Yonghong, can you send a PR for your branch?
On Tue, Jun 6, 2017 at 12:20 AM, Y Song via iovisor-dev <
iovisor-dev@lists.iovisor.org> wrote:
> Hi, Tetsuo,
>
> You are right. The bug is actually introduced by my last patch. I just
> focused one aspect of issue and inadvertently introduced another
> *blocker* bug.
>
> I just pushed a patch. Thanks a lot for reporting the issue and
> testing out the fix.
>
> Yonghong
>
> On Mon, Jun 5, 2017 at 5:25 PM, Tetsuo Handa
> <penguin-ker...@i-love.sakura.ne.jp> wrote:
> > Hello.
> >
> > I changed the hook as below and confirmed that cp == NULL at
> bpf_probe_read().
> > That is, it is bpf_usdt_readarg() which got broken.
> >
> > ----------
> > int do_start(struct pt_regs *ctx) {
> > char *cp = NULL;
> > bpf_usdt_readarg(1, ctx, &cp);
> > struct { char query[QUERY_MAX]; } data = { };
> > if (cp != NULL)
> > bpf_probe_read(&data.query, sizeof(data.query), (void *) cp);
> > else
> > data.query[0] = '!';
> > events.perf_submit(ctx, &data, sizeof(data));
> > return 0;
> > };
> > ----------
> >
> > If I do
> >
> > - std::string cptr = tfm::format("*((volatile %s *)dest)", ctype);
> > + std::string cptr = tfm::format("*((%s *)dest)", ctype);
> >
> > (i.e. drop only "volatile " part) in that commit like below
> >
> > ----------
> > diff --git a/src/cc/usdt.cc b/src/cc/usdt.cc
> > --- a/src/cc/usdt.cc
> > +++ b/src/cc/usdt.cc
> > @@ -152,7 +152,7 @@ bool Probe::usdt_getarg(std::ostream &stream) {
> >
> > for (size_t arg_n = 0; arg_n < arg_count; ++arg_n) {
> > std::string ctype = largest_arg_type(arg_n);
> > - std::string cptr("dest");
> > + std::string cptr = tfm::format("*((%s *)dest)", ctype);
> >
> > tfm::format(stream,
> > "static __always_inline int _bpf_readarg_%s_%d("
> > ----------
> >
> > USDT probe works again as well as build warning shown below goes away.
> >
> > ----------
> > /virtual/main.c:4:8: warning: incompatible integer to pointer conversion
> assigning to 'void *' from 'volatile uint64_t' (aka 'volatile unsigned long
> long') [-Wint-conversion]
> > dest = *(volatile uint64_t *)&ctx->bx;
> > ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > ----------
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