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authorMatt Redfearn <matt.redfearn@mips.com>2018-05-23 14:39:59 +0100
committerPaul Burton <paul.burton@mips.com>2018-07-24 17:02:43 -0700
commit6312455a0437a64059bdeee5696b375593a09947 (patch)
treee03d927f4eb75d8cf87434fa7fc6d6ed90623545 /arch/mips/lib
parentb1c03f1ef48d36ff28afb06e8f0c1233ef072f1d (diff)
downloadlinux-6312455a0437a64059bdeee5696b375593a09947.tar.bz2
MIPS: memset.S: Add comments to fault fixup handlers
It is not immediately obvious what the expected inputs to these fault handlers is and how they calculate the number of unset bytes. Having stared deeply at this in order to fix some corner cases, add some comments to assist those who follow. Signed-off-by: Matt Redfearn <matt.redfearn@mips.com> Signed-off-by: Paul Burton <paul.burton@mips.com> Patchwork: https://patchwork.linux-mips.org/patch/19339/ Cc: James Hogan <jhogan@kernel.org> Cc: Ralf Baechle <ralf@linux-mips.org> Cc: <linux-mips@linux-mips.org> Cc: <linux-kernel@vger.kernel.org>
Diffstat (limited to 'arch/mips/lib')
-rw-r--r--arch/mips/lib/memset.S18
1 files changed, 18 insertions, 0 deletions
diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S
index fac26ce64b2f..3a6f34ef5ffc 100644
--- a/arch/mips/lib/memset.S
+++ b/arch/mips/lib/memset.S
@@ -232,16 +232,25 @@
#ifdef CONFIG_CPU_MIPSR6
.Lbyte_fixup\@:
+ /*
+ * unset_bytes = (#bytes - (#unaligned bytes)) - (-#unaligned bytes remaining + 1) + 1
+ * a2 = a2 - t0 + 1
+ */
PTR_SUBU a2, t0
jr ra
PTR_ADDIU a2, 1
#endif /* CONFIG_CPU_MIPSR6 */
.Lfirst_fixup\@:
+ /* unset_bytes already in a2 */
jr ra
nop
.Lfwd_fixup\@:
+ /*
+ * unset_bytes = partial_start_addr + #bytes - fault_addr
+ * a2 = t1 + (a2 & 3f) - $28->task->BUADDR
+ */
PTR_L t0, TI_TASK($28)
andi a2, 0x3f
LONG_L t0, THREAD_BUADDR(t0)
@@ -250,6 +259,10 @@
LONG_SUBU a2, t0
.Lpartial_fixup\@:
+ /*
+ * unset_bytes = partial_end_addr + #bytes - fault_addr
+ * a2 = a0 + (a2 & STORMASK) - $28->task->BUADDR
+ */
PTR_L t0, TI_TASK($28)
andi a2, STORMASK
LONG_L t0, THREAD_BUADDR(t0)
@@ -258,10 +271,15 @@
LONG_SUBU a2, t0
.Llast_fixup\@:
+ /* unset_bytes already in a2 */
jr ra
nop
.Lsmall_fixup\@:
+ /*
+ * unset_bytes = end_addr - current_addr + 1
+ * a2 = t1 - a0 + 1
+ */
PTR_SUBU a2, t1, a0
jr ra
PTR_ADDIU a2, 1