llvm dev - May 2021 - Implementing "-Wstack-usage=" warning flag

Hello everyone,

I am trying to address the following bug:
https://bugs.llvm.org/show_bug.cgi?id=44418
Which asks for the implementation of the missing "-Wstack-usage="
which will report, on a per-function basis, if the stack usage exceeds the user
input.

My first approach at implementing "-Wstack-usage" is the following:
https://reviews.llvm.org/D101965
This is virtually identical to the output of "-Wframe-larger-than" on
clang. However when observing the behaviour of GCC I noticed that GCC outputs
different values for "-Wstack-usage" and
"-Wframe-larger-than".

This led me to my second approach which changes the way clang reports
"-Wframe-larger-than". This can be found here:
https://reviews.llvm.org/D101964
With this second approach, "-Wframe-larger-than" now reports the stack
size minus any space allocated on the stack for the parameters of called
functions. This more closely resembles GCC's behaviour.

I am unsure which implementation is preferred/correct and I am wondering if
anyone can comment or provide some information on what a better approach would
be, and what exactly the two flags should be reporting.

Thanks,
Ryan Santhirarajan
-------------- next part --------------
An HTML attachment was scrubbed...
URL:
<http://lists.llvm.org/pipermail/llvm-dev/attachments/20210506/1a75ef0a/attachment.html>

+Roman Lebedev

Roman - what was your particular motivation for filing the bug? Is
there a use case that -Wframe-larger-than doesn't cover? Would
-Wstack-usage as an alias for -Wframe-larger-than be adequate for your
use case (if directly using the existing flag is not sufficient for
some reason)?

On Wed, May 5, 2021 at 6:32 PM Ryan Santhirarajan via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
>
> Hello everyone,
>
>
>
> I am trying to address the following bug:
> https://bugs.llvm.org/show_bug.cgi?id=44418
>
> Which asks for the implementation of the missing “-Wstack-usage=” which
will report, on a per-function basis, if the stack usage exceeds the user input.
>
>
>
> My first approach at implementing “-Wstack-usage” is the following:
>
> https://reviews.llvm.org/D101965
>
> This is virtually identical to the output of “-Wframe-larger-than” on
clang. However when observing the behaviour of GCC I noticed that GCC outputs
different values for “-Wstack-usage” and “-Wframe-larger-than”.
>
>
>
> This led me to my second approach which changes the way clang reports
“-Wframe-larger-than”. This can be found here:
> https://reviews.llvm.org/D101964
>
> With this second approach, “-Wframe-larger-than” now reports the stack size
minus any space allocated on the stack for the parameters of called functions.
This more closely resembles GCC’s behaviour.
>
>
>
> I am unsure which implementation is preferred/correct and I am wondering if
anyone can comment or provide some information on what a better approach would
be, and what exactly the two flags should be reporting.
>
>
>
> Thanks,
>
> Ryan Santhirarajan
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev