Re: Stack analysis tool that really work?

From	Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups	comp.arch.embedded
Subject	Re: Stack analysis tool that really work?
Date	2021-08-07 19:50 +0300
Organization	Tidorum Ltd
Message-ID	<in7rubFipjuU1@mid.individual.net> (permalink)
References	(10 earlier) <seiqoj$8mk$1@dont-email.me> <in5iifF4i5gU1@mid.individual.net> <sekf60$uvl$1@dont-email.me> <in77v3FeoomU1@mid.individual.net> <sem7o3$v1d$1@dont-email.me>

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On 2021-08-07 18:09, Don Y wrote:
> On 8/7/2021 4:09 AM, Niklas Holsti wrote:

(On how the Bound-T tool models instructions for stack and WCET analysis:)

>> The internal model includes not only the cost of the instruction, but 
>> also its effect on the computation. For example, an instruction like 
>> "increment the accumulator", INC A, would be decoded into a model that 
>> says
>>
>>      WCET: 1 cycle.
>>      Control flow: to next instruction, unconditional.
>>      Effect: A := A + 1.
>>
>> and also the effect, if any, on condition flags.
> 
> Why do you care about the "effect"?  Are you trying to determine
> which branches will be taken?  How many iterations through loops?
> etc.

The effect is necessary for any analysis that depends on run-time 
values. Loop bounds are the prime example for WCET analysis, but 
stack-usage analysis also needs it. For example, the effect of a push 
instruction is to increment the "local stack height" model variable by 
some number that reflects the size of the pushed data (which size can, 
in principle, be non-static and computed at run time).

The stack-usage analysis finds the maximum possible value of the local 
stack height in each subprogram, both globally and at each call site 
within the subprogram, then adds up the local stack heights along each 
possible call path to find the total usage for that call path, and then 
finds and reports the path with the largest total usage.

> Doesn't this require a fairly complete model of the processor?

Yes indeed. The model could be somewhat simpler for stack-usage analysis 
than for WCET analysis. For stack usage, the relevant effect of an 
instruction is just to increase or decrease the local stack height by a 
static constant. If push/pop happens in loops they are usually balanced 
so that a loop iteration has no net effect on stack usage, making loop 
iteration bounds unnecessary.

> My "cost constrained" days were back in the days of the "small/cheap
> CPU" where you had to predict performance accurately -- but, doing so
> was relatively easy (because processors had very predictable
> instruction execution times).

And that is the kind of processor that Bound-T was designed to support 
for WCET analysis. Stack-usage analysis is not so sensitive.

Thread

Stack analysis tool that really work? pozz <pozzugno@gmail.com> - 2021-07-29 18:22 +0200
  Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-07-29 19:36 +0300
  Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-02 17:56 -0700
    Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-03 11:43 +0300
      Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-03 02:28 -0700
        Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-04 22:14 +0300
          Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-04 15:43 -0700
    Re: Stack analysis tool that really work? pozz <pozzugno@gmail.com> - 2021-08-03 11:49 +0200
      Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-03 20:17 -0700
        Re: Stack analysis tool that really work? pozz <pozzugno@gmail.com> - 2021-08-04 16:43 +0200
          Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-04 11:06 -0700
            Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-05 12:00 +0300
              Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-05 04:54 -0700
      Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-04 20:00 +0300
        Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-04 10:50 -0700
          Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-04 21:50 +0300
            Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-04 15:46 -0700
              Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-05 13:43 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-05 06:16 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-05 18:39 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-06 01:09 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-06 22:58 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-06 16:04 -0700
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-06 16:06 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-07 14:20 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-07 10:26 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-07 20:46 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-07 15:14 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-07 14:09 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-07 08:09 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-07 19:50 +0300
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-07 20:02 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-07 10:34 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-07 21:10 +0300
                Re: Stack analysis tool that really work? George Neuner <gneuner2@comcast.net> - 2021-08-06 22:55 -0400
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-07 13:40 +0300
                Re: Stack analysis tool that really work? George Neuner <gneuner2@comcast.net> - 2021-08-08 18:34 -0400
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-09 10:50 +0300
                Re: Stack analysis tool that really work? Paul Rubin <no.email@nospam.invalid> - 2021-08-09 11:26 -0700
                Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-09 22:59 +0300
                Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-09 12:04 -0700
          Re: Stack analysis tool that really work? Niklas Holsti <niklas.holsti@tidorum.invalid> - 2021-08-05 13:18 +0300
            Re: Stack analysis tool that really work? Don Y <blockedofcourse@foo.invalid> - 2021-08-05 04:59 -0700

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