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Date: Wed, 4 Oct 2023 09:02:57 +0200
From: Artem Savkov <asavkov@...hat.com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org,
netdev@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
linux-rt-users@...r.kernel.org, Jiri Olsa <jolsa@...nel.org>
Subject: Re: [RFC PATCH] tracing: change syscall number type in struct
syscall_trace_*
On Tue, Oct 03, 2023 at 03:11:15PM -0700, Andrii Nakryiko wrote:
> On Mon, Oct 2, 2023 at 6:53 AM Artem Savkov <asavkov@...hat.com> wrote:
> >
> > linux-rt-devel tree contains a patch that adds an extra member to struct
>
> can you please point to the patch itself that makes that change?
Of course, some context would be useful. The patch in question is b1773eac3f29c
("sched: Add support for lazy preemption") from rt-devel tree [0]. It came up
a couple of times before: [1] [2] [3] [4].
[0] https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/commit/?id=b1773eac3f29cbdcdfd16e0339f1a164066e9f71
[1] https://lore.kernel.org/linux-rt-users/20200221153541.681468-1-jolsa@kernel.org/t/#u
[2] https://github.com/iovisor/bpftrace/commit/a2e3d5dbc03ceb49b776cf5602d31896158844a7
[3] https://lore.kernel.org/bpf/xunyjzy64q9b.fsf@redhat.com/t/#u
[4] https://lore.kernel.org/bpf/20230727150647.397626-1-ykaliuta@redhat.com/t/#u
> > trace_entry. This causes the offset of args field in struct
> > trace_event_raw_sys_enter be different from the one in struct
> > syscall_trace_enter:
> >
> > struct trace_event_raw_sys_enter {
> > struct trace_entry ent; /* 0 12 */
> >
> > /* XXX last struct has 3 bytes of padding */
> > /* XXX 4 bytes hole, try to pack */
> >
> > long int id; /* 16 8 */
> > long unsigned int args[6]; /* 24 48 */
> > /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
> > char __data[]; /* 72 0 */
> >
> > /* size: 72, cachelines: 2, members: 4 */
> > /* sum members: 68, holes: 1, sum holes: 4 */
> > /* paddings: 1, sum paddings: 3 */
> > /* last cacheline: 8 bytes */
> > };
> >
> > struct syscall_trace_enter {
> > struct trace_entry ent; /* 0 12 */
> >
> > /* XXX last struct has 3 bytes of padding */
> >
> > int nr; /* 12 4 */
> > long unsigned int args[]; /* 16 0 */
> >
> > /* size: 16, cachelines: 1, members: 3 */
> > /* paddings: 1, sum paddings: 3 */
> > /* last cacheline: 16 bytes */
> > };
> >
> > This, in turn, causes perf_event_set_bpf_prog() fail while running bpf
> > test_profiler testcase because max_ctx_offset is calculated based on the
> > former struct, while off on the latter:
> >
> > 10488 if (is_tracepoint || is_syscall_tp) {
> > 10489 int off = trace_event_get_offsets(event->tp_event);
> > 10490
> > 10491 if (prog->aux->max_ctx_offset > off)
> > 10492 return -EACCES;
> > 10493 }
> >
> > This patch changes the type of nr member in syscall_trace_* structs to
> > be long so that "args" offset is equal to that in struct
> > trace_event_raw_sys_enter.
> >
> > Signed-off-by: Artem Savkov <asavkov@...hat.com>
> > ---
> > kernel/trace/trace.h | 4 ++--
> > kernel/trace/trace_syscalls.c | 7 ++++---
> > 2 files changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > index 77debe53f07cf..cd1d24df85364 100644
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -135,13 +135,13 @@ enum trace_type {
> > */
> > struct syscall_trace_enter {
> > struct trace_entry ent;
> > - int nr;
> > + long nr;
> > unsigned long args[];
> > };
> >
> > struct syscall_trace_exit {
> > struct trace_entry ent;
> > - int nr;
> > + long nr;
> > long ret;
> > };
> >
> > diff --git a/kernel/trace/trace_syscalls.c b/kernel/trace/trace_syscalls.c
> > index de753403cdafb..c26939119f2e4 100644
> > --- a/kernel/trace/trace_syscalls.c
> > +++ b/kernel/trace/trace_syscalls.c
> > @@ -101,7 +101,7 @@ find_syscall_meta(unsigned long syscall)
> > return NULL;
> > }
> >
> > -static struct syscall_metadata *syscall_nr_to_meta(int nr)
> > +static struct syscall_metadata *syscall_nr_to_meta(long nr)
> > {
> > if (IS_ENABLED(CONFIG_HAVE_SPARSE_SYSCALL_NR))
> > return xa_load(&syscalls_metadata_sparse, (unsigned long)nr);
> > @@ -132,7 +132,8 @@ print_syscall_enter(struct trace_iterator *iter, int flags,
> > struct trace_entry *ent = iter->ent;
> > struct syscall_trace_enter *trace;
> > struct syscall_metadata *entry;
> > - int i, syscall;
> > + int i;
> > + long syscall;
> >
> > trace = (typeof(trace))ent;
> > syscall = trace->nr;
> > @@ -177,7 +178,7 @@ print_syscall_exit(struct trace_iterator *iter, int flags,
> > struct trace_seq *s = &iter->seq;
> > struct trace_entry *ent = iter->ent;
> > struct syscall_trace_exit *trace;
> > - int syscall;
> > + long syscall;
> > struct syscall_metadata *entry;
> >
> > trace = (typeof(trace))ent;
> > --
> > 2.41.0
> >
> >
>
--
Artem
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