From 2b04ad72ee2dd9dea9f8259635c1e0e2b6a317aa Mon Sep 17 00:00:00 2001
From: patacongo <patacongo@42af7a65-404d-4744-a932-0658087f49c3>
Date: Fri, 5 Nov 2010 00:29:37 +0000
Subject: [PATCH] Update some comments
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@3073 42af7a65-404d-4744-a932-0658087f49c3
---
arch/avr/include/avr32/irq.h | 1 -
arch/avr/src/avr32/up_fullcontextrestore.S | 22 ++++++++++++++++++++++
arch/avr/src/avr32/up_sigdeliver.c | 17 +++++++++++++++--
3 files changed, 37 insertions(+), 3 deletions(-)
diff --git a/arch/avr/include/avr32/irq.h b/arch/avr/include/avr32/irq.h
index caa6e9f5a9..a9d0d86264 100644
--- a/arch/avr/include/avr32/irq.h
+++ b/arch/avr/include/avr32/irq.h
@@ -98,7 +98,6 @@
#define INTCONTEXT_REGS 8 /* r8-r12, lr, pc, sr */
#define XCPTCONTEXT_REGS 17 /* Plus r0-r7, sp */
-
/****************************************************************************
* Public Types
****************************************************************************/
diff --git a/arch/avr/src/avr32/up_fullcontextrestore.S b/arch/avr/src/avr32/up_fullcontextrestore.S
index c402393074..c883c58c7e 100755
--- a/arch/avr/src/avr32/up_fullcontextrestore.S
+++ b/arch/avr/src/avr32/up_fullcontextrestore.S
@@ -53,6 +53,28 @@
/****************************************************************************
* Name: up_fullcontextrestore
*
+ * Descripion:
+ * Restore the full-running contex of a thread.
+ *
+ * NOTE: Thus function must handle one very strange case. That is when
+ * this function is called with up_sigdeliver(). That case is strange in
+ * two ways:
+ *
+ * 1. It is not a context switch between threads. Rather, up_fullcontextrestore
+ * must behave more it more like a longjmp within the same task, using the
+ * same stack.
+ * 2. In this case, this function is called with r12 pointing to a register
+ * save area on the stack to be destroyed. This is dangerous for two
+ * reasons: (a) there is a period of time where the stack contents still
+ * contain valid data, but are outside of range protected by the stack
+ * pointer (hence, interrupts must be disabled), and (b) there is the
+ * very real possibility that the new stack pointer might overlap with
+ * the register save area and stack usage in this function might corrupt
+ * the register save data before the state is restored.
+ *
+ * Input Parameters:
+ * r12 = A pointer to the register save area of the thread to be restored.
+ *
* C Prototype:
* void up_fullcontextrestore(uint32_t *regs);
*
diff --git a/arch/avr/src/avr32/up_sigdeliver.c b/arch/avr/src/avr32/up_sigdeliver.c
index aa3940b798..b000f118a8 100644
--- a/arch/avr/src/avr32/up_sigdeliver.c
+++ b/arch/avr/src/avr32/up_sigdeliver.c
@@ -82,7 +82,7 @@
void up_sigdeliver(void)
{
_TCB *rtcb = (_TCB*)g_readytorun.head;
- uint32_t regs[XCPTCONTEXT_REGS];
+ uint32_t regs[XCPTCONTEXT_REGS+3]; /* Why +3? See below */
sig_deliver_t sigdeliver;
/* Save the errno. This must be preserved throughout the signal handling
@@ -128,7 +128,20 @@ void up_sigdeliver(void)
(void)irqsave();
rtcb->pterrno = saved_errno;
- /* Then restore the correct state for this thread of execution. */
+ /* Then restore the correct state for this thread of execution. This is an
+ * unusual case that must be handled by up_fullcontextresore. This case is
+ * unusal in two ways:
+ *
+ * 1. It is not a context switch between threads. Rather, up_fullcontextrestore
+ * must behave more it more like a longjmp within the same task, using
+ * he same stack.
+ * 2. In this case, up_fullcontextrestore is called with r12 pointing to
+ * a register save area on the stack to be destroyed. This is
+ * dangerous because there is the very real possibility that the new
+ * stack pointer might overlap with the register save area and hat stack
+ * usage in up_fullcontextrestore might corrupt the register save data
+ * before the state is restored.
+ */
up_ledoff(LED_SIGNAL);
up_fullcontextrestore(regs);
--
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