/* We overlay this structure on the user-data portion of a chunk when
   the chunk is stored in the per-thread cache.  */
typedef struct tcache_entry
{
  struct tcache_entry *next;
} tcache_entry;

/* There is one of these for each thread, which contains the
   per-thread cache (hence "tcache_perthread_struct").  Keeping
   overall size low is mildly important.  Note that COUNTS and ENTRIES
   are redundant (we could have just counted the linked list each
   time), this is for performance reasons.  */
typedef struct tcache_perthread_struct
{
  char counts[TCACHE_MAX_BINS];
  tcache_entry *entries[TCACHE_MAX_BINS];
} tcache_perthread_struct;

pwndbg> x/10gx 0x8403000
0x8403000:      0x0000000000000000      0x0000000000000251
0x8403010:      0x0100000002000000      0x0100000000000000
0x8403020:      0x0000000000000000      0x0000000000000000
0x8403030:      0x0000000000000000      0x0000000000000000
0x8403040:      0x0000000000000000      0x0000000000000000
pwndbg> bin
tcachebins
0x50 [  2]: 0x8403260 ◂— 0x8403260
0x90 [  1]: 0x84032b0 ◂— 0x0
0x110 [  1]: 0x8403340 ◂— 0x0

/* Only used to pre-fill the tunables.  */
# define tidx2usize(idx)	(((size_t) idx) * MALLOC_ALIGNMENT + MINSIZE - SIZE_SZ)

/* When "x" is from chunksize().  */
# define csize2tidx(x) (((x) - MINSIZE + MALLOC_ALIGNMENT - 1) / MALLOC_ALIGNMENT)
/* When "x" is a user-provided size.  */
# define usize2tidx(x) csize2tidx (request2size (x))