add 'unregister --force' Derrick Stolee via GitGitGadget
2022-09-23 13:08     ` SZEDER Gábor
2022-09-26 13:32       ` Derrick Stolee
2022-09-26 15:39         ` Ævar Arnfjörð Bjarmason
2022-09-26 17:25           ` Derrick Stolee
2022-09-26 19:17             ` Junio C Hamano
2022-09-22 13:37   ` [PATCH v2 2/2] scalar: make 'unregister' idempotent Derrick Stolee via GitGitGadget
2022-09-26 18:48   ` [PATCH v3 0/3] scalar: make unregister idempotent Derrick Stolee via GitGitGadget
2022-09-26 18:48     ` [PATCH v3 1/3] maintenance: add 'unregister --force' Derrick Stolee via GitGitGadget
2022-09-26 19:23       ` Junio C Hamano
2022-09-26 20:49         ` Derrick Stolee
2022-09-26 21:55       ` Junio C Hamano
2022-09-27 11:38         ` Derrick Stolee
2022-09-27 11:54           ` Derrick Stolee
2022-09-27 13:36             ` Ævar Arnfjörð Bjarmason
2022-09-27 13:55               ` Derrick Stolee
2022-09-26 18:48     ` [PATCH v3 2/3] scalar: make 'unregister' idempotent Derrick Stolee via GitGitGadget
2022-09-26 18:48     ` [PATCH v3 3/3] gc: replace config subprocesses with API calls Derrick Stolee via GitGitGadget
2022-09-26 19:27       ` Junio C Hamano
2022-09-27 13:56     ` [PATCH v4 0/4] scalar: make unregister idempotent Derrick Stolee via GitGitGadget
2022-09-27 13:56       ` [PATCH v4 1/4] maintenance: add 'unregister --force' Derrick Stolee via GitGitGadget
2022-09-27 13:56       ` [PATCH v4 2/4] scalar: make 'unregister' idempotent Derrick Stolee via GitGitGadget
2022-09-27 13:57       ` [PATCH v4 3/4] gc: replace config subprocesses with API calls Derrick Stolee via GitGitGadget
2022-09-27 13:57       ` [PATCH v4 4/4] string-list: document iterator behavior on NULL input Derrick Stolee via GitGitGadget
2022-09-27 16:39         ` Junio C Hamano [this message]
2022-09-27 16:31       ` [PATCH v4 0/4] scalar: make unregister idempotent Junio C Hamano
2022-09-27 16:54         ` Derrick Stolee

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