Hey everybody,
in today's leadership meeting, the question was brought up if we want to normalize the coding style in coreboot to _always_ use braces in if, else and for statements, even if it's just one statement they're wrapping.
The arguments made in favor were:
1. it's more consistent 2. it's safer: you won't accidentally add a statement that is outside the context it's supposed to run in (or even move a statement out into the parent context by inserting another statement)
So instead of:
if (foo) bar(); else { baz(); quux(); }
we'd do:
if (foo) { bar(); } else { baz(); quux(); }
The attendees were generally in favor, but wanted to ask the wider community. The idea of putting it up for a vote was brought up, but we decided to discuss it first (and vote if there's disagreement, after the arguments were exchanged. makes for clearer arguments for all positions on the ballot, too)
Patrick
On Wed, Jun 19, 2019 at 01:39:50PM -0400, Patrick Georgi via coreboot wrote:
Hey everybody,
in today's leadership meeting, the question was brought up if we want to normalize the coding style in coreboot to _always_ use braces in if, else and for statements, even if it's just one statement they're wrapping.
The arguments made in favor were:
- it's more consistent
- it's safer: you won't accidentally add a statement that is outside the context it's supposed to run in (or even move a statement out into the parent context by inserting another statement)
So instead of:
if (foo) bar(); else { baz(); quux(); }
we'd do:
if (foo) { bar(); } else { baz(); quux(); }
Quick sidenote: Under the old rules[1], inherited from the Linux kernel coding style[2], the above example would look the same:
| [...] | This does not apply if only one branch of a conditional statement is a | single statement; in the latter case use braces in both branches: | | if (condition) { | do_this(); | do_that(); | } else { | otherwise(); | }
... so a better example would be one where technically no parentheses are required at all:
if (foo) bar(); else baz();
becomes:
if (foo) { bar(); } else { baz(); }
greetings, Jonathan Neuschäfer
[1]: https://doc.coreboot.org/coding_style.html#placing-braces-and-spaces [2]: https://www.kernel.org/doc/html/latest/process/coding-style.html?highlight=c...
Given the number of serious problems that lack of braces causes, I like this proposal. It's indicative that both Rust and Go require the {}, for reasons of safety.
On Wed, Jun 19, 2019 at 11:27 AM Jonathan Neuschäfer j.neuschaefer@gmx.net wrote:
On Wed, Jun 19, 2019 at 01:39:50PM -0400, Patrick Georgi via coreboot wrote:
Hey everybody,
in today's leadership meeting, the question was brought up if we want to normalize the coding style in coreboot to _always_ use braces in if, else and for statements, even if it's just one statement they're wrapping.
The arguments made in favor were:
- it's more consistent
- it's safer: you won't accidentally add a statement that is outside the context it's supposed to run in (or even move a statement out into the parent context by inserting another statement)
So instead of:
if (foo) bar(); else { baz(); quux(); }
we'd do:
if (foo) { bar(); } else { baz(); quux(); }
Quick sidenote: Under the old rules[1], inherited from the Linux kernel coding style[2], the above example would look the same:
| [...] | This does not apply if only one branch of a conditional statement is a | single statement; in the latter case use braces in both branches: | | if (condition) { | do_this(); | do_that(); | } else { | otherwise(); | }
... so a better example would be one where technically no parentheses are required at all:
if (foo) bar(); else baz();becomes:
if (foo) { bar(); } else { baz(); }greetings, Jonathan Neuschäfer
coreboot mailing list -- coreboot@coreboot.org To unsubscribe send an email to coreboot-leave@coreboot.org
On Wed, Jun 19, 2019 at 08:38:14PM -0700, ron minnich wrote:
Given the number of serious problems that lack of braces causes, I like this proposal. It's indicative that both Rust and Go require the {}, for reasons of safety.
There was a famous vulnerability in Apple's SSL code several years ago because of lack of braces. clang-format can also reformat old code to have mandatory braces if I'm not mistaken.
Jacob Garber
On 20.06.19 06:01, Jacob Garber wrote:
On Wed, Jun 19, 2019 at 08:38:14PM -0700, ron minnich wrote:
Given the number of serious problems that lack of braces causes, I like this proposal. It's indicative that both Rust and Go require the {}, for reasons of safety.
