[LLVMdev] Adding a stack probe function attribute

[Reid Kleckner]

Yeah, the function attributes section of LangRef is a reasonable place to
put stuff like this:
http://llvm.org/docs/LangRef.html#function-attributes

I think we should add this. I also know that LLILAC needs something like
this as well. I propose the following:
- Add a string attribute called "stack-probe-symbol"="foo".
- The presence of this attribute indicates that stack probes should be
emitted, even on non-Windows OSs.
- (future work) For LLILAC, if this attribute is present but the string is
empty, this can be a signal that the check must be emitted inline, either
as a sequence of stores or a loop.

This also addresses David's concern with the hardcoded __probestack symbol
name.

On Sun, Jul 26, 2015 at 2:23 AM, John Kåre Alsaker <
john.mailinglists at gmail.com> wrote:

> Since David Majnemer doesn't seem overly eager to merge my patches,
> let's see if we can't figure things out here.
>
> I noticed a string function attribute appeared in LangRef.rst, would
> that be the correct place to document this?
>
> For reference:
> http://reviews.llvm.org/D9653
> http://reviews.llvm.org/D9654
> http://reviews.llvm.org/D9858
>
> On Wed, Aug 6, 2014 at 5:34 PM, John Kåre Alsaker
> <john.mailinglists at gmail.com> wrote:
> > I updated http://reviews.llvm.org/D4717 and also wrote an __probestack
> > implementation:
> > https://github.com/Zoxc/compiler-rt/compare/llvm-mirror:master...stprobe
> >
> > Which instruction would be the preferable one to probe with? I used OR
> since
> > that's what GCC/libgcc does, but I don't see why that would be better
> than a
> > write.
> >
> >
> >
> > On Tue, Aug 5, 2014 at 7:34 PM, Reid Kleckner <rnk at google.com> wrote:
> >>
> >> On Tue, Aug 5, 2014 at 8:53 AM, John Kåre Alsaker
> >> <john.mailinglists at gmail.com> wrote:
> >>>
> >>> Would the __probestack functions be a suitable addition to compiler-rt?
> >>> Does it already have __chkstk or is that provided by something else on
> >>> Windows? I noticed that libgcc implemented them in cygwin.S.
> >>
> >>
> >> It seems reasonable to put them in compiler-rt/lib/builtins.
> >>
> >> I don't think anyone is currently using compiler-rt's builtins on
> Windows,
> >> so it doesn't have __chkstk. Typically that is provided by the Cygwin,
> >> MinGW, or MSVC C runtime.
> >
> >
>
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