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Message-ID: <20231012094444.0967fa79@gandalf.local.home> Date: Thu, 12 Oct 2023 09:44:44 -0400 From: Steven Rostedt <rostedt@...dmis.org> To: Artem Savkov <asavkov@...hat.com> Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, bpf@...r.kernel.org, netdev@...r.kernel.org, Masami Hiramatsu <mhiramat@...nel.org>, linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, linux-rt-users@...r.kernel.org, Jiri Olsa <jolsa@...nel.org> Subject: Re: [RFC PATCH bpf-next] bpf: change syscall_nr type to int in struct syscall_tp_t On Thu, 12 Oct 2023 13:45:50 +0200 Artem Savkov <asavkov@...hat.com> wrote: > linux-rt-devel tree contains a patch (b1773eac3f29c ("sched: Add support > for lazy preemption")) that adds an extra member to struct 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 } > > What bpf program is actually getting is a pointer to struct > syscall_tp_t, defined in kernel/trace/trace_syscalls.c. This patch fixes > the problem by aligning struct syscall_tp_t with with struct > syscall_trace_(enter|exit) and changing the tests to use these structs > to dereference context. > > Signed-off-by: Artem Savkov <asavkov@...hat.com> Thanks for doing a proper fix. Acked-by: Steven Rostedt (Google) <rostedt@...dmis.org> -- Steve
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