On Fri, Jul 11, 2025 at 7:25 AM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Thu, Jul 10, 2025 at 12:10 AM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
> >
> > For now, we lookup the address of the attach target in
> > bpf_check_attach_target() with find_kallsyms_symbol_value or
> > kallsyms_lookup_name, which is not accurate in some cases.
> >
> > For example, we want to attach to the target "t_next", but there are
> > multiple symbols with the name "t_next" exist in the kallsyms, which makes
> > the attach target ambiguous, and the attach should fail.
> >
> > Introduce the function bpf_lookup_attach_addr() to do the address lookup,
> > which will return -EADDRNOTAVAIL when the symbol is not unique.
> >
> > We can do the testing with following shell:
> >
> > for s in $(cat /proc/kallsyms | awk '{print $3}' | sort | uniq -d)
> > do
> > if grep -q "^$s\$" /sys/kernel/debug/tracing/available_filter_functions
> > then
> > bpftrace -e "fentry:$s {printf(\"1\");}" -v
> > fi
> > done
> >
> > The script will find all the duplicated symbols in /proc/kallsyms, which
> > is also in /sys/kernel/debug/tracing/available_filter_functions, and
> > attach them with bpftrace.
> >
> > After this patch, all the attaching fail with the error:
> >
> > The address of function xxx cannot be found
> > or
> > No BTF found for xxx
> >
> > Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
> > ---
> > v3:
> > - reject all the duplicated symbols
> > v2:
> > - Lookup both vmlinux and modules symbols when mod is NULL, just like
> > kallsyms_lookup_name().
> >
> > If the btf is not a modules, shouldn't we lookup on the vmlinux only?
> > I'm not sure if we should keep the same logic with
> > kallsyms_lookup_name().
> >
> > - Return the kernel symbol that don't have ftrace location if the symbols
> > with ftrace location are not available
> > ---
> > kernel/bpf/verifier.c | 71 ++++++++++++++++++++++++++++++++++++++++---
> > 1 file changed, 66 insertions(+), 5 deletions(-)
> >
> > diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
> > index 53007182b46b..bf4951154605 100644
> > --- a/kernel/bpf/verifier.c
> > +++ b/kernel/bpf/verifier.c
> > @@ -23476,6 +23476,67 @@ static int check_non_sleepable_error_inject(u32 btf_id)
> > return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id);
> > }
> >
> > +struct symbol_lookup_ctx {
> > + const char *name;
> > + unsigned long addr;
> > +};
> > +
> > +static int symbol_callback(void *data, unsigned long addr)
> > +{
> > + struct symbol_lookup_ctx *ctx = data;
> > +
> > + if (ctx->addr)
> > + return -EADDRNOTAVAIL;
>
> #define ENOTUNIQ 76 /* Name not unique on network */
>
> fits a bit better, no?
Yeah, this looks much better. I'll use it instead of
EADDRNOTAVAIL in the next version.
Thanks!
Menglong Dong
>
> > + ctx->addr = addr;
> > +
> > + return 0;
> > +}
> > +
>
> [...]
