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

4 files changed, 22 insertions, 1 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);
diff --git a/sys/sys/proc.h b/sys/sys/proc.h
index 62c4b05..ae01bbf 100644
--- a/sys/sys/proc.h
+++ b/sys/sys/proc.h
@@ -174,6 +174,7 @@ struct procdesc;
 struct racct;
 struct sbuf;
 struct sleepqueue;
+struct syscall_args;
 struct td_sched;
 struct thread;
 struct trapframe;
@@ -282,6 +283,8 @@ struct thread {
 	int		td_no_sleeping;	/* (k) Sleeping disabled count. */
 	int		td_dom_rr_idx;	/* (k) RR Numa domain selection. */
 	void		*td_su;		/* (k) FFS SU private */
+	u_int		td_dbg_sc_code;	/* (c) Syscall code to debugger. */
+	u_int		td_dbg_sc_narg;	/* (c) Syscall arg count to debugger.*/
 #define	td_endzero td_sigmask
 
 /* Copied during fork1() or create_thread(). */
@@ -979,7 +982,6 @@ void	userret(struct thread *, struct trapframe *);
 
 void	cpu_exit(struct thread *);
 void	exit1(struct thread *, int, int) __dead2;
-struct syscall_args;
 int	cpu_fetch_syscall_args(struct thread *td, struct syscall_args *sa);
 void	cpu_fork(struct thread *, struct proc *, struct thread *, int);
 void	cpu_set_fork_handler(struct thread *, void (*)(void *), void *);
diff --git a/sys/sys/ptrace.h b/sys/sys/ptrace.h
index e770a06..de4e7a7 100644
--- a/sys/sys/ptrace.h
+++ b/sys/sys/ptrace.h
@@ -113,6 +113,8 @@ struct ptrace_lwpinfo {
 	struct __siginfo 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;
 };
 
 /* Argument structure for PT_VM_ENTRY. */