On the Effectiveness of nonnull - revision history

Dank at 00:17, 13 March 2022

2022-03-13T00:17:56Z

← Older revision		Revision as of 00:17, 13 March 2022
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	ps i ended up getting rid of the copy when i fixed this, too. w00t! =]		ps i ended up getting rid of the copy when i fixed this, too. w00t! =]

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Dank at 00:49, 6 November 2021

2021-11-06T00:49:53Z

← Older revision		Revision as of 00:49, 6 November 2021
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	I add [https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html annotations] to my [[C]] programs pretty religiously, making most frequent use of:		I add [https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html annotations] to my [[C]] programs pretty religiously, making most frequent use of:

	* <tt>const</tt> and <tt>pure</tt> -- facilitate ~~subexpression~~ hoisting and memoization		* <tt>const</tt> and <tt>pure</tt> -- facilitate hoisting and memoization
	* <tt>malloc</tt> -- helps aliasing analysis and warning generation		* <tt>malloc</tt> -- helps aliasing analysis and warning generation
	* <tt>warn_unused_result</tt> -- warning generation		* <tt>warn_unused_result</tt> -- warning generation

Dank at 13:03, 5 November 2021

2021-11-05T13:03:49Z

← Older revision		Revision as of 13:03, 5 November 2021
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	and thus the inevitable "what? oh fuck what is this. no i just assigned to <tt>buf</tt>, you dumbass compiler, it could be <tt>NULL</tt> now, computer piece of shit, oh wait no fuck me in the ass, i assigned to <tt>*buf</tt> and checked <tt>buf</tt> like a witless simpleton asshole, fuck me in the ass twice, awww fuck piece of shit brain, thank you compiler you're a good compiler here's some more page cache, awww look at you chomping those pages you're my only friend, compiler."		and thus the inevitable "what? oh fuck what is this. no i just assigned to <tt>buf</tt>, you dumbass compiler, it could be <tt>NULL</tt> now, computer piece of shit, oh wait no fuck me in the ass, i assigned to <tt>*buf</tt> and checked <tt>buf</tt> like a witless simpleton asshole, fuck me in the ass twice, awww fuck piece of shit brain, thank you compiler you're a good compiler here's some more page cache, awww look at you chomping those pages you're my only friend, compiler."

			ps i ended up getting rid of the copy when i fixed this, too. w00t! =]

	'''next: "[[Four_questions_for_a_Wednesday\|four questions for a wednesday]]" 2021-10-13'''		'''next: "[[Four_questions_for_a_Wednesday\|four questions for a wednesday]]" 2021-10-13'''

	[[Category:Blog]]		[[Category:Blog]]

Dank at 07:10, 5 November 2021

2021-11-05T07:10:04Z

← Older revision		Revision as of 07:10, 5 November 2021
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	* <tt>sentinel</tt> in the unfortunate situations where it's applicable (did you really need varargs there? that's not how we raised you, son)		* <tt>sentinel</tt> in the unfortunate situations where it's applicable (did you really need varargs there? that's not how we raised you, son)

	and of course the ubiquitous <~~code~~>visibility("default")</~~code~~> (roughly) ala Microsoft's <tt>__declspec(dllexport)</tt>, which you ought be diligently employing on your shared libraries as [https://www.akkadia.org/drepper/dsohowto.pdf mr. drepper] taught you.		and of course the ubiquitous <tt>visibility("default")</tt> (roughly) ala Microsoft's <tt>__declspec(dllexport)</tt>, which you ought be diligently employing on your shared libraries as [https://www.akkadia.org/drepper/dsohowto.pdf mr. drepper] taught you.

	<tt>access</tt> lets you get fine-grained, Ada-like controls on your variable access types, but if i were writing Ada i'd be fucking with <tt>gnat</tt> and working for Northrop Grumman and questioning my life choices.		<tt>access</tt> lets you get fine-grained, Ada-like controls on your variable access types, but if i were writing Ada i'd be fucking with <tt>gnat</tt> and working for Northrop Grumman and questioning my life choices.

