> On 24 Oct 2016, at 19:11, David Miller <da...@davemloft.net> wrote:
>
> From: James Clarke <jrt...@jrtc27.com>
> Date: Sat, 22 Oct 2016 10:51:28 +0100
>
>> @@ -19,12 +19,20 @@ void arch_jump_label_transform(struct jump_entry *entry,
>> if (type == JUMP_LABEL_JMP) {
>> s32 off = (s32)entry->target - (s32)entry->code;
>>
>> + BUG_ON(off & 3);
>> +
>> #ifdef CONFIG_SPARC64
>> - /* ba,pt %xcc, . + (off << 2) */
>> - val = 0x10680000 | ((u32) off >> 2);
>> + /* WDISP19 - target is . + (immed << 2) */
>> + BUG_ON(off > 0xfffff);
>> + BUG_ON(off < -0x100000);
>> + /* ba,pt %xcc, . + off */
>> + val = 0x10680000 | (((u32) off >> 2) & 0x7ffff);
>> #else
>> - /* ba . + (off << 2) */
>> - val = 0x10800000 | ((u32) off >> 2);
>> + /* WDISP22 - target is . + (immed << 2) */
>> + BUG_ON(off > 0x7fffff);
>> + BUG_ON(off < -0x800000);
>> + /* ba . + off */
>> + val = 0x10800000 | (((u32) off >> 2) & 0x3fffff);
>> #endif
>
> Since we can determine at run time whether we need to use a non-v9
> branch or not, it makes no sense to fail when a v9 branch is out of
> range.
>
> We can simply downgrade to a pre-v9 one.
>
> Something like this:
>
> diff --git a/arch/sparc/kernel/jump_label.c b/arch/sparc/kernel/jump_label.c
> index 59bbeff..689e557 100644
> --- a/arch/sparc/kernel/jump_label.c
> +++ b/arch/sparc/kernel/jump_label.c
> @@ -13,19 +13,24 @@
> void arch_jump_label_transform(struct jump_entry *entry,
> enum jump_label_type type)
> {
> - u32 val;
> u32 *insn = (u32 *) (unsigned long) entry->code;
> + u32 val;
>
> if (type == JUMP_LABEL_JMP) {
> s32 off = (s32)entry->target - (s32)entry->code;
> + bool use_v9_branch = false;
>
> #ifdef CONFIG_SPARC64
> - /* ba,pt %xcc, . + (off << 2) */
> - val = 0x10680000 | ((u32) off >> 2);
> -#else
> - /* ba . + (off << 2) */
> - val = 0x10800000 | ((u32) off >> 2);
> + if (off <= 0xfffff && off >= -0x100000)
> + use_v9_branch = true;
> #endif
> + if (use_v9_branch) {
> + /* ba,pt %xcc, . + (off << 2) */
> + val = 0x10680000 | (((u32) off >> 2) & 0x7ffff);
> + } else {
> + /* ba . + (off << 2) */
> + val = 0x10800000 | (((u32) off >> 2) & 0x3fffff);
> + }
> } else {
> val = 0x01000000;
> }
Sure, that makes sense; updated and tested for a few hours:
From d5997fd98fc80d1ceabe11f6fcd63dfce99b8253 Mon Sep 17 00:00:00 2001
From: James Clarke <jrt...@jrtc27.com>
Date: Mon, 24 Oct 2016 19:49:25 +0100
Subject: [PATCH v2] sparc: Handle negative offsets in
arch_jump_label_transform
Additionally, if the offset will overflow the immediate for a ba,pt
instruction, fall back on a standard ba to get an extra 3 bits.
Signed-off-by: James Clarke <jrt...@jrtc27.com>
---
arch/sparc/kernel/jump_label.c | 23 +++++++++++++++++------
1 file changed, 17 insertions(+), 6 deletions(-)
diff --git a/arch/sparc/kernel/jump_label.c b/arch/sparc/kernel/jump_label.c
index 59bbeff..07933b9 100644
--- a/arch/sparc/kernel/jump_label.c
+++ b/arch/sparc/kernel/jump_label.c
@@ -13,19 +13,30 @@
void arch_jump_label_transform(struct jump_entry *entry,
enum jump_label_type type)
{
- u32 val;
u32 *insn = (u32 *) (unsigned long) entry->code;
+ u32 val;
if (type == JUMP_LABEL_JMP) {
s32 off = (s32)entry->target - (s32)entry->code;
+ bool use_v9_branch = false;
+
+ BUG_ON(off & 3);
#ifdef CONFIG_SPARC64
- /* ba,pt %xcc, . + (off << 2) */
- val = 0x10680000 | ((u32) off >> 2);
-#else
- /* ba . + (off << 2) */
- val = 0x10800000 | ((u32) off >> 2);
+ if (off <= 0xfffff && off >= -0x100000)
+ use_v9_branch = true;
#endif
+ if (use_v9_branch) {
+ /* WDISP19 - target is . + immed << 2 */
+ /* ba,pt %xcc, . + off */
+ val = 0x10680000 | (((u32) off >> 2) & 0x7ffff);
+ } else {
+ /* WDISP22 - target is . + immed << 2 */
+ BUG_ON(off > 0x7fffff);
+ BUG_ON(off < -0x800000);
+ /* ba . + off */
+ val = 0x10800000 | (((u32) off >> 2) & 0x3fffff);
+ }
} else {
val = 0x01000000;
}
--
2.9.3
