Re: [PATCH] perf annotate: Fix memcpy size in arch__grow_instructions

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Thu, Jan 22, 2026 at 10:27:27AM -0800, Ian Rogers wrote:
> On Thu, Jan 22, 2026 at 9:17 AM Suchit Karunakaran <suchitkarunakaran@gmail.com> wrote:

> > The memcpy in arch__grow_instructions() is copying the wrong number of
> > bytes when growing from a non-allocated table. It should copy
> > arch->nr_instructions * sizeof(struct ins) bytes, not just
> > arch->nr_instructions bytes.

> > This bug causes data corruption as only a partial copy of the
> > instruction table is made, leading to garbage data in most entries and
> > potential crashes

> > Signed-off-by: Suchit Karunakaran <suchitkarunakaran@gmail.com>
> > ---
> >  tools/perf/util/disasm.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)

> > diff --git a/tools/perf/util/disasm.c b/tools/perf/util/disasm.c
> > index 50b9433f3f8e..6faa9df8e373 100644
> > --- a/tools/perf/util/disasm.c
> > +++ b/tools/perf/util/disasm.c
> > @@ -81,7 +81,7 @@ static int arch__grow_instructions(struct arch *arch)
> >         if (new_instructions == NULL)
> >                 return -1;

> > -       memcpy(new_instructions, arch->instructions, arch->nr_instructions);
> > +       memcpy(new_instructions, arch->instructions, arch->nr_instructions * sizeof(struct ins));

> Reviewed-by: Ian Rogers <irogers@google.com>

> Nice catch! I think we've been trying to make code like this more like:
> memcpy(new_instructions, arch->instructions, arch->nr_instructions *
> sizeof(*new_instructions));
> but the immediately preceding calloc isn't doing this, so your patch
> is consistent. There is also a clean up in this code to switch to
> using reallocarray rather than realloc.

Right, that would be better, but the fix is good as is and we can
cleanup it later.

I added the missing:

Fixes: 2a1ff812c40be982 ("perf annotate: Introduce alternative method of keeping instructions table")

Its an old bug I introduced almost 10 years ago ;-\

- Arnaldo