Xtensa ESP32: Corrects a problem with dispatching to signal handlers: Cannot vector directly to the signal handling function as in other ABIs under the Xtensa Window ABI. In that case, we need to go through a tiny hook when performs the correct window call (call4) otherwise registers will be scrambled in the signal handler

arch/xtensa/src/common/xtensa.h

@@ -317,7 +317,8 @@ void xtensa_coproc_restorestate(struct xtensa_cpstate_s *cpstate);
 
 /* Signals */
 
-void xtensa_sigdeliver(void);
+void _xtensa_sig_trampoline(void);
+void xtensa_sig_deliver(void);
 
 /* Chip-specific functions **************************************************/
 /* Chip specific functions defined in arch/xtensa/src/<chip> */

arch/xtensa/src/common/xtensa_schedsigaction.c

@@ -150,7 +150,7 @@ void up_schedule_sigaction(struct tcb_s *tcb, sig_deliver_t sigdeliver)
                * disabled
                */
 
-              CURRENT_REGS[REG_PC]      = (uint32_t)xtensa_sigdeliver;
+              CURRENT_REGS[REG_PC]      = (uint32_t)_xtensa_sig_trampoline;
 #ifdef __XTENSA_CALL0_ABI__
               CURRENT_REGS[REG_PS]      = (uint32_t)(PS_INTLEVEL(XCHAL_EXCM_LEVEL) | PS_UM);
 #else
@@ -185,7 +185,7 @@ void up_schedule_sigaction(struct tcb_s *tcb, sig_deliver_t sigdeliver)
            * disabled
            */
 
-          tcb->xcp.regs[REG_PC]      = (uint32_t)xtensa_sigdeliver;
+          tcb->xcp.regs[REG_PC]      = (uint32_t)_xtensa_sig_trampoline;
 #ifdef __XTENSA_CALL0_ABI__
           tcb->xcp.regs[REG_PS]      = (uint32_t)(PS_INTLEVEL(XCHAL_EXCM_LEVEL) | PS_UM);
 #else

arch/xtensa/src/common/xtensa_sigdeliver.c

@@ -58,7 +58,7 @@
  ****************************************************************************/
 
 /****************************************************************************
- * Name: xtensa_sigdeliver
+ * Name: xtensa_sig_deliver
  *
  * Description:
  *   This is the a signal handling trampoline.  When a signal action was
@@ -67,7 +67,7 @@
  *
  ****************************************************************************/
 
-void xtensa_sigdeliver(void)
+void xtensa_sig_deliver(void)
 {
   struct tcb_s  *rtcb = this_task();
   uint32_t regs[XCPTCONTEXT_REGS];

arch/xtensa/src/common/xtensa_sigtramp.S

@@ -0,0 +1,79 @@
+/****************************************************************************
+ * arch/xtensa/src/common/xtensa_sigtramp.S
+ *
+ * Adapted from use in NuttX by:
+ *
+ *   Copyright (C) 2016 Gregory Nutt. All rights reserved.
+ *   Author: Gregory Nutt <gnutt@nuttx.org>
+ *
+ * Derives from logic originally provided by Cadence Design Systems Inc.
+ *
+ *   Copyright (c) 2006-2015 Cadence Design Systems Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included
+ * in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ ****************************************************************************/
+
+	.file	"xtensa_sigtramp.S"
+
+/****************************************************************************
+ * Included Files
+ ****************************************************************************/
+
+#include <nuttx/config.h>
+
+#include "xtensa_abi.h"
+
+/****************************************************************************
+ * Public Functions
+ ****************************************************************************/
+
+/****************************************************************************
+ * Name: _xtensa_sig_trampoline
+ *
+ * Description:
+ *   Just sets up a proper window call to xtensa_sig_deliver().  We get
+ *   here via a context switch setup in up_schedule_signaction.  Which
+ *   re-vectors the context switch to this location.
+ *
+ *   Here we just call xtensa_sig_deliver() using the proper ABI.  NOTE
+ *   that this function cannot return and depends on the fact that
+ *   xtensa_sig_deliver() does not return.
+ *
+ *
+ ****************************************************************************/
+
+	.text
+	.global	_xtensa_sig_trampoline
+	.type	_xtensa_sig_trampoline, @function
+	.align	4
+
+_xtensa_sig_trampoline:
+	ENTRY(16)
+
+#ifdef __XTENSA_CALL0_ABI__
+	cali0	xtensa_sig_deliver				/* Call xtensa_sig_deliver */
+#else
+	call4	xtensa_sig_deliver				/* Call xtensa_sig_deliver */
+#endif
+
+1:	j		1b
+
+	.size	_xtensa_sig_trampoline, . - _xtensa_sig_trampoline

arch/xtensa/src/esp32/Make.defs

@@ -42,6 +42,7 @@ HEAD_CSRC  = esp32_start.c
 # Common XTENSA files (arch/xtensa/src/common)
 
 CMN_ASRCS  = xtensa_context.S xtensa_coproc.S xtensa_cpuint.S xtensa_panic.S
+CMN_ASRCS += xtensa_sigtramp.S
 
 CMN_CSRCS  = xtensa_assert.c xtensa_blocktask.c xtensa_copystate.c
 CMN_CSRCS += xtensa_cpenable.c xtensa_createstack.c xtensa_exit.c xtensa_idle.c

configs/esp32-core/README.txt

@@ -704,12 +704,8 @@ NOTES:
 
     NOTES:
     1. See NOTES for the nsh configuration.
-    2. 2016-12-23: I have only tried to execute this once and I see some
+    2. 2016-12-23: Test appears to be fully functional in the single CPU mode.
-       assertion from like 87 of xtensa_sigdeliver.c:
+       I have not yet tried SMP mode.
-
-       ASSERT(rtcb->xcp.sigdeliver != NULL);
-
-       I have not yet looked into this.
 
 Things to Do
 ============