There was a famous vulnerability in Apple's SSL code several years ago because of lack of braces. clang-format can also reformat old code to have mandatory braces if I'm not mistaken.
What will clang-format do if it encounters?
if (foo) bar(); baz();
a) if (foo) { bar(); } baz();
or b) if (foo) { bar(); baz(); }
Will it spit out a warning? If not, this shows how dangerous automatic formatting can be. Because after the formatter run, it's much less ob- vious for the reviewer that something is wrong.
Nico
clang-format is not a textual preprocessor. It is basically the ast builder of followed by output.
So in your case, I just tried it main() {
if (foo) bar(); baz(); }
and got the right thing, i.e. braces around bar but not baz.
The history of reviewers looking at code is they miss this kind of error. Constantly. I'm in favor of as much automation as we can get.
ron
On Thu, Jun 20, 2019 at 5:25 AM Nico Huber nico.h@gmx.de wrote:
On 20.06.19 06:01, Jacob Garber wrote:
On Wed, Jun 19, 2019 at 08:38:14PM -0700, ron minnich wrote:
Given the number of serious problems that lack of braces causes, I like this proposal. It's indicative that both Rust and Go require the {}, for reasons of safety.
There was a famous vulnerability in Apple's SSL code several years ago because of lack of braces. clang-format can also reformat old code to have mandatory braces if I'm not mistaken.
What will clang-format do if it encounters?
if (foo) bar(); baz();a) if (foo) { bar(); } baz();
or b) if (foo) { bar(); baz(); }
Will it spit out a warning? If not, this shows how dangerous automatic formatting can be. Because after the formatter run, it's much less ob- vious for the reviewer that something is wrong.
Nico
What Ron said, plus if I recall Coverity has a lint for misleading indentation, so I don't think there are any current instances of this in the code base. In fact, GCC even has -Wmisleading-indentation that was added to -Wall in GCC 6, so we should currently be ok. That being said, these warnings are only heuristics (there's no precise definition of what "misleading" is supposed to be), so I don't think they should be relied upon over using braces, which avoids this problem entirely.
Jacob
On Thu, Jun 20, 2019 at 08:26:49AM -0700, ron minnich wrote:
clang-format is not a textual preprocessor. It is basically the ast builder of followed by output.
So in your case, I just tried it main() {
if (foo) bar(); baz(); }
and got the right thing, i.e. braces around bar but not baz.
The history of reviewers looking at code is they miss this kind of error. Constantly. I'm in favor of as much automation as we can get.
ron
On Thu, Jun 20, 2019 at 5:25 AM Nico Huber nico.h@gmx.de wrote:
On 20.06.19 06:01, Jacob Garber wrote:
On Wed, Jun 19, 2019 at 08:38:14PM -0700, ron minnich wrote:
Given the number of serious problems that lack of braces causes, I like this proposal. It's indicative that both Rust and Go require the {}, for reasons of safety.
There was a famous vulnerability in Apple's SSL code several years ago because of lack of braces. clang-format can also reformat old code to have mandatory braces if I'm not mistaken.
What will clang-format do if it encounters?
if (foo) bar(); baz();a) if (foo) { bar(); } baz();
or b) if (foo) { bar(); baz(); }
Will it spit out a warning? If not, this shows how dangerous automatic formatting can be. Because after the formatter run, it's much less ob- vious for the reviewer that something is wrong.
Nico
On 20.06.19 18:12, Jacob Garber wrote:
What Ron said, plus if I recall Coverity has a lint for misleading indentation, so I don't think there are any current instances of this in the code base. In fact, GCC even has -Wmisleading-indentation that was added to -Wall in GCC 6, so we should currently be ok. That being said, these warnings are only heuristics (there's no precise definition of what "misleading" is supposed to be), so I don't think they should be relied upon over using braces, which avoids this problem entirely.
That's all true, but it forces an order of the tools you run. e.g. don't integrate clang-format into your editor because it might hide the problem before the compiler can warn you.
Nico
On 20.06.19 17:26, ron minnich wrote:
clang-format is not a textual preprocessor. It is basically the ast builder of followed by output.
So in your case, I just tried it main() {
if (foo) bar(); baz(); }
and got the right thing, i.e. braces around bar but not baz.
The history of reviewers looking at code is they miss this kind of error. Constantly. I'm in favor of as much automation as we can get.
