Re: [PATCH v5 0/4] perf annotate-data: Support flexible array types

[Ian Rogers]

On Sat, Sep 19, 2026 at 10:56 AM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> On Sat, Sep 19, 2026 at 09:18:55AM -0700, Ian Rogers wrote:
> > On Fri, Sep 18, 2026 at 11:37 PM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
> > >
> > > Hello,
> > >
> > > The flexible arrays are dynamically allocated with different size.  So checking
> > > with the original type size won't match and cannot find the type if the offset
> > > is bigger than the size.  This patch series detects those flex-arrays and allows
> > > accesses beyong the original size.
> > >
> > > I'm not sure what's the best way to add test codes for data type profiling as it
> > > seems we need to add a lot more workloads for different cases.  Probably we may
> > > want to split the workloads as separate binaries.
> >
> > We have tools/perf/tests/shell/data_type_profiling.sh, I wonder can we
> > not just have some workload with a:
> > ```
> > struct flex_array {
> >    int len;
> >    int vals[];
> > };
> > ```
> > then create a randomly sized flex array and access  it in a loop something like:
> > ```
> > struct flex_array *a = calloc(sizeof(*a) + random_number * sizeof(int));
> > a->len = random_number;
> > while (!done) { /* done is set by an alarm like with noploop */
> >    for (int i = 0; i < a->len; i++) {
> >        a[i]++; /* Expect blame on struct flex_array here */
> >    }
> > }
> > ```
> > ensuring the type profile blames the struct flex_array?
>
> Sure, I can add that.
>
> But I was afraid it'd need many small workloads to check data type
> profiling behavior for different aspects.  Maybe we can think about it
> later when we need more. :)

Agreed, there may be a way to automate that. For the specific bug
where flex arrays fail to get type profiles we should be able to avoid
reproducing it with a simple test.

Thanks!
Ian

> Thanks,
> Namhyung
>