[lttng-dev] [MODULES RFC PATCH] Extract the bitmask of FDs set in select syscall

[Julien Desfossez]

Instead of extracting the user-space pointers of the 3 fd_set, we now
extract the bitmask of the FDs in the sets (in, out, ex) in the form of
an array of unsigned long (1024 FDs is the limit in the kernel).

In this example, we select in input FDs 3, 5 and 10 (0x428), it returns
that one FD is ready: FD 10 (0x400).

syscall_entry_select: { n = 11,
	_fdset_in_length = 1, fdset_in = [ [0] = 0x428 ],
	_fdset_out_length = 1, fdset_out = [ [0] = 0x0 ],
	_fdset_ex_length = 0, fdset_ex = [ ],
	tvp = 0
}
syscall_exit_select: { ret = 1,
	_fdset_in_length = 1, fdset_in = [ [0] = 0x400 ],
	_fdset_out_length = 1, fdset_out = [ [0] = 0x0 ],
	_fdset_ex_length = 0, fdset_ex = [ ],
	tvp = 0
}

Signed-off-by: Julien Desfossez <jdesfossez at efficios.com>
---
 .../x86-64-syscalls-3.10.0-rc7_pointers_override.h | 56 ++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/instrumentation/syscalls/headers/x86-64-syscalls-3.10.0-rc7_pointers_override.h b/instrumentation/syscalls/headers/x86-64-syscalls-3.10.0-rc7_pointers_override.h
index 702cfb5..23ffbdd 100644
--- a/instrumentation/syscalls/headers/x86-64-syscalls-3.10.0-rc7_pointers_override.h
+++ b/instrumentation/syscalls/headers/x86-64-syscalls-3.10.0-rc7_pointers_override.h
@@ -115,6 +115,62 @@ SC_LTTNG_TRACEPOINT_EVENT(pipe,
 	)
 )
 
+#define OVERRIDE_64_select
+SC_LTTNG_TRACEPOINT_EVENT_CODE(select,
+	TP_PROTO(sc_exit(long ret,) int n, fd_set __user * inp, fd_set __user * outp,
+		fd_set __user * exp, struct timeval * tvp),
+	TP_ARGS(sc_exit(ret,) n, inp, outp, exp, tvp),
+	TP_locvar(
+		unsigned long fds_in[__FD_SETSIZE / (8 * sizeof(long))],
+			fds_out[__FD_SETSIZE / (8 * sizeof(long))],
+			fds_ex[__FD_SETSIZE / (8 * sizeof(long))];
+		int nb_in, nb_out, nb_ex;
+	),
+	TP_code(
+		sc_inout(
+		{
+			unsigned long nr;
+			int ret;
+
+			nr = FDS_BYTES(n);
+			tp_locvar->nb_in = 0;
+			tp_locvar->nb_out = 0;
+			tp_locvar->nb_ex = 0;
+			if (inp) {
+				ret = copy_from_user(tp_locvar->fds_in, inp, nr);
+				if (ret < 0)
+					goto skip_code;
+				tp_locvar->nb_in = nr/sizeof(long);
+			}
+			if (outp) {
+				ret = copy_from_user(tp_locvar->fds_out, outp, nr);
+				if (ret < 0)
+				goto skip_code;
+				tp_locvar->nb_out = nr/sizeof(long);
+			}
+			if (exp) {
+				ret = copy_from_user(tp_locvar->fds_ex, exp, nr);
+				if (ret < 0)
+					goto skip_code;
+				tp_locvar->nb_ex = nr/sizeof(long);
+			}
+		}
+		skip_code:
+		)
+	),
+	TP_FIELDS(
+		sc_exit(ctf_integer(long, ret, ret))
+		sc_in(ctf_integer(int, n, n))
+		sc_inout(ctf_sequence_hex(unsigned long, fdset_in,
+				&tp_locvar->fds_in, unsigned long, tp_locvar->nb_in))
+		sc_inout(ctf_sequence_hex(unsigned long, fdset_out,
+				&tp_locvar->fds_out, unsigned long, tp_locvar->nb_out))
+		sc_inout(ctf_sequence_hex(unsigned long, fdset_ex,
+				&tp_locvar->fds_ex, unsigned long, tp_locvar->nb_ex))
+		sc_inout(ctf_integer(struct timeval *, tvp, tvp))
+	)
+)
+
 #else	/* CREATE_SYSCALL_TABLE */
 
 #define OVERRIDE_TABLE_64_clone
-- 
1.9.1