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MIPS: memset.S: Add comments to fault fixup handlers

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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>
This commit is contained in:
Matt Redfearn 2018-05-23 14:39:59 +01:00 committed by Paul Burton
parent b1c03f1ef4
commit 6312455a04
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1 changed files with 18 additions and 0 deletions
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18
arch/mips/lib/memset.S
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@ -232,16 +232,25 @@
#ifdef CONFIG_CPU_MIPSR6 #ifdef CONFIG_CPU_MIPSR6
.Lbyte_fixup\@: .Lbyte_fixup\@:
/*
* unset_bytes = (#bytes - (#unaligned bytes)) - (-#unaligned bytes remaining + 1) + 1
* a2 = a2 - t0 + 1
*/
PTR_SUBU a2, t0 PTR_SUBU a2, t0
jr ra jr ra
PTR_ADDIU a2, 1 PTR_ADDIU a2, 1
#endif /* CONFIG_CPU_MIPSR6 */ #endif /* CONFIG_CPU_MIPSR6 */
.Lfirst_fixup\@: .Lfirst_fixup\@:
/* unset_bytes already in a2 */
jr ra jr ra
nop nop
.Lfwd_fixup\@: .Lfwd_fixup\@:
/*
* unset_bytes = partial_start_addr + #bytes - fault_addr
* a2 = t1 + (a2 & 3f) - $28->task->BUADDR
*/
PTR_L t0, TI_TASK($28) PTR_L t0, TI_TASK($28)
andi a2, 0x3f andi a2, 0x3f
LONG_L t0, THREAD_BUADDR(t0) LONG_L t0, THREAD_BUADDR(t0)
@ -250,6 +259,10 @@
LONG_SUBU a2, t0 LONG_SUBU a2, t0
.Lpartial_fixup\@: .Lpartial_fixup\@:
/*
* unset_bytes = partial_end_addr + #bytes - fault_addr
* a2 = a0 + (a2 & STORMASK) - $28->task->BUADDR
*/
PTR_L t0, TI_TASK($28) PTR_L t0, TI_TASK($28)
andi a2, STORMASK andi a2, STORMASK
LONG_L t0, THREAD_BUADDR(t0) LONG_L t0, THREAD_BUADDR(t0)
@ -258,10 +271,15 @@
LONG_SUBU a2, t0 LONG_SUBU a2, t0
.Llast_fixup\@: .Llast_fixup\@:
/* unset_bytes already in a2 */
jr ra jr ra
nop nop
.Lsmall_fixup\@: .Lsmall_fixup\@:
/*
* unset_bytes = end_addr - current_addr + 1
* a2 = t1 - a0 + 1
*/
PTR_SUBU a2, t1, a0 PTR_SUBU a2, t1, a0
jr ra jr ra
PTR_ADDIU a2, 1 PTR_ADDIU a2, 1