Grok async contexts. When a thread is interrupted and an upcall

happens, the context of the interrupted thread is exported to
userland. Unlike most contexts, it will be an async context and
we cannot easily use our existing functions to set such a
context.
To avoid a lot of complexity that may possibly interfere with
the common case, we simply let the kernel deal with it. However,
we don't use the EPC based syscall path to invoke setcontext(2).
No, we use the break-based syscall path. That way the trapframe
will be compatible with the context we're trying to restore and
we save the kernel a lot of trouble. The kind of trouble we did
not want to go though ourselves...

However, we also need to set the threads mailbox and there's no
syscall to help us out. To avoid creating a new syscall, we use
the context itself to pass the information to the kernel so that
the kernel can update the mailbox. This involves setting a flag
(_MC_FLAGS_KSE_SET_MBOX) and setting ifa (the address) and isr
(the value).

2 files changed, 41 insertions, 9 deletions

diff --git a/lib/libkse/arch/ia64/ia64/context.S b/lib/libkse/arch/ia64/ia64/context.S
index 6c0c082..49fe42e 100644
--- a/lib/libkse/arch/ia64/ia64/context.S
+++ b/lib/libkse/arch/ia64/ia64/context.S
@@ -27,6 +27,8 @@
 #include <machine/asm.h>
 __FBSDID("$FreeBSD$");
 
+#include <sys/syscall.h>
+
 #define	SIZEOF_SPECIAL	(18*8)
 
 /*
@@ -335,3 +337,15 @@ ENTRY(_ia64_save_context, 1)
 	;;
 }
 END(_ia64_save_context)
+
+/*
+ * void _ia64_break_setcontext(ucontext_t *ucp);
+ */
+ENTRY(_ia64_break_setcontext, 1)
+{	.mib
+	mov		r15=SYS_setcontext
+	break		0x100000
+	br.ret.sptk	rp
+	;;
+}
+END(_ia64_break_setcontext)
diff --git a/lib/libkse/arch/ia64/include/pthread_md.h b/lib/libkse/arch/ia64/include/pthread_md.h
index d6aa130..95f1d2d 100644
--- a/lib/libkse/arch/ia64/include/pthread_md.h
+++ b/lib/libkse/arch/ia64/include/pthread_md.h
@@ -34,8 +34,14 @@
 #include <ucontext.h>
 
 #define	THR_GETCONTEXT(ucp)	_ia64_save_context(&(ucp)->uc_mcontext)
-#define	THR_SETCONTEXT(ucp)	_ia64_restore_context(&(ucp)->uc_mcontext, \
-				    0, NULL)
+#define	THR_SETCONTEXT(ucp)	\
+	do {								\
+		if ((ucp)->uc_mcontext.mc_flags & _MC_FLAGS_ASYNC_CONTEXT) \
+			_ia64_break_setcontext(ucp);			\
+		else							\
+			_ia64_restore_context(&(ucp)->uc_mcontext, 0,	\
+			    NULL);					\
+	} while (0)
 
 #define	PER_THREAD
 
@@ -194,6 +200,7 @@ _get_curkse(void)
 	return (_tcb->tcb_curkcb->kcb_kse);
 }
 
+void _ia64_break_setcontext(ucontext_t *ucp);
 void _ia64_enter_uts(kse_func_t uts, struct kse_mailbox *km, void *stack,
     size_t stacksz);
 int _ia64_restore_context(mcontext_t *mc, intptr_t val, intptr_t *loc);
@@ -218,14 +225,25 @@ _thread_enter_uts(struct tcb *tcb, struct kcb *kcb)
 static __inline int
 _thread_switch(struct kcb *kcb, struct tcb *tcb, int setmbox)
 {
+	mcontext_t *mc;
+
 	_tcb_set(kcb, tcb);
-	if (setmbox != 0)
-		_ia64_restore_context(&tcb->tcb_tmbx.tm_context.uc_mcontext,
-		    (intptr_t)&tcb->tcb_tmbx,
-		    (intptr_t *)&kcb->kcb_kmbx.km_curthread);
-	else
-		_ia64_restore_context(&tcb->tcb_tmbx.tm_context.uc_mcontext,
-		    0, NULL);
+	mc = &tcb->tcb_tmbx.tm_context.uc_mcontext;
+	if (mc->mc_flags & _MC_FLAGS_ASYNC_CONTEXT) {
+		if (setmbox) {
+			mc->mc_flags |= _MC_FLAGS_KSE_SET_MBOX;
+			mc->mc_special.ifa =
+			    (intptr_t)&kcb->kcb_kmbx.km_curthread;
+			mc->mc_special.isr = (intptr_t)&tcb->tcb_tmbx;
+		}
+		_ia64_break_setcontext(&tcb->tcb_tmbx.tm_context);
+	} else {
+		if (setmbox)
+			_ia64_restore_context(mc, (intptr_t)&tcb->tcb_tmbx,
+			    (intptr_t *)&kcb->kcb_kmbx.km_curthread);
+		else
+			_ia64_restore_context(mc, 0, NULL);
+	}
 	/* We should not reach here. */
 	return (-1);
 }