Add helper functions to clear/restore syserror

* defs.h (temporarily_clear_syserror, restore_cleared_syserror):
New prototypes.
* syscall.c (saved_u_error): New variable.
(temporarily_clear_syserror, restore_cleared_syserror): New functions.
* aio.c (sys_io_getevents): Use temporarily_clear_syserror
and restore_cleared_syserror.
* mq.c (sys_mq_timedreceive): Likewise.
* signal.c (sys_rt_sigtimedwait): Likewise.

Author: ldv-alt

aio.c

@@ -244,7 +244,14 @@ SYS_FUNC(io_getevents)
 			tprints("], ");
 		}
 
+		/*
+		 * Since the timeout parameter is read by the kernel
+		 * on entering syscall, it has to be decoded the same way
+		 * whether the syscall has failed or not.
+		 */
+		temporarily_clear_syserror(tcp);
 		print_timespec(tcp, tcp->u_arg[4]);
+		restore_cleared_syserror(tcp);
 	}
 	return 0;
 }

defs.h

@@ -538,6 +538,9 @@ extern void get_regs(pid_t pid);
 extern int get_scno(struct tcb *tcp);
 extern const char *syscall_name(long scno);
 
+extern void temporarily_clear_syserror(struct tcb *);
+extern void restore_cleared_syserror(struct tcb *);
+
 extern int umoven(struct tcb *, long, unsigned int, void *);
 #define umove(pid, addr, objp)	\
 	umoven((pid), (addr), sizeof(*(objp)), (void *) (objp))

mq.c

@@ -59,7 +59,14 @@ SYS_FUNC(mq_timedreceive)
 	else {
 		printstr(tcp, tcp->u_arg[1], tcp->u_arg[2]);
 		tprintf(", %lu, %ld, ", tcp->u_arg[2], tcp->u_arg[3]);
+		/*
+		 * Since the timeout parameter is read by the kernel
+		 * on entering syscall, it has to be decoded the same way
+		 * whether the syscall has failed or not.
+		 */
+		temporarily_clear_syserror(tcp);
 		printtv(tcp, tcp->u_arg[4]);
+		restore_cleared_syserror(tcp);
 	}
 	return 0;
 }

signal.c

@@ -673,7 +673,16 @@ SYS_FUNC(rt_sigtimedwait)
 		/* syscall exit, and u_arg[1] was NULL */
 		return 0;
 	}
+
+	/*
+	 * Since the timeout parameter is read by the kernel
+	 * on entering syscall, it has to be decoded the same way
+	 * whether the syscall has failed or not.
+	 */
+	temporarily_clear_syserror(tcp);
 	print_timespec(tcp, tcp->u_arg[2]);
+	restore_cleared_syserror(tcp);
+
 	tprintf(", %lu", tcp->u_arg[3]);
 	return 0;
 };

syscall.c

@@ -1131,6 +1131,21 @@ trace_syscall(struct tcb *tcp)
 		trace_syscall_exiting(tcp) : trace_syscall_entering(tcp);
 }
 
+static int saved_u_error;
+
+void
+temporarily_clear_syserror(struct tcb *tcp)
+{
+	saved_u_error = tcp->u_error;
+	tcp->u_error = 0;
+}
+
+void
+restore_cleared_syserror(struct tcb *tcp)
+{
+	tcp->u_error = saved_u_error;
+}
+
 /*
  * Cannot rely on __kernel_[u]long_t being defined,
  * it is quite a recent feature of <asm/posix_types.h>.