From: Dmitry V. Levin <ldv@altlinux.org>
Date: Wed, 8 Jul 2015 14:10:56 +0000 (+0000)
Subject: Implement RVAL_DECODED flag
X-Git-Tag: v4.11~482
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=204c2bc9cb50daf4d3c8b5067a57c071ef55dfc4;p=strace

Implement RVAL_DECODED flag

Implement a method for "on entering" parsers to return
"done with decoding" information to their callers.

If a syscall parser called from trace_syscall_entering returns a value
with RVAL_DECODED bit set, record this value in tcp->sys_func_rval
and use it in trace_syscall_exiting instead of calling the parser on
exiting syscall.

If an ioctl parser returned RVAL_DECODED, this would tell
SYS_FUNC(ioctl) that the decoding is finished but fallback printing of
the ioctl command argument is needed, while e.g. RVAL_DONE+1 would mean
that the decoding is finished and no fallback decoding is needed.

* defs.h (struct tcb): Add sys_func_rval.
(RVAL_DECODED): New macro.
* syscall.c (trace_syscall_entering): Initialize tcp->sys_func_rval
along with setting TCB_INSYSCALL flag.
(trace_syscall_exiting): Use tcp->sys_func_rval instead of calling
tcp->s_ent->sys_func when the former has RVAL_DECODED flag set.
Reset tcp->sys_func_rval along with clearing TCB_INSYSCALL flag.
* ioctl.c (sys_ioctl): Set RVAL_DECODED flag on exiting.
Print ioctl argument iff RVAL_DECODED is set and fallback decoding
is requested.
---

diff --git a/defs.h b/defs.h
index 6fcb5186..29b98efe 100644
--- a/defs.h
+++ b/defs.h
@@ -274,6 +274,7 @@ struct tcb {
 #if SUPPORTED_PERSONALITIES > 1
 	unsigned int currpers;	/* Personality at the time of scno update */
 #endif
+	int sys_func_rval;	/* Syscall entry parser's return value */
 	int curcol;		/* Output column for this process */
 	FILE *outf;		/* Output file for this process */
 	const char *auxstr;	/* Auxiliary info from syscall (see RVAL_STR) */
@@ -368,6 +369,8 @@ extern const struct xlat whence_codes[];
 #define RVAL_STR	020	/* Print `auxstr' field after return val */
 #define RVAL_NONE	040	/* Print nothing */
 
+#define RVAL_DECODED	0100	/* syscall decoding finished */
+
 #define TRACE_FILE	001	/* Trace file-related syscalls. */
 #define TRACE_IPC	002	/* Trace IPC-related syscalls. */
 #define TRACE_NETWORK	004	/* Trace network-related syscalls. */
diff --git a/ioctl.c b/ioctl.c
index d10e45d2..284828a5 100644
--- a/ioctl.c
+++ b/ioctl.c
@@ -272,6 +272,7 @@ ioctl_decode(struct tcb *tcp)
 SYS_FUNC(ioctl)
 {
 	const struct_ioctlent *iop;
+	int ret;
 
 	if (entering(tcp)) {
 		printfd(tcp, tcp->u_arg[0]);
@@ -286,14 +287,22 @@ SYS_FUNC(ioctl)
 				ioctl_print_code(tcp->u_arg[1]);
 			}
 		}
-		ioctl_decode(tcp);
+		ret = ioctl_decode(tcp);
+	} else {
+		ret = ioctl_decode(tcp) | RVAL_DECODED;
 	}
-	else {
-		int ret = ioctl_decode(tcp);
-		if (!ret)
-			tprintf(", %#lx", tcp->u_arg[2]);
+
+	if (ret & RVAL_DECODED) {
+		ret &= ~RVAL_DECODED;
+		if (ret)
+			--ret;
 		else
-			return ret - 1;
+			tprintf(", %#lx", tcp->u_arg[2]);
+		ret |= RVAL_DECODED;
+	} else {
+		if (ret)
+			--ret;
 	}
-	return 0;
+
+	return ret;
 }
diff --git a/syscall.c b/syscall.c
index 0ab424c1..ea74e353 100644
--- a/syscall.c
+++ b/syscall.c
@@ -814,6 +814,7 @@ trace_syscall_entering(struct tcb *tcp)
 	 || (tracing_paths && !pathtrace_match(tcp))
 	) {
 		tcp->flags |= TCB_INSYSCALL | TCB_FILTERED;
+		tcp->sys_func_rval = 0;
 		return 0;
 	}
 
@@ -844,6 +845,7 @@ trace_syscall_entering(struct tcb *tcp)
 	fflush(tcp->outf);
  ret:
 	tcp->flags |= TCB_INSYSCALL;
+	tcp->sys_func_rval = res;
 	/* Measure the entrance time as late as possible to avoid errors. */
 	if (Tflag || cflag)
 		gettimeofday(&tcp->etime, NULL);
@@ -910,6 +912,7 @@ trace_syscall_exiting(struct tcb *tcp)
 		tprints("= ? <unavailable>\n");
 		line_ended();
 		tcp->flags &= ~TCB_INSYSCALL;
+		tcp->sys_func_rval = 0;
 		return res;
 	}
 	tcp->s_prev_ent = tcp->s_ent;
@@ -928,7 +931,10 @@ trace_syscall_exiting(struct tcb *tcp)
 	 */
 		if (not_failing_only && tcp->u_error)
 			goto ret;	/* ignore failed syscalls */
-		sys_res = tcp->s_ent->sys_func(tcp);
+		if (tcp->sys_func_rval & RVAL_DECODED)
+			sys_res = tcp->sys_func_rval;
+		else
+			sys_res = tcp->s_ent->sys_func(tcp);
 	}
 
 	tprints(") ");
@@ -1081,6 +1087,7 @@ trace_syscall_exiting(struct tcb *tcp)
 
  ret:
 	tcp->flags &= ~TCB_INSYSCALL;
+	tcp->sys_func_rval = 0;
 	return 0;
 }