From: Jeff King <peff@peff.net>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Git List" <git@vger.kernel.org>, "René Scharfe" <l.s.r@web.de>,
"Andreas Schwab" <schwab@linux-m68k.org>,
"Johannes Sixt" <j6t@kdbg.org>
Subject: Re: [PATCH] strbuf: use designated initializers in STRBUF_INIT
Date: Fri, 14 Jul 2017 13:36:58 -0400 [thread overview]
Message-ID: <20170714173658.2q24oxhatwh5qrqk@sigill.intra.peff.net> (raw)
In-Reply-To: <xmqqlgnrq9qi.fsf@gitster.mtv.corp.google.com>
On Fri, Jul 14, 2017 at 09:11:33AM -0700, Junio C Hamano wrote:
> As to other things that we currently not allow in our codebase that
> newer compilers can grok, here is what *I* think. It is *not* meant
> to be an exhaustive "what's new in C99 that is not in C89? what is
> the final verdict on each of them?":
>
> - There were occasional cases where we wished if variable-length
> arrays, flexible array members and variadic macros were available
> in our codebase during the course of this project. We would
> probably want to add a similar test baloon patch for each of
> them to this series that is currently two-patch long.
I think variable-length arrays are potentially dangerous. They're
allocated on the stack, which creates two issues:
1. You can run out of stack space and segfault, whereas the same
operation with a heap buffer would be fine. You can say "but this
VLA will only be used for small things". But then, you can just as
easily declare a small stack buffer.
2. My understanding of the recent "Stack Clash" class of
vulnerabilities[1] is that VLAs make the attacker's job much easier
(since they can often just send a large input to get you to
allocate a large stack).
I think variadic macros are a good candidate, though. There have been a
number of times where we've had to sacrifice functionality or
readability in our helper functions. E.g., the case mentioned in
368953912 (add helpers for allocating flex-array structs, 2016-02-22).
The weather-balloon patch for that should be easy, too: just drop the
fallback macros from BUG() or the trace code.
[1] https://www.qualys.com/2017/06/19/stack-clash/stack-clash.txt
> - I prefer to keep decl-after-statement out of our codebase. I
> view it as a big plus in code-readability to be able to see a
> complete list of variables that will be used in a block upfront
> before starting to read the code that uses them.
>
> - Corollary to the above, I do not mind to have a variable
> declaration in the initialization clause of a for() statement
> (e.g. "for (int i = 0; i < 4; i++) { ... }"), as the scoping rule
> is very sensible. Some of our "for()" statements use the value
> of the variable after iteration, for which this new construct
> cannot be used, though.
I agree with both of those points. I think the decl-in-for is nice
exactly because it highlights those cases where the iteration variable's
value is relevant after the loop ends.
> - This may be showing I am not just old fashioned but also am
> ignorant, but I do not see much point in using the following in
> our codebase (iow, I am not aware of places in the existing code
> that they can be improved by employing these features):
>
> . // comments
> . restricted pointers
> . static and type qualifiers in parameter array declarators
Agreed, though I think the comment thing is a personal taste issue (just
not my taste).
> +static int clean_use_color = -1;
> +static char clean_colors[][COLOR_MAXLEN] = {
> + [CLEAN_COLOR_RESET] = GIT_COLOR_RESET,
> + [CLEAN_COLOR_PLAIN] = GIT_COLOR_NORMAL,
> + [CLEAN_COLOR_PROMPT] = GIT_COLOR_BOLD_BLUE,
> + [CLEAN_COLOR_HEADER] = GIT_COLOR_BOLD,
> + [CLEAN_COLOR_HELP] = GIT_COLOR_BOLD_RED,
> + [CLEAN_COLOR_ERROR] = GIT_COLOR_BOLD_RED,
> +};
I think this is much nicer to read. I assume if we have a "hole" in our
numbering that the hole is initialized in the usual static way (a
COLOR_MAXLEN array full of NULs in this case, I guess)?
-Peff
next prev parent reply other threads:[~2017-07-14 17:37 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-10 7:03 [PATCH] strbuf: use designated initializers in STRBUF_INIT Jeff King
2017-07-10 14:57 ` Ben Peart
2017-07-10 16:04 ` Jeff King
2017-07-10 17:57 ` Ben Peart
2017-07-11 5:01 ` Mike Hommey
2017-07-11 15:31 ` Junio C Hamano
2017-07-12 19:12 ` Ævar Arnfjörð Bjarmason
2017-07-12 21:08 ` Junio C Hamano
2017-07-13 22:24 ` Johannes Sixt
2017-07-10 16:44 ` Junio C Hamano
2017-07-10 17:33 ` Stefan Beller
2017-07-10 21:46 ` Junio C Hamano
2017-07-10 17:10 ` Andreas Schwab
2017-07-10 19:57 ` Johannes Sixt
2017-07-10 20:38 ` Junio C Hamano
2017-07-10 21:11 ` Johannes Sixt
2017-07-10 21:38 ` Junio C Hamano
2017-07-14 16:11 ` Junio C Hamano
2017-07-14 17:13 ` Stefan Beller
2017-07-14 17:36 ` Jeff King [this message]
2017-07-14 18:48 ` Junio C Hamano
2017-07-14 19:16 ` Junio C Hamano
2017-07-19 18:19 ` [PATCH] objects: scope count variable to loop Stefan Beller
2017-07-19 18:23 ` Brandon Williams
2017-07-24 17:08 ` Jeff King
2017-07-24 17:12 ` Stefan Beller
2017-07-24 18:05 ` Jeff King
2017-07-14 19:28 ` [PATCH] strbuf: use designated initializers in STRBUF_INIT Ævar Arnfjörð Bjarmason
2017-07-14 22:26 ` Junio C Hamano
2017-07-14 22:43 ` Mike Hommey
2017-07-15 11:08 ` Jeff King
2017-07-11 4:38 ` Jeff King
2017-07-11 0:05 ` brian m. carlson
2017-07-11 0:07 ` Stefan Beller
2017-07-11 0:10 ` brian m. carlson
2017-07-11 5:24 ` Johannes Sixt
2017-07-12 1:26 ` brian m. carlson
2017-07-12 18:25 ` Johannes Sixt
2017-07-10 22:41 ` Brandon Williams
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