svn commit: r209292 - stable/8/sys/i386/i386

[Konstantin Belousov]

Author: kib
Date: Fri Jun 18 09:34:31 2010
New Revision: 209292
URL: http://svn.freebsd.org/changeset/base/209292

Log:
  MFC r208604:
  Clarify a potential issue in get_fpcontext() use.

Modified:
  stable/8/sys/i386/i386/machdep.c
Directory Properties:
  stable/8/sys/   (props changed)
  stable/8/sys/amd64/include/xen/   (props changed)
  stable/8/sys/cddl/contrib/opensolaris/   (props changed)
  stable/8/sys/contrib/dev/acpica/   (props changed)
  stable/8/sys/contrib/pf/   (props changed)
  stable/8/sys/dev/xen/xenpci/   (props changed)
  stable/8/sys/geom/sched/   (props changed)

Modified: stable/8/sys/i386/i386/machdep.c
==============================================================================
--- stable/8/sys/i386/i386/machdep.c	Fri Jun 18 09:29:08 2010	(r209291)
+++ stable/8/sys/i386/i386/machdep.c	Fri Jun 18 09:34:31 2010	(r209292)
@@ -633,6 +633,13 @@ sendsig(sig_t catcher, ksiginfo_t *ksi, 
 	sf.sf_uc.uc_mcontext.mc_gs = rgs();
 	bcopy(regs, &sf.sf_uc.uc_mcontext.mc_fs, sizeof(*regs));
 	sf.sf_uc.uc_mcontext.mc_len = sizeof(sf.sf_uc.uc_mcontext); /* magic */
+
+	/*
+	 * The get_fpcontext() call must be placed before assignments
+	 * to mc_fsbase and mc_gsbase due to the alignment-override
+	 * code in get_fpcontext() that possibly clobbers 12 bytes of
+	 * mcontext after mc_fpstate.
+	 */
 	get_fpcontext(td, &sf.sf_uc.uc_mcontext);
 	fpstate_drop(td);
 	/*
@@ -3241,6 +3248,13 @@ get_mcontext(struct thread *td, mcontext
 	mcp->mc_esp = tp->tf_esp;
 	mcp->mc_ss = tp->tf_ss;
 	mcp->mc_len = sizeof(*mcp);
+
+	/*
+	 * The get_fpcontext() call must be placed before assignments
+	 * to mc_fsbase and mc_gsbase due to the alignment-override
+	 * code in get_fpcontext() that possibly clobbers 12 bytes of
+	 * mcontext after mc_fpstate.
+	 */
 	get_fpcontext(td, mcp);
 	sdp = &td->td_pcb->pcb_gsd;
 	mcp->mc_fsbase = sdp->sd_hibase << 24 | sdp->sd_lobase;