Sorry, I guess I wasn't clear enough, we're talking past each other. What I meant is that if somebody writes
if (foo) bar(); baz();
they most probably forgot the _necessary_ braces and clang-format would hide this intention even from a human reviewer.
Nico
Am Do., 20. Juni 2019 um 21:47 Uhr schrieb Nico Huber nico.h@gmx.de:
That's all true, but it forces an order of the tools you run. e.g. don't integrate clang-format into your editor because it might hide the problem before the compiler can warn you.
So don't integrate clang-format into your editor unless you also add some C checker that knows about indentation (eg. a gcc/clang based LSP like https://clang.llvm.org/extra/clangd/) for live feedback.
Patrick
On Thu, Jun 20, 2019 at 1:12 PM Stefan Reinauer stefan.reinauer@coreboot.org wrote:
On 20 Jun 2019 08:26, ron minnich rminnich@gmail.com wrote:
clang-format is not a textual preprocessor. It is basically the ast builder of followed by output.
So in your case, I just tried it main() {
if (foo) bar(); baz(); }
and got the right thing, i.e. braces around bar but not baz.
The right thing (e.g. the obviously intended thing) would be too have braces around both.
clang-format in this case masks the problem and makes it harder to identify by expanding the syntax of the unwanted behavior to look intentional.
Nico and Stefan, you make a good point, but I would then argue for even better tools, like clang-tidy: /tmp/x.c:13:10: warning: statement should be inside braces [readability-braces-around-statements] if (foo) ^ {
In this case, there is a warning thrown, and the author has to clean it up.
I don't believe, based on a lot of the history of this sort of problem in C, that we should depend on human reviewers to catch mistakes like this. These tools exist because of a demonstrated need. I think coreboot could benefit from their proper application.
You've presented a good case, but what about something like this: if (foo) bar(); baz();
what's intended? There's an indent, but it's partial. I would not want to guess. But I agree with you that an invisible fixup would be inappropriate.
Doesn't -Wmisleading-indentation already catch all of this? That's enabled by default on the coreboot gcc. I don't think "it's just a heuristic" should be a concern unless anyone knows of a real example that is otherwise valid coreboot code style but not caught by this heuristic. (If we're worried about examples that are not valid code style, then changing the code style to make them even more forbidden doesn't help... so I think weird cases that mix tab and space indentation or the like should count in favor of this.)
If we're concerned that clang-format might cement errors automatically then that's a reason for not using clang-format that way, but I don't see how changing the coding style would solve it. clang-format's whole job is to take whatever input and transform it into the coding style, so the input is likely not style-compliant yet.
Forcing braces on single-line statements adds an extra line of whitespace where it would otherwise not necessarily belong, which hurts readability. How much of a function can fit on a single screen is a real readability concern, and I think this style change would harm it. That's the same reason we write
while {
instead of
while {
like some other projects. (Of course blank lines can also help readability, but only in the *right* places and not randomly injected by style rules.) It would also move us yet again further away from kernel style, causing more issues for people coming from other projects.
On Thu, Jun 20, 2019 at 2:54 PM ron minnich rminnich@gmail.com wrote:
On Thu, Jun 20, 2019 at 1:12 PM Stefan Reinauer stefan.reinauer@coreboot.org wrote:
On 20 Jun 2019 08:26, ron minnich rminnich@gmail.com wrote:
clang-format is not a textual preprocessor. It is basically the ast builder of followed by output.
So in your case, I just tried it main() {
if (foo) bar(); baz(); }
and got the right thing, i.e. braces around bar but not baz.
The right thing (e.g. the obviously intended thing) would be too have braces around both.
clang-format in this case masks the problem and makes it harder to identify by expanding the syntax of the unwanted behavior to look intentional.
Nico and Stefan, you make a good point, but I would then argue for even better tools, like clang-tidy: /tmp/x.c:13:10: warning: statement should be inside braces [readability-braces-around-statements] if (foo) ^ {
In this case, there is a warning thrown, and the author has to clean it up.
I don't believe, based on a lot of the history of this sort of problem in C, that we should depend on human reviewers to catch mistakes like this. These tools exist because of a demonstrated need. I think coreboot could benefit from their proper application.
