svn commit: r257670 - head/lib/libproc

[Mark Johnston]

Author: markj
Date: Tue Nov  5 03:23:54 2013
New Revision: 257670
URL: http://svnweb.freebsd.org/changeset/base/257670

Log:
  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.
  
  Reported by:	symbolics at gmx.com
  Reviewed by:	rpaulo
  MFC after:	1 month

Modified:
  head/lib/libproc/proc_bkpt.c

Modified: head/lib/libproc/proc_bkpt.c
==============================================================================
--- head/lib/libproc/proc_bkpt.c	Tue Nov  5 02:57:34 2013	(r257669)
+++ head/lib/libproc/proc_bkpt.c	Tue Nov  5 03:23:54 2013	(r257670)
@@ -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, u
 		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, u
 	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, u
 	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, u
 {
 	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, u
 	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);
 }
 
 /*