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by asveikau 2343 days ago
Not only that, but last I looked into this library's code there was a lot of undefined behavior and general sloppiness that goes against good C practices, eg. ignoring errors, casting all types to void * literally all the time or treating char VLAs as structs without regard for alignment.

My sympathy and respect to the author, but they did not appear learn C well before trying to "fix" it. It is kind of irresponsible, I think, to say it "aims to be production ready" and write it up as something other C neophytes may be interested in with some of these issues.
1 comments
shakna 2343 days ago
> Not only that, but last I looked into this library's code there was a lot of undefined behavior

Neither GCC's nor Clang's sanitisers pick up any undefined behaviour - and it's been like that for at least the last few years I've looked at it.

As to ignoring errors, and ignoring alignment, I don't think I've ever seen anything like that in the project. I have seen several pull requests delayed so that they will.

Overall, for what it's doing, this is one of the cleaner codebases I've dealt with.

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asveikau 2343 days ago 

    #define alloc_stack(T) ((struct T*)header_init( \
      (char[sizeof(struct Header) + sizeof(struct T)]){0}, T, AllocStack))
You can't take char[sizeof(foo)] on the stack and cast it to a foo*. malloc implementations for example are cafeul to align the buffer they give you. Windows, for example, aligns on 8 bytes. Probably popular alloca implementations do this too. For example, googling for "alloca alignment" finds some documentation: "... returns a void pointer to the allocated space, which is guaranteed to be suitably aligned for storage of any type of object". I have seen things break in the real world when these expectations are violated. The cello tree does this in a more few places since I last looked, eg. skimming it again I see the same pattern in the Windows stack trace code. It will probably work there but it's a coincidence, and not guaranteed by the standard AFAIK.

It looks like they got rid of some undefined things I saw when I looked in 2015. eg. they used to think you can do arithmetic on void pointers, which I think even gcc -Wall would flag for you. [Edit: Trying it out it seems I am wrong, on gcc and clang you need -pedantic to get that warning.]

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craftinator 2343 days ago
I'm really surprised that you both came up with opposing results... What tests were done indicating undefined behavior?
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