You've presented a good case, but what about something like this: if (foo) bar(); baz();
what's intended? There's an indent, but it's partial. I would not want to guess. But I agree with you that an invisible fixup would be inappropriate. _______________________________________________ coreboot mailing list -- coreboot@coreboot.org To unsubscribe send an email to coreboot-leave@coreboot.org
If we're going to talk about wasted lines consider this: we mandate comments as follows: /* * something */
I just did a test and we have something like 40K lines of white space spent on that dangling */.
We've got something like 30K if not followed by {
So, were we to to get away from the comments with "wings" (as some kernel people once called them) we could save all those lines with just a /* or */ on them. This would more than make up for additional white lines added by a dangling {.
I note that the changing our comment style would have zero impact on code safety. The improvement of requiring a { on the ifs is known to have positive impact; it's why Rust and Go both require it to my understanding.
As for "the kernel" and its coding style, we are going to increasingly see people coming from worlds where "the kernel" and its coding style matter less and less. Maybe adherence to "the kernel" coding style mattered ten years ago; I don't think it is as important now. In my case, increasingly, "the kernel" coding style is looking a bit dated.
On Mon, Jun 24, 2019 at 8:14 PM Julius Werner jwerner@chromium.org wrote:
Doesn't -Wmisleading-indentation already catch all of this? That's enabled by default on the coreboot gcc. I don't think "it's just a heuristic" should be a concern unless anyone knows of a real example that is otherwise valid coreboot code style but not caught by this heuristic. (If we're worried about examples that are not valid code style, then changing the code style to make them even more forbidden doesn't help... so I think weird cases that mix tab and space indentation or the like should count in favor of this.)
If we're concerned that clang-format might cement errors automatically then that's a reason for not using clang-format that way, but I don't see how changing the coding style would solve it. clang-format's whole job is to take whatever input and transform it into the coding style, so the input is likely not style-compliant yet.
Forcing braces on single-line statements adds an extra line of whitespace where it would otherwise not necessarily belong, which hurts readability. How much of a function can fit on a single screen is a real readability concern, and I think this style change would harm it. That's the same reason we write
while {
instead of
while {
like some other projects. (Of course blank lines can also help readability, but only in the *right* places and not randomly injected by style rules.) It would also move us yet again further away from kernel style, causing more issues for people coming from other projects.
On Thu, Jun 20, 2019 at 2:54 PM ron minnich rminnich@gmail.com wrote:
On Thu, Jun 20, 2019 at 1:12 PM Stefan Reinauer stefan.reinauer@coreboot.org wrote:
On 20 Jun 2019 08:26, ron minnich rminnich@gmail.com wrote:
clang-format is not a textual preprocessor. It is basically the ast builder of followed by output.
So in your case, I just tried it main() {
if (foo) bar(); baz(); }
and got the right thing, i.e. braces around bar but not baz.
The right thing (e.g. the obviously intended thing) would be too have braces around both.
clang-format in this case masks the problem and makes it harder to identify by expanding the syntax of the unwanted behavior to look intentional.
Nico and Stefan, you make a good point, but I would then argue for even better tools, like clang-tidy: /tmp/x.c:13:10: warning: statement should be inside braces [readability-braces-around-statements] if (foo) ^ {
In this case, there is a warning thrown, and the author has to clean it up.
I don't believe, based on a lot of the history of this sort of problem in C, that we should depend on human reviewers to catch mistakes like this. These tools exist because of a demonstrated need. I think coreboot could benefit from their proper application.
You've presented a good case, but what about something like this: if (foo) bar(); baz();
what's intended? There's an indent, but it's partial. I would not want to guess. But I agree with you that an invisible fixup would be inappropriate. _______________________________________________ coreboot mailing list -- coreboot@coreboot.org To unsubscribe send an email to coreboot-leave@coreboot.org
we mandate comments as follows: /*
- something
*/
No we don't. We had a long discussion about multi-line comment styles some years back and I made the same argument there. ;) That's why our coding style now allows two versions so you can pick whatever suits the situation at hand better:
/* * long * form */
/* short form */
I note that the changing our comment style would have zero impact on code safety. The improvement of requiring a { on the ifs is known to have positive impact; it's why Rust and Go both require it to my understanding.
How is this actually "known"? Does that take the (relatively recent) -Wmisleading-indentation into account? I think after all these years where this has not (to my knowledge) caused any problems to coreboot, "fixing" it now that we even have a compiler check to catch it seems weird. It's complicating things for humans in favor of something that a machine can (and already does) solve just as well.
