MIPS: memset: Fix CPU_DADDI_WORKAROUNDS `small_fixup' regression

Fix a commit 8a8158c85e1e ("MIPS: memset.S: EVA & fault support for
small_memset") regression and remove assembly warnings:

arch/mips/lib/memset.S: Assembler messages:
arch/mips/lib/memset.S:243: Warning: Macro instruction expanded into multiple instructions in a branch delay slot

triggering with the CPU_DADDI_WORKAROUNDS option set and this code:

	PTR_SUBU	a2, t1, a0
	jr		ra
	 PTR_ADDIU	a2, 1

This is because with that option in place the DADDIU instruction, which
the PTR_ADDIU CPP macro expands to, becomes a GAS macro, which in turn
expands to an LI/DADDU (or actually ADDIU/DADDU) sequence:

 13c:	01a4302f 	dsubu	a2,t1,a0
 140:	03e00008 	jr	ra
 144:	24010001 	li	at,1
 148:	00c1302d 	daddu	a2,a2,at
	...

Correct this by switching off the `noreorder' assembly mode and letting
GAS schedule this jump's delay slot, as there is nothing special about
it that would require manual scheduling.  With this change in place
correct code is produced:

 13c:	01a4302f 	dsubu	a2,t1,a0
 140:	24010001 	li	at,1
 144:	03e00008 	jr	ra
 148:	00c1302d 	daddu	a2,a2,at
	...

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: 8a8158c85e1e ("MIPS: memset.S: EVA & fault support for small_memset")
Patchwork: https://patchwork.linux-mips.org/patch/20833/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: stable@vger.kernel.org # 4.17+

diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S
index 3a6f34ef5ffc38edf71fe616b2888af9b6dc6f30..069acec3df9f05df3bcea2ff507a8d8763fa60d0 100644 (file)
--- a/arch/mips/lib/memset.S
+++ b/arch/mips/lib/memset.S
@@ -280,9 +280,11 @@
         * unset_bytes = end_addr - current_addr + 1
         *      a2     =    t1    -      a0      + 1
         */
+       .set            reorder
        PTR_SUBU        a2, t1, a0
+       PTR_ADDIU       a2, 1
        jr              ra
-        PTR_ADDIU      a2, 1
+       .set            noreorder
 
        .endm