Re: Why are Lua Modules Only a Runtime Component of the Language?

["Robert G. Jakabosky" <bobby@...>]

On Monday 07, HyperHacker wrote:
> In C/C++ I often find myself wishing I could globally redefine malloc,
> free, new and delete to print debugging info to track down
> memory-related bugs... in Lua you can do this kind of thing as easily
> as shown above!

You can intercept calls to malloc()/free()/etc.., by using the "--wrap" linker 
option (See manpage for ld).

With gcc you can use the following option:
-Wl,--wrap,malloc,--wrap,calloc,--wrap,free,--wrap,realloc,--wrap,strdup,--
wrap,strndup

Then you create wrapper functions like:
void * __wrap_malloc(size_t size) {
  printf("malloc called with %zu\n", size);
  return __real_malloc(size);
}

I have used this trick to log the memory usage of long running services to 
detect memory leaks.  You can pre-append a header structure to all allocations 
to track the memory block size, so the free()/realloc() functions know the 
block size.  This will also work for C++ code since 'new' calls malloc to 
allocate memory for objects.  Also this should intercept alloc calls from 
other libraries too.

Now when I am writing C code I use an allocator function like the one the Lua 
VM uses, since it allows memory usage tracking without wasting memory to track 
the size of each allocated block.

-- 
Robert G. Jakabosky