objtool: Introduce CFI hash

commit 8b946cc3 upstream.

Andi reported that objtool on vmlinux.o consumes more memory than his
system has, leading to horrific performance.

This is in part because we keep a struct instruction for every
instruction in the file in-memory. Shrink struct instruction by
removing the CFI state (which includes full register state) from it
and demand allocating it.

Given most instructions don't actually change CFI state, there's lots
of repetition there, so add a hash table to find previous CFI
instances.

Reduces memory consumption (and runtime) for processing an
x86_64-allyesconfig:

  pre:  4:40.84 real,   143.99 user,    44.18 sys,      30624988 mem
  post: 2:14.61 real,   108.58 user,    25.04 sys,      16396184 mem

Suggested-by: Andi Kleen <andi@firstfloor.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210624095147.756759107@infradead.org


Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
[bwh: Backported to 5.10:
 - Don't use bswap_if_needed() since we don't have any of the other fixes
   for mixed-endian cross-compilation
 - Since we don't have "objtool: Rewrite hashtable sizing", make
   cfi_hash_alloc() set the number of bits similarly to elf_hash_bits()
 - objtool doesn't have any mcount handling
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>