On Fri, Dec 2, 2022 at 7:39 AM Timo Hunziker <timo.hunziker@xxxxxx> wrote: > > Parse USDT arguments like "8@(%rsp)" on x86. These are emmited by > systemtap. The syntax is a mixture between the "memory dereference > case" and the "register read case" as the offset is zero but the > register is wrapped in parentheses. We treat them the same as the > the "register read case". wait, why? I'd assume this is equivalent to 8@0(%rsp) and that's actually the USDT_ARG_REG_DEREF case? I.e., we read the value of %rsp and then use that as a pointer to a memory. > > I've tested that this fixes the "unrecognized arg #N spec: 8@(%rsp).." > error I've run into when attaching to a probe with such an argument. > Attaching and reading the arguments works. > > Something similar might be needed for the other supported > architectures. > > ref: https://github.com/libbpf/libbpf/issues/559 > > Signed-off-by: Timo Hunziker <timo.hunziker@xxxxxx> > --- > tools/lib/bpf/usdt.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c > index b8daae265f99..5e7ec7ad8ad7 100644 > --- a/tools/lib/bpf/usdt.c > +++ b/tools/lib/bpf/usdt.c > @@ -1233,6 +1233,14 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec > if (reg_off < 0) > return reg_off; > arg->reg_off = reg_off; > + } else if (sscanf(arg_str, " %d @ ( %%%15[^)] ) %n", &arg_sz, reg_name, &len) == 2) { > + /* Register read case with parentheses, e.g., 8@(%rsp) */ > + arg->arg_type = USDT_ARG_REG; while you implemented it as "return %rsp value", it's a very different case > + arg->val_off = 0; > + reg_off = calc_pt_regs_off(reg_name); > + if (reg_off < 0) > + return reg_off; > + arg->reg_off = reg_off; > } else if (sscanf(arg_str, " %d @ %%%15s %n", &arg_sz, reg_name, &len) == 2) { > /* Register read case, e.g., -4@%eax */ > arg->arg_type = USDT_ARG_REG; > -- > 2.36.2 >
