kern/164724: Signal bug in Dtrace
Pedro Giffuni
giffunip at tutopia.com
Fri Feb 3 02:10:13 UTC 2012
>Number: 164724
>Category: kern
>Synopsis: Signal bug in Dtrace
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: change-request
>Submitter-Id: current-users
>Arrival-Date: Fri Feb 03 02:10:12 UTC 2012
>Closed-Date:
>Last-Modified:
>Originator: Pedro Giffuni
>Release: 9.0-release
>Organization:
>Environment:
FreeBSD pcbsd-8714 9.0-RELEASE FreeBSD 9.0-RELEASE #3: Tue Dec 27 14:14:29 PST 2011 root at build9x64.pcbsd.org:/usr/obj/builds/amd64/pcbsd-build90/fbsd-source/9.0/sys/GENERIC amd64
>Description:
Last year Bryan Cantrill found a nasty bug in Dtrace:
http://dtrace.org/blogs/bmc/2011/03/09/when-magic-collides/
He warns "you are not expected to understand this", and not
really being used to Dtrace I haven't really reproduced it.
The fix, however, was relatively easy so I adapted the patch
here:
http://dtrace.org/resources/bmc/dtrace-signal.patch
to work on FreeBSD's port.
>How-To-Repeat:
>Fix:
Patch attached
Patch attached with submission follows:
Index: cddl/dev/dtrace/i386/dtrace_subr.c
===================================================================
--- cddl/dev/dtrace/i386/dtrace_subr.c (revision 230923)
+++ cddl/dev/dtrace/i386/dtrace_subr.c (working copy)
@@ -27,6 +27,10 @@
* Use is subject to license terms.
*/
+/*
+ * Copyright (c) 2011, Joyent, Inc. All rights reserved.
+ */
+
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/types.h>
@@ -298,14 +302,15 @@
}
/*
- * If we've executed the original instruction, but haven't performed
- * the jmp back to t->t_dtrace_npc or the clean up of any registers
- * used to emulate %rip-relative instructions in 64-bit mode, do that
- * here and take the signal right away. We detect this condition by
- * seeing if the program counter is the range [scrpc + isz, astpc).
+ * If we have executed the original instruction, but we have performed
+ * neither the jmp back to t->t_dtrace_npc nor the clean up of any
+ * registers used to emulate %rip-relative instructions in 64-bit mode,
+ * we'll save ourselves some effort by doing that here and taking the
+ * signal right away. We detect this condition by seeing if the program
+ * counter is the range [scrpc + isz, astpc).
*/
- if (t->t_dtrace_astpc - rp->r_pc <
- t->t_dtrace_astpc - t->t_dtrace_scrpc - isz) {
+ if (rp->r_pc >= t->t_dtrace_scrpc + isz &&
+ rp->r_pc < t->t_dtrace_astpc) {
#ifdef __amd64
/*
* If there is a scratch register and we're on the
Index: cddl/dev/dtrace/amd64/dtrace_subr.c
===================================================================
--- cddl/dev/dtrace/amd64/dtrace_subr.c (revision 230923)
+++ cddl/dev/dtrace/amd64/dtrace_subr.c (working copy)
@@ -27,6 +27,10 @@
* Use is subject to license terms.
*/
+/*
+ * Copyright (c) 2011, Joyent, Inc. All rights reserved.
+ */
+
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/types.h>
@@ -297,14 +301,15 @@
}
/*
- * If we've executed the original instruction, but haven't performed
- * the jmp back to t->t_dtrace_npc or the clean up of any registers
- * used to emulate %rip-relative instructions in 64-bit mode, do that
- * here and take the signal right away. We detect this condition by
- * seeing if the program counter is the range [scrpc + isz, astpc).
+ * If we have executed the original instruction, but we have performed
+ * neither the jmp back to t->t_dtrace_npc nor the clean up of any
+ * registers used to emulate %rip-relative instructions in 64-bit mode,
+ * we'll save ourselves some effort by doing that here and taking the
+ * signal right away. We detect this condition by seeing if the program
+ * counter is the range [scrpc + isz, astpc).
*/
- if (t->t_dtrace_astpc - rp->r_pc <
- t->t_dtrace_astpc - t->t_dtrace_scrpc - isz) {
+ if (rp->r_pc >= t->t_dtrace_scrpc + isz &&
+ rp->r_pc < t->t_dtrace_astpc) {
#ifdef __amd64
/*
* If there is a scratch register and we're on the
>Release-Note:
>Audit-Trail:
>Unformatted:
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