The cmpxchg implementation introduced by commit
c342f78217e8 ("arm64:
cmpxchg: patch in lse instructions when supported by the CPU") performs
an apparently redundant register move of [old] to [oldval] in the
success case - it always uses the same register width as [oldval] was
originally loaded with, and is only executed when [old] and [oldval] are
known to be equal anyway.
The only effect it seemingly does have is to take up a surprising amount
of space in the kernel text, as removing it reveals:
text data bss dec hex filename
12426658 1348614 4499749 18275021 116dacd vmlinux.o.new
12429238 1348614 4499749 18277601 116e4e1 vmlinux.o.old
Reviewed-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
" st" #rel "xr" #sz "\t%w[tmp], %" #w "[new], %[v]\n" \
" cbnz %w[tmp], 1b\n" \
" " #mb "\n" \
- " mov %" #w "[oldval], %" #w "[old]\n" \
"2:" \
: [tmp] "=&r" (tmp), [oldval] "=&r" (oldval), \
[v] "+Q" (*(unsigned long *)ptr) \