iv/linux
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

arm64: cmpxchg: Use "K" instead of "L" for ll/sc immediate constraint

Browse Source 
commit 4230509978f2921182da4e9197964dccdbe463c3 upstream.

The "L" AArch64 machine constraint, which we use for the "old" value in
an LL/SC cmpxchg(), generates an immediate that is suitable for a 64-bit
logical instruction. However, for cmpxchg() operations on types smaller
than 64 bits, this constraint can result in an invalid instruction which
is correctly rejected by GAS, such as EOR W1, W1, #0xffffffff.

Whilst we could special-case the constraint based on the cmpxchg size,
it's far easier to change the constraint to "K" and put up with using
a register for large 64-bit immediates. For out-of-line LL/SC atomics,
this is all moot anyway.

Reported-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Will Deacon 2018-09-18 09:39:55 +01:00 committed by Greg Kroah-Hartman
parent 73dc3ba7d9
commit 1b62277f4c
1 changed files with 1 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/arm64/include/asm/atomic_ll_sc.h
View File

@ -268,7 +268,7 @@ __LL_SC_PREFIX(__cmpxchg_case_##name##sz(volatile void *ptr, \
"2:" \
: [tmp] "=&r" (tmp), [oldval] "=&r" (oldval), \
[v] "+Q" (*(u##sz *)ptr) \
: [old] "Lr" (old), [new] "r" (new) \
: [old] "Kr" (old), [new] "r" (new) \
: cl); \
\
return oldval; \