arm: Unbreak debugging programs that use FP instructions

Contrary to arm64, on armv7 get_vfpcontext/set_vfpcontext can be called
from cpu_ptrace. This can be triggered when gdb hits a breakpoint
in a userspace program.
Relax td == currthread assertion to account for that situation.
While here update an outdated comment in vfp_discard.

Reported by: Mark Millard <marklmi@yahoo.com>
Tested by: Mark Millard <marklmi@yahoo.com>
Differential Revision: https://reviews.freebsd.org/D38696

2 files changed, 6 insertions, 13 deletions

diff --git a/sys/arm/arm/exec_machdep.c b/sys/arm/arm/exec_machdep.c
index c14bd51146ef..96b382c9083f 100644
--- a/sys/arm/arm/exec_machdep.c
+++ b/sys/arm/arm/exec_machdep.c
@@ -100,19 +100,18 @@ get_vfpcontext(struct thread *td, mcontext_vfp_t *vfp)
 {
 	struct pcb *pcb;
 
-	MPASS(td == curthread);
+	MPASS(td == curthread || TD_IS_SUSPENDED(td) ||
+	    P_SHOULDSTOP(td->td_proc));
 
 	pcb = td->td_pcb;
-	if ((pcb->pcb_fpflags & PCB_FP_STARTED) != 0) {
+	if ((pcb->pcb_fpflags & PCB_FP_STARTED) != 0 && td == curthread) {
 		critical_enter();
 		vfp_store(&pcb->pcb_vfpstate, false);
 		critical_exit();
 	}
 	KASSERT(pcb->pcb_vfpsaved == &pcb->pcb_vfpstate,
 		("Called get_vfpcontext while the kernel is using the VFP"));
-	memcpy(vfp->mcv_reg, pcb->pcb_vfpstate.reg,
-		sizeof(vfp->mcv_reg));
-	vfp->mcv_fpscr = pcb->pcb_vfpstate.fpscr;
+	memcpy(vfp, &pcb->pcb_vfpstate, sizeof(*vfp));
 }
 
 /*
@@ -123,19 +122,15 @@ set_vfpcontext(struct thread *td, mcontext_vfp_t *vfp)
 {
 	struct pcb *pcb;
 
-	MPASS(td == curthread);
-
 	pcb = td->td_pcb;
-	if ((pcb->pcb_fpflags & PCB_FP_STARTED) != 0) {
+	if (td == curthread) {
 		critical_enter();
 		vfp_discard(td);
 		critical_exit();
 	}
 	KASSERT(pcb->pcb_vfpsaved == &pcb->pcb_vfpstate,
 		("Called set_vfpcontext while the kernel is using the VFP"));
-	memcpy(pcb->pcb_vfpstate.reg, vfp->mcv_reg,
-		sizeof(pcb->pcb_vfpstate.reg));
-	pcb->pcb_vfpstate.fpscr = vfp->mcv_fpscr;
+	memcpy(&pcb->pcb_vfpstate, vfp, sizeof(*vfp));
 }
 #endif
 
diff --git a/sys/arm/arm/vfp.c b/sys/arm/arm/vfp.c
index 915d65c1b790..d51c4b6e0618 100644
--- a/sys/arm/arm/vfp.c
+++ b/sys/arm/arm/vfp.c
@@ -334,8 +334,6 @@ vfp_store(struct vfp_state *vfpsave, boolean_t disable_vfp)
  * The current thread is dying.  If the state currently in the hardware belongs
  * to the current thread, set fpcurthread to NULL to indicate that the VFP
  * hardware state does not belong to any thread.  If the VFP is on, turn it off.
- * Called only from cpu_throw(), so we don't have to worry about a context
- * switch here.
  */
 void
 vfp_discard(struct thread *td)