lkml.org 
[lkml]   [2018]   [May]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v3 2/2] MIPS: memset.S: Add comments to fault fixup handlers
Date
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>
---

Changes in v3:
- Update comment on .Lbyte_fixup to reflect corrected behavior

Changes in v2:
- Add comments to fault handlers in new, separate, patch.

arch/mips/lib/memset.S | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/arch/mips/lib/memset.S b/arch/mips/lib/memset.S
index fac26ce64b2..3a6f34ef5ff 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
--
2.7.4
\
 
 \ /
  Last update: 2018-05-23 15:51    [W:0.097 / U:0.268 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site