Export current system call code and argument count for system call entry

and exit events. procfs stop events for system call tracing report these
values (argument count for system call entry and code for system call exit),
but ptrace() does not provide this information. (Note that while the system
call code can be determined in an ABI-specific manner during system call
entry, it is not generally available during system call exit.)

The values are exported via new fields at the end of struct ptrace_lwpinfo
available via PT_LWPINFO.

Reviewed by:	kib
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D3536

2 files changed, 17 insertions, 0 deletions

diff --git a/sys/kern/subr_syscall.c b/sys/kern/subr_syscall.c
index 070ba28..292b942 100644
--- a/sys/kern/subr_syscall.c
+++ b/sys/kern/subr_syscall.c
@@ -85,6 +85,8 @@ syscallenter(struct thread *td, struct syscall_args *sa)
 		STOPEVENT(p, S_SCE, sa->narg);
 		if (p->p_flag & P_TRACED && p->p_stops & S_PT_SCE) {
 			PROC_LOCK(p);
+			td->td_dbg_sc_code = sa->code;
+			td->td_dbg_sc_narg = sa->narg;
 			ptracestop((td), SIGTRAP);
 			PROC_UNLOCK(p);
 		}
@@ -94,6 +96,10 @@ syscallenter(struct thread *td, struct syscall_args *sa)
 			 * debugger modified registers or memory.
 			 */
 			error = (p->p_sysent->sv_fetch_syscall_args)(td, sa);
+			PROC_LOCK(p);
+			td->td_dbg_sc_code = sa->code;
+			td->td_dbg_sc_narg = sa->narg;
+			PROC_UNLOCK(p);
 #ifdef KTRACE
 			if (KTRPOINT(td, KTR_SYSCALL))
 				ktrsyscall(sa->code, sa->narg, sa->args);
diff --git a/sys/kern/sys_process.c b/sys/kern/sys_process.c
index 6610960..eb50acd 100644
--- a/sys/kern/sys_process.c
+++ b/sys/kern/sys_process.c
@@ -97,6 +97,8 @@ struct ptrace_lwpinfo32 {
 	struct siginfo32 pl_siginfo;	/* siginfo for signal */
 	char	pl_tdname[MAXCOMLEN + 1];	/* LWP name. */
 	int	pl_child_pid;		/* New child pid */
+	u_int		pl_syscall_code;
+	u_int		pl_syscall_narg;
 };
 
 #endif
@@ -481,6 +483,8 @@ ptrace_lwpinfo_to32(const struct ptrace_lwpinfo *pl,
 	siginfo_to_siginfo32(&pl->pl_siginfo, &pl32->pl_siginfo);
 	strcpy(pl32->pl_tdname, pl->pl_tdname);
 	pl32->pl_child_pid = pl->pl_child_pid;
+	pl32->pl_syscall_code = pl->pl_syscall_code;
+	pl32->pl_syscall_narg = pl->pl_syscall_narg;
 }
 #endif /* COMPAT_FREEBSD32 */
 
@@ -1211,6 +1215,13 @@ kern_ptrace(struct thread *td, int req, pid_t pid, void *addr, int data)
 		pl->pl_sigmask = td2->td_sigmask;
 		pl->pl_siglist = td2->td_siglist;
 		strcpy(pl->pl_tdname, td2->td_name);
+		if ((td2->td_dbgflags & (TDB_SCE | TDB_SCX)) != 0) {
+			pl->pl_syscall_code = td2->td_dbg_sc_code;
+			pl->pl_syscall_narg = td2->td_dbg_sc_narg;
+		} else {
+			pl->pl_syscall_code = 0;
+			pl->pl_syscall_narg = 0;
+		}
 #ifdef COMPAT_FREEBSD32
 		if (wrap32)
 			ptrace_lwpinfo_to32(pl, pl32);