On Mon, Aug 28, 2023 at 08:57:21AM +0800, Rong Tao wrote:
> Hi, jirka. Thanks for your reply.
>
> > > @@ -164,13 +165,14 @@ int main(int argc, char **argv)
> > > }
> > >
> > > /* initialize kernel symbol translation */
> > > - if (load_kallsyms()) {
> > > + ksyms = load_kallsyms();
> >
> > if we keep the load_kallsyms/ksym_search/ksym_get_addr functions as described
> > in [1] the samples/bpf would stay untouched apart from the Makefile change
>
> Maybe we should make this modification, wouldn't it be better? After all,
> not modifying the source code of samples/bpf is not really a reason not to
> make modifications to load_kallsyms(), what do you think?
I think we want separate selftest and samples changes and I don't see
other way to do that
>
> In addition, if we continue to keep the original ksym_search() interface,
> the following problems are very difficult to deal with:
>
> Source code ksym_search [1]
>
> struct ksym *ksym_search(long key)
> {
> int start = 0, end = sym_cnt;
> int result;
>
> /* kallsyms not loaded. return NULL */
> if (sym_cnt <= 0)
> return NULL;
>
> while (start < end) {
> size_t mid = start + (end - start) / 2;
>
> result = key - syms[mid].addr;
> if (result < 0)
> end = mid;
> else if (result > 0)
> start = mid + 1;
> else
> return &syms[mid]; <<<
> }
>
> if (start >= 1 && syms[start - 1].addr < key &&
> key < syms[start].addr)
> /* valid ksym */
> return &syms[start - 1]; <<<
>
> /* out of range. return _stext */
> return &syms[0]; <<<
> }
>
> The original ksym_search() interface directly returns the global syms
> address, which is also dangerous for multi-threading. If we allocate new
> memory for this, it is not a perfect solution.
the assumption was that the original ksym_search touches the global
syms allocated before running tests.. then tests that actually need
fresh kallsyms data (because of bpf_testmod load/unload) would get
their own copy of kallsyms
jirka
>
> If we rewrite
>
> struct ksym *ksym_search(long key)
>
> to
> struct ksym ksym_search(long key)
>
> This also affects the source code in samples/bpf.
>
> The same problem exists with ksym_get_addr().
>
> Best wishes,
> Rong Tao
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/trace_helpers.c#n100
>
>
