sudo-baron-samedit-9.cpp

//glibc_2.17-322.el7_9/malloc/malloc.c
/* Set size/use field */
#define set_head(p, s)       ((p)->size = (s))

static void*
_int_malloc(mstate av, size_t bytes)
{
    ...
  use_top:
    /*
      If large enough, split off the chunk bordering the end of memory
      (held in av->top). Note that this is in accord with the best-fit
      search rule.  In effect, av->top is treated as larger (and thus
      less well fitting) than any other available chunk since it can
      be extended to be as large as necessary (up to system
      limitations).

      We require that av->top always exists (i.e., has size >=
      MINSIZE) after initialization, so if it would otherwise be
      exhausted by current request, it is replenished. (The main
      reason for ensuring it exists is that we may need MINSIZE space
      to put in fenceposts in sysmalloc.)
    */

    victim = av->top;
    size = chunksize(victim);

    if ((unsigned long)(size) >= (unsigned long)(nb + MINSIZE)) {
      remainder_size = size - nb;
      remainder = chunk_at_offset(victim, nb);
      av->top = remainder;
      set_head(victim, nb | PREV_INUSE |
               (av != &main_arena ? NON_MAIN_ARENA : 0));
[c2]  set_head(remainder, remainder_size | PREV_INUSE);