added memcheck library

git-svn-id: https://arducopter.googlecode.com/svn/trunk@3206 f9c3cf11-9bcb-44bc-f272-b75c42450872

libraries/memcheck/memcheck.cpp

@@ -0,0 +1,62 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+
+/*
+  note that we use a 32 bit sentinal to reduce the chance
+  of false positives with uninitialised stack variables
+ */
+
+#include <AP_Common.h>
+
+static const uint32_t *stack_low;
+extern unsigned __brkval;
+
+#define STACK_OFFSET 2
+#define SENTINAL 0x28021967
+
+/*
+  return the current stack pointer
+ */
+static __attribute__((noinline)) const uint32_t *current_stackptr(void) 
+{
+    return (const uint32_t *)__builtin_frame_address(0);
+}
+
+/*
+  this can be added in deeply nested code to ensure we catch 
+  deep stack usage. It should be caught by the sentinal, but this
+  is an added protection
+ */
+void memcheck_update_stackptr(void)
+{
+    if (current_stackptr() < stack_low) {
+        unsigned s = (unsigned)(current_stackptr() - STACK_OFFSET);
+        stack_low = (uint32_t *)(s & ~3);
+    }
+}
+
+/*
+  initialise memcheck, setting up the sentinals
+ */
+void memcheck_init(void)
+{
+    uint32_t *p;
+    free(malloc(1)); // ensure heap is initialised
+    stack_low = current_stackptr();
+    memcheck_update_stackptr();
+    for (p=(uint32_t *)(stack_low-1); p>(uint32_t *)__brkval; p--) {
+        *p = SENTINAL;
+    }
+}
+
+/*
+  this returns the real amount of free memory by looking for
+  overwrites of the stack sentinal values
+ */
+unsigned memcheck_available_memory(void)
+{
+    memcheck_update_stackptr();
+    while (*stack_low != SENTINAL && stack_low > (const uint32_t *)__brkval) {
+        stack_low--;
+    }
+    return (unsigned)(stack_low) - __brkval;
+}

libraries/memcheck/memcheck.h

@@ -0,0 +1,6 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+
+unsigned memcheck_available_memory(void);
+void memcheck_init(void);
+void memcheck_update_stackptr(void);
+