* defs.h [LINUX] (TCP_FORK_EVENT): New flag.
* defs.h [LINUX] (internal_fork_child): New argument: from_ptrace_event.
* process.c [LINUX] (internal_fork_child): Ditto.
* process.c [LINUX] (internal_fork): If TCP_FORK_EVENT is set, don't
attach to the child using the syscall return value.
Signed-off-by: Jamie Lokier <ja...@shareable.org>
---
defs.h | 5 +++--
process.c | 51 ++++++++++++++++++++++++++++++++++++++++++++-------
2 files changed, 47 insertions(+), 9 deletions(-)
diff --git a/defs.h b/defs.h
index ab69a45..fadbd92 100644
--- a/defs.h
+++ b/defs.h
@@ -403,11 +403,12 @@ struct tcb {
|| defined(POWERPC) || defined(IA64) || defined(HPPA) \
|| defined(SH) || defined(SH64) || defined(S390) || defined(S390X) \
|| defined(ARM) || defined(MIPS) || defined(BFIN) || defined(TILE)
-# define TCB_WAITEXECVE 02000 /* ignore SIGTRAP after exceve */
+# define TCB_WAITEXECVE 02000 /* Ignore SIGTRAP after exceve */
# endif
# define TCB_CLONE_DETACHED 04000 /* CLONE_DETACHED set in creating syscall */
# define TCB_CLONE_THREAD 010000 /* CLONE_THREAD set in creating syscall */
# define TCB_GROUP_EXITING 020000 /* TCB_EXITING was exit_group, not _exit */
+# define TCB_FORK_EVENT 040000 /* Got PTRACE_EVENT_{FORK,VFORK,CLONE} */
# include <sys/syscall.h>
# ifndef __NR_exit_group
# /* Hack: Most headers around are too old to have __NR_exit_group. */
@@ -566,7 +567,7 @@ extern int is_restart_error(struct tcb *);
extern int change_syscall(struct tcb *, int);
#ifdef LINUX
-extern int internal_fork_child(struct tcb *, int);
+extern int internal_fork_child(struct tcb *, int, int);
#endif
extern int internal_fork(struct tcb *);
extern int internal_exec(struct tcb *);
diff --git a/process.c b/process.c
index 645f2c4..e46957d 100644
--- a/process.c
+++ b/process.c
@@ -790,11 +790,16 @@ change_syscall(struct tcb *tcp, int new)
#ifdef LINUX
/*
* Called when we learn about a child process and know which parent
- * it's from. (Dubiously, pid here is int because alloctcb() uses it,
- * but syscall return values are unsigned long and could overflow.)
+ * it's from. (Dubiously, pid here is int
+ * because alloctcb() uses it, but syscall return values are unsigned
+ * long and could overflow.)
+ *
+ * from_ptrace_event is set if called for PTRACE_EVENT_{FORK,VFORK,CLONE}.
+ * Then we know the child is attached and tracing despite CLONE_PTRACE
+ * not being used.
*/
int
-internal_fork_child(struct tcb *tcp, int pid)
+internal_fork_child(struct tcb *tcp, int pid, int from_ptrace_event)
{
struct tcb *tcpchild;
int clone_flags;
@@ -814,6 +819,26 @@ internal_fork_child(struct tcb *tcp, int pid)
tcpchild = alloctcb(pid);
}
+ /* Set by setbpt. */
+ clone_flags = tcp->u_arg[ARG_FLAGS];
+
+ /* This handles the cases when we didn't use CLONE_PTRACE
+ because we requested PTRACE_EVENT_{FORK,VFORK,CLONE}, but
+ for some reason we didn't get the event. It's not perfect
+ because the child isn't stopped immediately. This should
+ never happen, but it's easy and there have been kernel
+ bugs, so let's do it. */
+ if (!from_ptrace_event && !(clone_flags & CLONE_PTRACE)) {
+ /* Linux returns EPERM if the child has exited by now. */
+ if (ptrace(PTRACE_ATTACH, pid, (char *) 1, 0) < 0) {
+ if (tcp->flags & TCB_BPTSET)
+ clearbpt(tcp);
+ perror("PTRACE_ATTACH");
+ fprintf(stderr, "Too late?\n");
+ droptcb(tcpchild);
+ return 0;
+ }
+ }
tcpchild->flags |= TCB_ATTACHED;
if ((tcp->flags & TCB_CLONE_THREAD) && tcp->parent != NULL) {
@@ -832,9 +857,6 @@ internal_fork_child(struct tcb *tcp, int pid)
}
++(tcpchild->parent)->nchildren;
- /* Set by setbpt. */
- clone_flags = tcp->u_arg[ARG_FLAGS];
-
if (clone_flags & CLONE_THREAD) {
tcpchild->flags |= TCB_CLONE_THREAD;
++(tcpchild->parent)->nclone_threads;
@@ -902,9 +924,24 @@ internal_fork(struct tcb *tcp)
return 0;
}
+ if (tcp->flags & TCB_FORK_EVENT) {
+ /*
+ * We've begun tracing the child already.
+ * Don't use the syscall return value to attach
+ * to the child, (a) to avoid confusion, (b)
+ * because the child may have been traced,
+ * finished and exited already, and (c) it's
+ * definitely exited if this was a vfork.
+ */
+ tcp->flags &= ~TCB_FORK_EVENT;
+ if (bpt)
+ clearbpt(tcp);
+ return 0;
+ }
+
pid = tcp->u_rval;
- return internal_fork_child(tcp, pid);
+ return internal_fork_child(tcp, pid, 0);
}
return 0;
}
--
1.7.0.4
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