From 03fb0d95c6c009fdb5d537a7306d0e20651c3a1b Mon Sep 17 00:00:00 2001
From: "Markus F.X.J. Oberhumer" <markus@oberhumer.com>
Date: Tue, 14 Jan 2003 21:41:03 +0000
Subject: [PATCH] Rewrote MemBuffer to do some internal checks.

committer: mfx <mfx> 1042580463 +0000
---
 src/mem.cpp | 101 +++++++++++++++++++++++++++++++---------------------
 src/mem.h   |  15 ++++----
 2 files changed, 66 insertions(+), 50 deletions(-)

diff --git a/src/mem.cpp b/src/mem.cpp
index 764974bc..72b48f90 100644
--- a/src/mem.cpp
+++ b/src/mem.cpp
@@ -35,10 +35,10 @@
 **************************************************************************/
 
 MemBuffer::MemBuffer(unsigned size) :
-    ptr(NULL), alloc_ptr(NULL), alloc_size(0)
+    ptr(NULL), psize(0)
 {
     if (size > 0)
-        alloc(size, 0);
+        alloc(size);
 }
 
 
@@ -49,44 +49,13 @@ MemBuffer::~MemBuffer()
 
 void MemBuffer::dealloc()
 {
-    if (alloc_ptr)
-        ::free(alloc_ptr);
-    alloc_ptr = ptr = NULL;
-    alloc_size = 0;
-}
-
-
-unsigned MemBuffer::getSize() const
-{
-    if (!alloc_ptr)
-        return 0;
-    unsigned size = alloc_size - (ptr - alloc_ptr);
-    assert((int)size > 0);
-    return size;
-}
-
-
-void MemBuffer::alloc(unsigned size, unsigned base_offset)
-{
-    // NOTE: we don't automaticlly free a used buffer
-    assert(alloc_ptr == NULL);
-    assert((int)size > 0);
-    size = base_offset + size;
-    alloc_ptr = (unsigned char *) malloc(size);
-    if (!alloc_ptr)
+    if (ptr)
     {
-        //throw bad_alloc();
-        throwCantPack("out of memory");
-        //exit(1);
+        checkState();
+        ::free(ptr - 8);
     }
-    alloc_size = size;
-    ptr = alloc_ptr + base_offset;
-}
-
-
-void MemBuffer::alloc(unsigned size)
-{
-    alloc(size, 0);
+    ptr = NULL;
+    psize = 0;
 }
 
 
@@ -94,7 +63,7 @@ void MemBuffer::allocForCompression(unsigned uncompressed_size, unsigned extra)
 {
     assert((int)uncompressed_size > 0);
     assert((int)extra >= 0);
-    alloc(uncompressed_size + uncompressed_size/8 + 256 + extra, 0);
+    alloc(uncompressed_size + uncompressed_size/8 + 256 + extra);
 }
 
 
@@ -102,8 +71,58 @@ void MemBuffer::allocForUncompression(unsigned uncompressed_size, unsigned extra
 {
     assert((int)uncompressed_size > 0);
     assert((int)extra >= 0);
-    //alloc(uncompressed_size + 3 + 512 + extra, 0);  // 512 safety bytes
-    alloc(uncompressed_size + 3 + extra, 0);  // 3 bytes for asm_fast decompresion
+    // note: 3 bytes are allowed overrun for the asm_fast decompressors
+//    alloc(uncompressed_size + 3 + 512 + extra); // 512 safety bytes
+    alloc(uncompressed_size + 3 + extra);
+}
+
+
+/*************************************************************************
+//
+**************************************************************************/
+
+#define MAGIC1(p)       ((unsigned)(p) ^ 0xfefdbeeb)
+#define MAGIC2(p)       ((unsigned)(p) ^ 0xfefdbeeb ^ 0x80024001)
+
+unsigned MemBuffer::global_alloc_counter = 0;
+
+
+void MemBuffer::checkState() const
+{
+    if (!ptr)
+        throwInternalError("block not allocated");
+    if (get_be32(ptr - 4) != MAGIC1(ptr))
+        throwInternalError("memory clobbered before allocated block 1");
+    if (get_be32(ptr - 8) != psize)
+        throwInternalError("memory clobbered before allocated block 2");
+    if (get_be32(ptr + psize) != MAGIC2(ptr))
+        throwInternalError("memory clobbered past end of allocated block");
+}
+
+
+void MemBuffer::alloc(unsigned size)
+{
+    // NOTE: we don't automaticlly free a used buffer
+    assert(ptr == NULL);
+    assert(psize == 0);
+    //
+    assert((int)size > 0);
+    unsigned total = 4 + 4 + size + 4 + 4;
+    assert((int)total > 0);
+    unsigned char *p = (unsigned char *) malloc(total);
+    if (!p)
+    {
+        //throw bad_alloc();
+        throwCantPack("out of memory");
+        //exit(1);
+    }
+    ptr = p + 8;
+    psize = size;
+    // store magic state
+    set_be32(ptr - 8, psize);
+    set_be32(ptr - 4, MAGIC1(ptr));
+    set_be32(ptr + psize, MAGIC2(ptr));
+    set_be32(ptr + psize + 4, global_alloc_counter++);
 }
 
 
diff --git a/src/mem.h b/src/mem.h
index dd6d1b87..c6e8d2d0 100644
--- a/src/mem.h
+++ b/src/mem.h
@@ -46,24 +46,21 @@ public:
 
     void dealloc();
 
-    const unsigned char *getBuf()     const { return ptr; }
-    unsigned getSize() const;
+    void checkState() const;
+
+    unsigned getSize() const { return psize; }
 
     operator       unsigned char * ()       { return ptr; }
     //operator const unsigned char * () const { return ptr; }
-
+    const unsigned char *getBuf()     const { return ptr; }
           void *getVoidPtr()                { return (void *) ptr; }
     const void *getVoidPtr() const          { return (const void *) ptr; }
 
 private:
-    void alloc(unsigned size, unsigned base_offset);
-
-protected:
     unsigned char *ptr;
-    unsigned char *alloc_ptr;
-    unsigned alloc_size;
+    unsigned psize;
+    static unsigned global_alloc_counter;
 
-private:
     // disable copy and assignment
     MemBuffer(MemBuffer const &); // {}
     MemBuffer& operator= (MemBuffer const &); // { return *this; }