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authorReinhard Tartler <siretart@tauware.de>2011-10-10 17:43:39 +0200
committerReinhard Tartler <siretart@tauware.de>2011-10-10 17:43:39 +0200
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+.\" $Xorg: README,v 1.3 2000/08/17 19:55:19 cpqbld Exp $
+
+This library replaces the C library allocator;
+providing malloc, free, realloc and calloc (sorry, no valloc)
+
+In doing so, it provides extensive memory bug checking, locating:
+
+ Lost memory; memory which has not been freed and which has no
+ references
+
+ In use free memory; memorhy which has been freed and still has
+ references to it.
+
+ Stores to freed memory
+
+ free/realloc with invalid pointers -- if you pass in a pointer to
+ the middle of an allocated block, it will even tell you which one
+
+For each of these errors, a report entry is generated which includes
+the stack backtrace of either the allocation or free (which ever occured
+last) along with the current stack, when relevant.
+
+Unreferenced allocated memory, stores to freed memory and referenced freed
+memory are only caught when CheckMemory is called. It is automatically
+called each time 1m of data has been freed, and is called when the program
+exits (by registering with atexit(3)/on_exit(3)). You can call it whenever
+you want.
+
+Both the X server and font servers call CheckMemory after each reset when
+their respective os/utils.c are compiled -DMEMBUG.
+
+There are a few global variables you can set with the debugger to
+help isolate problems:
+
+ FindLeakWarnMiddlePointers
+ Normally, memleak ignores pointers to the middle of
+ freed memory. These are frequently simply random data
+ which happens to look like a pointer. Turning this
+ on will generate additional messages.
+ FindLeakAllocBreakpoint
+ At each allocation, memleak increments a serial number
+ and stores it in the allocation header. By rerunning
+ the program, you can stop when that piece of memory
+ is going to be allocated. Store the serial number
+ in this global variable and put a debugger breakpoint inside
+ AddActiveBlock at the indicated line.
+ FindLeakFreeBreakpoint
+ Similarly for freeing memory.
+ FindLeakTime
+ The current serial number
+ FindLeakCheckAlways
+ When set, memleak checks the entire memory system after
+ each allocation or free. This is very expensive, but
+ may catch errors not otherwise found until too late.
+
+To include this in your application, simply place libmemleak.a before the
+end of the link line; it will then override the C library allocator.
+
+To port this system to a new machine, you must provide two values, one
+indicating the lowest data address in a program and one indicating the
+highest stack address. In addition, to get return stack traces (which are
+almost essential for debugging), you must provide the function
+getReturnStack. Samples for MIPS and SPARC are included already.
+
+The output from the leak tracer includes only PC values in the stack
+traces. To convert these into useful values, run the output of
+the leak tracer through the find-routines script; after making sure you have
+built the modified version of gdb-4.4 on your machine.
+
+-keith