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

[Ian Rogers]

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?

Thanks,
Ian

> v5 changes)
>
>  * add a cleanup patch
>  * add is_union and is_flex_array fields to find member correctly
>
> v4: https://lore.kernel.org/r/20260916061926.2224222-1-namhyung@xxxxxxxxxx/
>
>  * update last member even if the offset is same
>  * handle type qualifiers in die_has_flex_array()
>  * add zero-length array members as flexible arrays
>  * check return value of strbuf_init() for type name
>
> v3: https://lore.kernel.org/r/20260915064035.1970175-1-namhyung@xxxxxxxxxx
>
>  * patch 1 was merged!
>  * check if last member is found
>  * check member location when finding flex-array
>  * ensure member typename is initiailized
>  * fix a bug to pass a wrong type in check_variable()
>  * fix a typo in a comment
>
> v2: https://lore.kernel.org/r/20260914064535.1671939-1-namhyung@xxxxxxxxxx
>
>  * fix missing index increment in the histogram
>  * support flex array in union types
>  * add recursion check in die_has_flex_array()
>  * check negative index arrays properly
>  * avoid divide-by-zero when the size is unknown
>
> v1: https://lore.kernel.org/r/20260912054706.1475583-1-namhyung@xxxxxxxxxx
>
> Thanks,
> Namhyung
>
>
> Cc: Zecheng Li <zli94@xxxxxxxx>
> Cc: Yanbo Zhao <yzhao62@xxxxxxxx>
> Cc: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
> Cc: Shuai Xue <xueshuai@xxxxxxxxxxxxxxxxx>
>
> Namhyung Kim (4):
>   perf dwarf-aux: Add die_has_flex_array() helper
>   perf annotate-data: A small cleanup in __add_member_cb()
>   perf annotate-data: Allow out-of-size access for flex-array types
>   perf annotate-data: Adjust type offset for flex-array
>
>  tools/perf/util/annotate-data.c | 192 ++++++++++++++++++++++++--------
>  tools/perf/util/annotate-data.h |   6 +
>  tools/perf/util/dwarf-aux.c     | 107 ++++++++++++++++++
>  tools/perf/util/dwarf-aux.h     |   3 +
>  4 files changed, 262 insertions(+), 46 deletions(-)
>
> --
> 2.55.0
>