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Comment by gpderetta | Hacker News Reader

Exactly.

For example there were programs 30-40 years ago that relied on exact stack layouts. These days everybody would agree they are completely broken.

The issue of course is that it is extremely hard to write programs that have no UB. It would be nice for compilers to have an option to automatically introduce assetions whenever they rely on some UB-derived axiom, basically as a sort of lightweight sanitizer.

In fact if we had sanitizers 30-40 years ago probably things would be better today.

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> It would be nice for compilers to have an option to automatically introduce assetions whenever they rely on some UB-derived axiom

Modifying a value from a different thread without synchronization is UB. The compiler assumes this does not happen in order to e.g. move things into registers. Could you elaborate how (and how often) you would like to have this kind of UB-derived axiom ("this value remains the same from here to there") checked with assertions?

Obviously you wouldn't be able to catch many, or even most cases. Use-after-free is another case that would be very expensive to detect.

I was using it in 2000,

https://www.parasoft.com/products/parasoft-insure/

21 years later it is still an uphill battle to adopt such technology in C and C++ projects.

We had sanitizers since C exists, 1979 to be more exact.

"Although the first edition of K&R described most of the rules that brought C's type structure to its present form, many programs written in the older, more relaxed style persisted, and so did compilers that tolerated it. To encourage people to pay more attention to the official language rules, to detect legal but suspicious constructions, and to help find interface mismatches undetectable with simple mechanisms for separate compilation, Steve Johnson adapted his pcc compiler to produce lint [Johnson 79b], which scanned a set of files and remarked on dubious constructions. "

-- https://www.bell-labs.com/usr/dmr/www/chist.html

I was going to add "in open source compilers" to hedge my statement :).

That seems to be a static analysis tool though (which generally have not been great). Did it also inject runtime checks?

No, but still not even that gets the love it deserve.

And a famous commercial variant of it has been PC-lint from https://www.gimpel.com/.

Being available on open source compilers does little to change the culture, as per latest surveys only 11% of developers care to use any kind of tooling for improving their code quality in C and C++.

At CppCon a couple of years ago, only about 1% of the audience answered positively to Herb Sutters' question.

Those numbers are indeed a bit depressing.

Here is a recent survey, with a more positive number of about 37%, see question 10.

https://isocpp.org/files/papers/CppDevSurvey-2021-04-summary...

That's good example, because nobody would complain if stack layouts changed and those programs failed. But if the compiler chooses to "optimize away" checks on stack layout, that's a different thing altogether. Also note that if you use pthreads or Linux clone or you are writing an operating system you can need to rely on exact stack layouts even today.

Stack layouts are only really relevant at ABI boundaries. In these cases the layout is usually specified in extensions to C or in other ways, such as handwritten assembly.

Linux clone, pthreads, and os code commonly look at stack boundaries

Not sure what you are referring to with stack boundaries. Of course the ABI imposes some minimal requirements at ABI visible points, but these days you can't even rely on the existence of frame pointers to traverse the stack and you have to use the DWARF unwind machinery. And the content of the stack frame itself is completely unspecified of course.

So I create a thread with a custom stack which is an allocated buffer. At the top, I write a sequence of bytes in some order. Then I periodically read the top of the stack to see if the stack is getting close to overflow. Meanwhile, the thread code is also addressing the same store.

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