On Mon, Feb 24, 2025 at 03:57:55PM -0800, Ihor Solodrai wrote: > Information about USDT argument size is implicitly stored in > __bpf_usdt_arg_spec, but currently it's not accessbile to BPF programs > that use USDT. > > Implement bpf_sdt_arg_size() that returns the size of an USDT argument > in bytes. > > v1->v2: > * do not add __bpf_usdt_arg_spec() helper Reviewed-by: Jiri Olsa <jolsa@xxxxxxxxxx> jirka > > v1: https://lore.kernel.org/bpf/20250220215904.3362709-1-ihor.solodrai@xxxxxxxxx/ > > Suggested-by: Andrii Nakryiko <andrii@xxxxxxxxxx> > Signed-off-by: Ihor Solodrai <ihor.solodrai@xxxxxxxxx> > --- > tools/lib/bpf/usdt.bpf.h | 32 ++++++++++++++++++++++++++++++++ > 1 file changed, 32 insertions(+) > > diff --git a/tools/lib/bpf/usdt.bpf.h b/tools/lib/bpf/usdt.bpf.h > index b811f754939f..2a7865c8e3fe 100644 > --- a/tools/lib/bpf/usdt.bpf.h > +++ b/tools/lib/bpf/usdt.bpf.h > @@ -108,6 +108,38 @@ int bpf_usdt_arg_cnt(struct pt_regs *ctx) > return spec->arg_cnt; > } > > +/* Returns the size in bytes of the #*arg_num* (zero-indexed) USDT argument. > + * Returns negative error if argument is not found or arg_num is invalid. > + */ > +static __always_inline > +int bpf_usdt_arg_size(struct pt_regs *ctx, __u64 arg_num) > +{ > + struct __bpf_usdt_arg_spec *arg_spec; > + struct __bpf_usdt_spec *spec; > + int spec_id; > + > + spec_id = __bpf_usdt_spec_id(ctx); > + if (spec_id < 0) > + return -ESRCH; > + > + spec = bpf_map_lookup_elem(&__bpf_usdt_specs, &spec_id); > + if (!spec) > + return -ESRCH; > + > + if (arg_num >= BPF_USDT_MAX_ARG_CNT) > + return -ENOENT; > + barrier_var(arg_num); > + if (arg_num >= spec->arg_cnt) > + return -ENOENT; > + > + arg_spec = &spec->args[arg_num]; > + > + /* arg_spec->arg_bitshift = 64 - arg_sz * 8 > + * so: arg_sz = (64 - arg_spec->arg_bitshift) / 8 > + */ > + return (unsigned int)(64 - arg_spec->arg_bitshift) / 8; > +} > + > /* Fetch USDT argument #*arg_num* (zero-indexed) and put its value into *res. > * Returns 0 on success; negative error, otherwise. > * On error *res is guaranteed to be set to zero. > -- > 2.48.1 > >
