This supports three build modes:
No additional -D options, default legacy mode
-DSUPPORT_DIRECT_MALLOC, magic will use direct calls to libc malloc/free
and will leave in place the symbols now renamed as mallocMagicLegacy()
freeMagicLegacy() and callocMagicLegacy().
-DSUPPORT_DIRECT_MALLOC -DSUPPORT_REMOVE_MALLOC_LEGACY as above but will
remove the three legacy functions from the binary to provide assurance
they can not be used.
The system malloc is thread-safe the legacy magic malloc has a global
deferred free pointer and the mmap() allocate has a free-list that is
not thread-safe making use of free not thread-safe.
This could of course be improved with the use of
atomic_compare_and_exchange operations but for what gain ?
Then there is the additional function call overhead (of the indirection)
and a few tests/branches inserted into a commonly used code paths around
memory allocation, it hides the call site of the malloc/free usage from
the compiler which maybe have special optimization cases.
The existing malloc/free makes static code analysis around memory
allocation more problematic, also use of runtime analysers will operate
better with a fail-fast to bad memory usage.
Darryl L. Miles
f173c0ebda