Dank at 07:05, 5 November 2021

2021-11-05T07:05:13Z

← Older revision		Revision as of 07:05, 5 November 2021
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	'''[[Dankblog\|dankblog!]] 2021-11-05, 0236 EDT, at [[Viewpoint\|the danktower]]'''		'''[[Dankblog\|dankblog!]] 2021-11-05, 0236 EDT, at [[Viewpoint\|the danktower]]'''

	I add ~~<code>nonnull</code>~~ [https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html annotations] to my [[C]] programs pretty religiously, making most frequent use of:		I add [https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html annotations] to my [[C]] programs pretty religiously, making most frequent use of:

	* <tt>const</tt> and <tt>pure</tt> -- facilitate subexpression hoisting and memoization		* <tt>const</tt> and <tt>pure</tt> -- facilitate subexpression hoisting and memoization
Line 17:		Line 17:
	<tt>access</tt> lets you get fine-grained, Ada-like controls on your variable access types, but if i were writing Ada i'd be fucking with <tt>gnat</tt> and working for Northrop Grumman and questioning my life choices.		<tt>access</tt> lets you get fine-grained, Ada-like controls on your variable access types, but if i were writing Ada i'd be fucking with <tt>gnat</tt> and working for Northrop Grumman and questioning my life choices.

	~~anyway~~, <tt>nonnull</tt> is all over the place, but it's usually added merely to satisfy the spergy part of my brain that also forces me to compulsively run <tt>ls</tt> every time i switch between terminals just to, like, ensure nothing shifted around. a pleasant surprise today when it caught a bug in my existing code:		finally, <tt>nonnull</tt> is all over the place, but it's usually added merely to satisfy the spergy part of my brain that also forces me to compulsively run <tt>ls</tt> every time i switch between terminals just to, like, ensure nothing shifted around. a pleasant surprise today when it caught a bug in my existing code:

	<syntaxhighlight lang="c">		<syntaxhighlight lang="c">

Dank at 07:04, 5 November 2021

2021-11-05T07:04:46Z

← Older revision		Revision as of 07:04, 5 November 2021
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	</syntaxhighlight>		</syntaxhighlight>

	OH SHIT, THERE GOES THE PLANET. that error check is completely pointless; indeed, the compiler might well elide it entirely (if <tt>buf</tt> is <tt>NULL</tt>, dereferencing it in the <tt>memdup</tt> line is undefined behavior, and the compiler can do whatever it wants. if it is not <tt>NULL</tt>, the check is pointless. thus work the mysterious minds of the ~~compiler people~~). a static analyzer arguably ought have picked up on this (and i run several analyzers regularly), but there's good reasons why not, also.		OH SHIT, THERE GOES THE PLANET. that error check is completely pointless; indeed, the compiler might well elide it entirely (if <tt>buf</tt> is <tt>NULL</tt>, dereferencing it in the <tt>memdup</tt> line is undefined behavior, and the compiler can do whatever it wants. if it is not <tt>NULL</tt>, the check is pointless. thus work the mysterious minds of the Compiler People). a static analyzer arguably ought have picked up on this (and i run several analyzers regularly), but there's good reasons why not, also.

	either way, adding <tt>nonnull(2)</tt> immediately generated the warning:		either way, adding <tt>nonnull(2)</tt> immediately generated the warning:

Dank: Created page with "'''dankblog! 2021-11-05, 0236 EDT, at the danktower''' I add `nonnull` [https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html anno..."

2021-11-05T07:03:15Z

Created page with "'''dankblog! 2021-11-05, 0236 EDT, at the danktower''' I add <code>nonnull</code> [https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html anno..."

New page

'''[[Dankblog|dankblog!]] 2021-11-05, 0236 EDT, at [[Viewpoint|the danktower]]'''

I add <code>nonnull</code> [https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html annotations] to my [[C]] programs pretty religiously, making most frequent use of:

* <tt>const</tt> and <tt>pure</tt> -- facilitate subexpression hoisting and memoization
* <tt>malloc</tt> -- helps aliasing analysis and warning generation
* <tt>warn_unused_result</tt> -- warning generation
* <tt>nonstring</tt> -- warning generation
* <tt>uninitialized</tt> in conjunction with <tt>-ftrivial-auto-var-init</tt>
* <tt>format</tt> -- warning generation for <tt>printf</tt>-style functions in conjunction with <tt>-Wformat</tt>, which ought probably be mandatory
* <tt>nothrow</tt> -- improves C++ code generation when exceptions are enabled. ought be on every C function you declare that doesn't call C++ (beware user-provided function pointers!)
* <tt>returns_nonnull</tt> -- improves code generation and static analysis
* <tt>sentinel</tt> in the unfortunate situations where it's applicable (did you really need varargs there? that's not how we raised you, son)

and of course the ubiquitous <code>visibility("default")</code> (roughly) ala Microsoft's <tt>__declspec(dllexport)</tt>, which you ought be diligently employing on your shared libraries as [https://www.akkadia.org/drepper/dsohowto.pdf mr. drepper] taught you.

<tt>access</tt> lets you get fine-grained, Ada-like controls on your variable access types, but if i were writing Ada i'd be fucking with <tt>gnat</tt> and working for Northrop Grumman and questioning my life choices.

anyway, <tt>nonnull</tt> is all over the place, but it's usually added merely to satisfy the spergy part of my brain that also forces me to compulsively run <tt>ls</tt> every time i switch between terminals just to, like, ensure nothing shifted around. a pleasant surprise today when it caught a bug in my existing code:

<syntaxhighlight lang="c">
// for now, we just run the top half of notcurses_render(), and copy out the
// memstream from within rstate. we want to allocate our own here, and return
// it, to avoid the copy, but we need feed the params through to do so FIXME.
int ncpile_render_to_buffer(ncplane* p, char** buf, size_t* buflen){
if(ncpile_render(p)){
return -1;
}
notcurses* nc = ncplane_notcurses(p);
unsigned useasu = false; // no SUM with file
fbuf_reset(&nc->rstate.f);
int bytes = notcurses_rasterize_inner(nc, ncplane_pile(p), &nc->rstate.f, &useasu);
pthread_mutex_lock(&nc->stats.lock);
update_render_bytes(&nc->stats.s, bytes);
pthread_mutex_unlock(&nc->stats.lock);
if(bytes < 0){
return -1;
}
*buf = memdup(nc->rstate.f.buf, nc->rstate.f.used);
if(buf == NULL){
return -1;
}
*buflen = nc->rstate.f.used;
return 0;
}
</syntaxhighlight>

ignore the nonsensical mouthfoam in the opening comment. do you see the bug? it ought require no knowledge of the content beyond standard ANSI C to do so.

...see it yet?

<syntaxhighlight lang="c">
*buf = memdup(nc->rstate.f.buf, nc->rstate.f.used);
if(buf == NULL){
return -1;
}
</syntaxhighlight>

OH SHIT, THERE GOES THE PLANET. that error check is completely pointless; indeed, the compiler might well elide it entirely (if <tt>buf</tt> is <tt>NULL</tt>, dereferencing it in the <tt>memdup</tt> line is undefined behavior, and the compiler can do whatever it wants. if it is not <tt>NULL</tt>, the check is pointless. thus work the mysterious minds of the compiler people). a static analyzer arguably ought have picked up on this (and i run several analyzers regularly), but there's good reasons why not, also.

either way, adding <tt>nonnull(2)</tt> immediately generated the warning:

<pre>
/home/dank/src/dankamongmen/notcurses/src/lib/render.c: In function ‘ncpile_render_to_buffer’:
/home/dank/src/dankamongmen/notcurses/src/lib/render.c:1561:5: warning: ‘nonnull’ argument ‘buf’ compared to NULL [-Wnonnull-compare]
1561 | if(buf == NULL){
| ^
</pre>

and thus the inevitable "what? oh fuck what is this. no i just assigned to <tt>buf</tt>, you dumbass compiler, it could be <tt>NULL</tt> now, computer piece of shit, oh wait no fuck me in the ass, i assigned to <tt>*buf</tt> and checked <tt>buf</tt> like a witless simpleton asshole, fuck me in the ass twice, awww fuck piece of shit brain, thank you compiler you're a good compiler here's some more page cache, awww look at you chomping those pages you're my only friend, compiler."

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