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From: Matheus Tavares <matheus.bernardino@usp.br>
To: johannes.schindelin@gmx.de
Cc: christian.couder@gmail.com, frekui@gmail.com,
	git@vger.kernel.org, j6t@kdbg.org, jonathantanmy@google.com,
	matheus.bernardino@usp.br, peff@peff.net,
	sandals@crustytoothpaste.net
Subject: Re: [PATCH v2 2/2] hex: make hash_to_hex_algop() and friends thread-safe
Date: Sat, 18 Jul 2020 00:52:01 -0300	[thread overview]
Message-ID: <20200718035201.42233-1-matheus.bernardino@usp.br> (raw)
In-Reply-To: <nycvar.QRO.7.76.6.2007161214270.54@tvgsbejvaqbjf.bet>

On Thu, Jul 16, 2020 at 9:56 AM Johannes Schindelin <Johannes.Schindelin@gmx.de> wrote:
>
> Now, I am _far_ from knowing what I'm doing with Coccinelle, but I think
> this here semantic patch should get you going:
>
> -- snipsnap --
> @@
> expression E;
> @@
>   {
> ++   char hex[GIT_MAX_HEXSZ + 1];
>      ...
> -    oid_to_hex(E)
> +    oid_to_hex_r(hex, E)
>      ...
>   }
>
> @@
> expression E1, E2;
> @@
>   {
> ++   char hex1[GIT_MAX_HEXSZ + 1], hex2[GIT_MAX_HEXSZ + 1];
>      ...
> -    oid_to_hex(E1)
> +    oid_to_hex_r(hex1, E1)
>      ...
> -    oid_to_hex(E2)
> +    oid_to_hex_r(hex2, E2)
>      ...
>   }

Thanks for this nice example! This already worked very well in some of
my tests :)

However, with my _very_ limited notion of Coccinelle, I didn't
understand why some code snippets didn't match the above rules. For
example, the structure below:

func(...)
{
	if (cond)
		func2("%s", oid_to_hex(a));
}

I thought it could be because the `if` statement is missing the curly
brackets (and it does work if I add the brackets), but to my surprise,
adding another oid_to_hex() call in an `else` case also made the code
match the rule:

func(...)
{
	if (cond)
		func2("%s", oid_to_hex(a));
	else
		func2("%s", oid_to_hex(a));
}

The following snippet also correctly matches, but spatch introduces only
one `hex` variable:

	if (cond)
		func2("%s, %s", oid_to_hex(a), oid_to_hex(b));
	else
		func2("%s", oid_to_hex(a));

We will probably want our semantic rules to handle an arbitrary number
of `oid_to_hex()` calls in each function, but in scenarios like the
above one, we only really need 2 hex buffers despite having 3 calls...
That might be a little tricky, I guess.

Another thing that might be tricky in this conversion is checking for
name conflicts with the added `hex` variable (but maybe Coccinelle
already has a facilitator mechanism for such cases? IDK).

  parent reply	other threads:[~2020-07-18  3:52 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-24 22:29 [RFC] Thread safety in some low-level functions Matheus Tavares Bernardino
2020-06-24 22:52 ` Matheus Tavares Bernardino
2020-06-25  1:38   ` brian m. carlson
2020-06-25 20:32     ` [PATCH 0/2] Make oid_to_hex() thread-safe Matheus Tavares
2020-06-25 20:32       ` [PATCH 1/2] compat/win32/pthread: add pthread_once() Matheus Tavares
2020-06-26  5:45         ` Christian Couder
2020-06-26 14:13           ` Matheus Tavares Bernardino
2020-06-25 20:32       ` [PATCH 2/2] hex: make hash_to_hex_algop() and friends thread-safe Matheus Tavares
2020-06-25 23:07         ` brian m. carlson
2020-06-25 23:54           ` Matheus Tavares Bernardino
2020-06-26  0:00             ` Matheus Tavares Bernardino
2020-06-26  6:02         ` Christian Couder
2020-06-26  8:22       ` [PATCH 0/2] Make oid_to_hex() thread-safe Christian Couder
2020-06-26 16:22         ` Matheus Tavares Bernardino
2020-06-26 21:54       ` [PATCH v2 " Matheus Tavares
2020-06-26 21:54         ` [PATCH v2 1/2] compat/win32/pthread: add pthread_once() Matheus Tavares
2020-06-26 21:54         ` [PATCH v2 2/2] hex: make hash_to_hex_algop() and friends thread-safe Matheus Tavares
2020-06-29 15:11           ` Johannes Schindelin
2020-06-30 20:37             ` Matheus Tavares Bernardino
2020-07-01 11:32               ` Johannes Schindelin
2020-07-16 11:29           ` Johannes Schindelin
2020-07-18  3:09             ` Matheus Tavares Bernardino
2020-08-10 14:15               ` Johannes Schindelin
2020-07-18  3:52             ` Matheus Tavares [this message]
2020-07-26 17:41               ` René Scharfe

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