As for "the kernel" and its coding style, we are going to increasingly see people coming from worlds where "the kernel" and its coding style matter less and less. Maybe adherence to "the kernel" coding style mattered ten years ago; I don't think it is as important now. In my case, increasingly, "the kernel" coding style is looking a bit dated.
Are we? Why? I've helped dozens of SoC vendor engineers get started with coreboot in the last couple of years and they all came from kernel-style backgrounds (Linux, U-Boot or other projects using the same style). Of course there are also people coming from elsewhere, but I don't see kernel style becoming "unimportant" anytime soon. I'd bet 95+% of coreboot systems run Linux afterwards, and when adding support for new platforms it's just normal that the hardware vendor has the same people working on both kernel and firmware drivers for the same component.
On Tue, Jun 25, 2019 at 1:29 PM Julius Werner jwerner@chromium.org wrote:
The improvement of requiring a { on the ifs is known to
have positive impact; it's why Rust and Go both require it to my understanding.
How is this actually "known"?
Mandatory brackets are especially helpful when one makes quick debugging changes, say adding a print statement or an assignment and forgets to add the brackets to single statement clauses.
The compiler option would be useless if the debug code does not follow the indentation pattern.
-vb
Just out of curiosity, I checked the Google C++ style guide, but it doesn't really help:
In general, curly braces are not required for single-line statements, but they are allowed if you like them;
When I first started doing firmware, I was kind of annoyed having to go back and remove the braces from single line statements. It's kind of muscle memory to add them. I also don't have to think up front if I need them or not. And to Vadim's point, adding debug statements into a block is less error prone and less work if the braces are already there. For me, reading a diff where debug prints are added is easier if the braces were already there. Then I don't have to concern myself that I changed the condition.
e.g.,
/* Default to 4 KiB search space. */
if (req_size == 0)
if (req_size == 0) {debug("Using default size\n"); req_size = 4 * 1024;}
vs
/* Default to 4 KiB search space. */ if (req_size == 0) {
debug("Using default size\n"); req_size = 4 * 1024; }
But at the same time, I've grown accustomed to reading code like this:
if (table == NULL) return -1;
I guess I would opt for requiring braces.
On Tue, Jun 25, 2019 at 3:17 PM Vadim Bendebury vbendeb@chromium.org wrote:
On Tue, Jun 25, 2019 at 1:29 PM Julius Werner jwerner@chromium.org wrote:
The improvement of requiring a { on the ifs is known to
have positive impact; it's why Rust and Go both require it to my understanding.
How is this actually "known"?
Mandatory brackets are especially helpful when one makes quick debugging changes, say adding a print statement or an assignment and forgets to add the brackets to single statement clauses.
The compiler option would be useless if the debug code does not follow the indentation pattern.
-vb
coreboot mailing list -- coreboot@coreboot.org To unsubscribe send an email to coreboot-leave@coreboot.org
On Tue, Jun 25, 2019 at 1:29 PM Julius Werner jwerner@chromium.org wrote:
No we don't. We had a long discussion about multi-line comment styles some years back and I made the same argument there. ;)
you're totally right, oops! I misread the coding style again just a few days ago. Sheesh!
. I'd bet 95+% of coreboot systems run Linux afterwards, and when adding support for new platforms it's just normal that the hardware vendor has the same people working on both kernel and firmware drivers for the same component.
I'm sure you are absolutely correct here. That said, I'm starting to encounter folks from, e.g., the Rust community who find some aspects or our coding style odd. I'm expecting to see more of this. From personal experience, I can say that moving from Rust-based hypervisors, kernels, and firmware to coreboot is starting to feel a bit ... weird, and in this case, coreboot is the outlier.
But yeah, point taken that many people are working in the Linux kernel style nowadays ... OTOH, we have had our encounters with UeFi SyLe CoDe, and they could make a similar argument around code style ...
I'm still of the opinion that the addition of {} after if is a good idea. After years of Go and now Rust, seeing those unprotected bits of code after an if just scares me.
Thanks
ron
-
Jacob Garber -
Jonathan Neuschäfer -
Julius Werner -
Nico Huber -
Patrick Georgi -
Raul Rangel -
ron minnich -
Stefan Reinauer -
Vadim Bendebury