MFC r257670:

Modify the libproc breakpoint add/remove functions to stop the target
process if it has not already been stopped, since this is required for
ptrace(2) to work.

libdtrace does not seem to stop target processes before trying to remove
their breakpoints, so we were previously failing to remove the breakpoint
on r_debug_state() in rtld. This was causing processes to die with SIGTRAP
if they called dlopen(3) after dtrace(1) had detached.

1 files changed, 59 insertions, 7 deletions

diff --git a/lib/libproc/proc_bkpt.c b/lib/libproc/proc_bkpt.c
index 1878c7f..2c2761a 100644
--- a/lib/libproc/proc_bkpt.c
+++ b/lib/libproc/proc_bkpt.c
@@ -37,8 +37,9 @@ __FBSDID("$FreeBSD$");
 
 #include <assert.h>
 #include <err.h>
-#include <stdio.h>
 #include <errno.h>
+#include <signal.h>
+#include <stdio.h>
 #include "_libproc.h"
 
 #if defined(__i386__) || defined(__amd64__)
@@ -54,12 +55,39 @@ __FBSDID("$FreeBSD$");
 #error "Add support for your architecture"
 #endif
 
+static void
+proc_cont(struct proc_handle *phdl)
+{
+
+	ptrace(PT_CONTINUE, proc_getpid(phdl), (caddr_t)1, 0);
+}
+
+static int
+proc_stop(struct proc_handle *phdl)
+{
+	int status;
+
+	if (kill(proc_getpid(phdl), SIGSTOP) == -1) {
+		DPRINTF("kill %d", proc_getpid(phdl));
+		return (-1);
+	} else if (waitpid(proc_getpid(phdl), &status, WSTOPPED) == -1) {
+		DPRINTF("waitpid %d", proc_getpid(phdl));
+		return (-1);
+	} else if (!WIFSTOPPED(status)) {
+		DPRINTFX("waitpid: unexpected status 0x%x", status);
+		return (-1);
+	}
+
+	return (0);
+}
+
 int
 proc_bkptset(struct proc_handle *phdl, uintptr_t address,
     unsigned long *saved)
 {
 	struct ptrace_io_desc piod;
 	unsigned long paddr, caddr;
+	int ret = 0;
 
 	*saved = 0;
 	if (phdl->status == PS_DEAD || phdl->status == PS_UNDEAD ||
@@ -68,6 +96,12 @@ proc_bkptset(struct proc_handle *phdl, uintptr_t address,
 		return (-1);
 	}
 
+	DPRINTFX("adding breakpoint at 0x%lx", address);
+
+	if (phdl->status != PS_STOP)
+		if (proc_stop(phdl) != 0)
+			return (-1);
+
 	/*
 	 * Read the original instruction.
 	 */
@@ -80,7 +114,8 @@ proc_bkptset(struct proc_handle *phdl, uintptr_t address,
 	if (ptrace(PT_IO, proc_getpid(phdl), (caddr_t)&piod, 0) < 0) {
 		DPRINTF("ERROR: couldn't read instruction at address 0x%"
 		    PRIuPTR, address);
-		return (-1);
+		ret = -1;
+		goto done;
 	}
 	*saved = paddr;
 	/*
@@ -95,10 +130,16 @@ proc_bkptset(struct proc_handle *phdl, uintptr_t address,
 	if (ptrace(PT_IO, proc_getpid(phdl), (caddr_t)&piod, 0) < 0) {
 		DPRINTF("ERROR: couldn't write instruction at address 0x%"
 		    PRIuPTR, address);
-		return (-1);
+		ret = -1;
+		goto done;
 	}
 
-	return (0);
+done:
+	if (phdl->status != PS_STOP)
+		/* Restart the process if we had to stop it. */
+		proc_cont(phdl);
+
+	return (ret);
 }
 
 int
@@ -107,13 +148,20 @@ proc_bkptdel(struct proc_handle *phdl, uintptr_t address,
 {
 	struct ptrace_io_desc piod;
 	unsigned long paddr, caddr;
+	int ret = 0;
 
 	if (phdl->status == PS_DEAD || phdl->status == PS_UNDEAD ||
 	    phdl->status == PS_IDLE) {
 		errno = ENOENT;
 		return (-1);
 	}
-	DPRINTFX("removing breakpoint at 0x%lx\n", address);
+
+	DPRINTFX("removing breakpoint at 0x%lx", address);
+
+	if (phdl->status != PS_STOP)
+		if (proc_stop(phdl) != 0)
+			return (-1);
+
 	/*
 	 * Overwrite the breakpoint instruction that we setup previously.
 	 */
@@ -126,10 +174,14 @@ proc_bkptdel(struct proc_handle *phdl, uintptr_t address,
 	if (ptrace(PT_IO, proc_getpid(phdl), (caddr_t)&piod, 0) < 0) {
 		DPRINTF("ERROR: couldn't write instruction at address 0x%"
 		    PRIuPTR, address);
-		return (-1);
+		ret = -1;
 	}
+
+	if (phdl->status != PS_STOP)
+		/* Restart the process if we had to stop it. */
+		proc_cont(phdl);
  
-	return (0);
+	return (ret);
 }
 
 /*