__chkstk in debug and release-safe modes only and on all OSes

[andrewrk]

__chkstk is a great idea, it causes a stack overflow to become a segfault. Let's do it on all OSes that we can, not just windows.

And let's turn it off for ReleaseFast mode.

[PavelVozenilek]

Stack size should large enough by default (say 10 MB instead of MSVC's 1 MB). For embedded application one could always set it lower.

Certain version of AIX C++ compiler had default stack size 40 kB (yes, kilobytes) and it was big pain to find out why program (working elsewhere else) crashed.

[andrewrk]

Stack size should large enough by default

Large enough for what?

You could have a recursive function use 9.9 MB and then call a function with a greater-than-page-size stack frame.

Edge cases matter.

[PavelVozenilek]

Large enough for big applications. LLVM itself uses 10 MB stack. I set it to 20 MB, to keep troubles away. I had never run out of stack due to recursion.

Edit: I do not think __chkstk is bad or anything, it just is not a problem I got. (Though: I had once a silly idea to replace C stdlib from MSVC with something leaner. Minimal size executables and such. Handling these internal and undocumented functions took lot of time and I eventually abandoned the attempt, due to random crashes.)

[kyle-github]

Hi @PavelVozenilek, I am not sure I get the point of your comment. Stack is not actually allocated from main memory except on demand. The __chkstk function just makes sure that the local allocation of each function does not go past the guard page. It has nothing to do with the total amount of virtual memory address space that is allocated for the stack. Am I missing something???

I do like __chkstk. While I tend not to use large on-stack data, there is code that does with good effect. It is a great way to handle allocation without using malloc in C if your use cases can handle that approach.

[kyle-github]

I did not run across an alloca() equivalent in Zig. If there is not, is stack allocation known statically on each function invocation at compile time? If so, then you could inject the equivalent of __chkstk only when you knew that there was a lot of data in the function's activation record.

[PavelVozenilek]

@kyle-github: I made aside remark, about usefullness of setting large stack limit.

[andrewrk]

then you could inject the equivalent of __chkstk only when you knew that there was a lot of data in the function's activation record.

Status quo: when targeting windows, LLVM emits a call to __chkstk when the stack frame is larger than the guard page size, in all build modes.

[kyle-github]

@andrewrk, cool.

[andrewrk]

I did not run across an alloca() equivalent in Zig.

See #225

[kyle-github]

@andrewrk, Ah missed that one. Thanks. While alloca() is useful in some circumstances, it is easily abused.

[andrewrk]

Looks like "probe-stack" is relevant: http://llvm.org/docs/LangRef.html#function-attributes