[v1] riscv: Various text patching improvements

[PATCH 4/7] riscv: Simplify text patching loops

Posted by Samuel Holland 1 year, 12 months ago

This reduces the number of variables and makes the code easier to parse.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
---

 arch/riscv/kernel/patch.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index bccd9ed04a05..7f030b46eae5 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -155,7 +155,6 @@ NOKPROBE_SYMBOL(__patch_insn_write);
 
 static int patch_insn_set(void *addr, u8 c, size_t len)
 {
-	size_t patched = 0;
 	size_t size;
 	int ret = 0;
 
@@ -163,11 +162,12 @@ static int patch_insn_set(void *addr, u8 c, size_t len)
 	 * __patch_insn_set() can only work on 2 pages at a time so call it in a
 	 * loop with len <= 2 * PAGE_SIZE.
 	 */
-	while (patched < len && !ret) {
-		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
-		ret = __patch_insn_set(addr + patched, c, size);
+	while (len && !ret) {
+		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
+		ret = __patch_insn_set(addr, c, size);
 
-		patched += size;
+		addr += size;
+		len -= size;
 	}
 
 	return ret;
@@ -190,7 +190,6 @@ NOKPROBE_SYMBOL(patch_text_set_nosync);
 
 int patch_insn_write(void *addr, const void *insn, size_t len)
 {
-	size_t patched = 0;
 	size_t size;
 	int ret = 0;
 
@@ -198,11 +197,13 @@ int patch_insn_write(void *addr, const void *insn, size_t len)
 	 * Copy the instructions to the destination address, two pages at a time
 	 * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
 	 */
-	while (patched < len && !ret) {
-		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
-		ret = __patch_insn_write(addr + patched, insn + patched, size);
+	while (len && !ret) {
+		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
+		ret = __patch_insn_write(addr, insn, size);
 
-		patched += size;
+		addr += size;
+		insn += size;
+		len -= size;
 	}
 
 	return ret;
-- 
2.43.0

Re: [PATCH 4/7] riscv: Simplify text patching loops

Posted by Björn Töpel 1 year, 11 months ago

Samuel Holland <samuel.holland@sifive.com> writes:

> This reduces the number of variables and makes the code easier to parse.
>
> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
> ---
>
>  arch/riscv/kernel/patch.c | 21 +++++++++++----------
>  1 file changed, 11 insertions(+), 10 deletions(-)
>
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index bccd9ed04a05..7f030b46eae5 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -155,7 +155,6 @@ NOKPROBE_SYMBOL(__patch_insn_write);
>  
>  static int patch_insn_set(void *addr, u8 c, size_t len)
>  {
> -	size_t patched = 0;
>  	size_t size;
>  	int ret = 0;
>  
> @@ -163,11 +162,12 @@ static int patch_insn_set(void *addr, u8 c, size_t len)
>  	 * __patch_insn_set() can only work on 2 pages at a time so call it in a
>  	 * loop with len <= 2 * PAGE_SIZE.
>  	 */
> -	while (patched < len && !ret) {
> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
> -		ret = __patch_insn_set(addr + patched, c, size);
> +	while (len && !ret) {
> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
> +		ret = __patch_insn_set(addr, c, size);

While you're at it, do:
  ret = __patch_insn_set(addr, c, size);
  if (ret)
          return ret;
  ...
return 0;
}

and simplify the while-loop predicate?

>  
> -		patched += size;
> +		addr += size;
> +		len -= size;
>  	}
>  
>  	return ret;
> @@ -190,7 +190,6 @@ NOKPROBE_SYMBOL(patch_text_set_nosync);
>  
>  int patch_insn_write(void *addr, const void *insn, size_t len)
>  {
> -	size_t patched = 0;
>  	size_t size;
>  	int ret = 0;
>  
> @@ -198,11 +197,13 @@ int patch_insn_write(void *addr, const void *insn, size_t len)
>  	 * Copy the instructions to the destination address, two pages at a time
>  	 * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
>  	 */
> -	while (patched < len && !ret) {
> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
> -		ret = __patch_insn_write(addr + patched, insn + patched, size);
> +	while (len && !ret) {
> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
> +		ret = __patch_insn_write(addr, insn, size);

Same comment as above.


Björn

Re: [PATCH 4/7] riscv: Simplify text patching loops

Posted by Samuel Holland 1 year, 10 months ago

Hi Björn,

On 2024-02-19 7:03 AM, Björn Töpel wrote:
> Samuel Holland <samuel.holland@sifive.com> writes:
> 
>> This reduces the number of variables and makes the code easier to parse.
>>
>> Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
>> ---
>>
>>  arch/riscv/kernel/patch.c | 21 +++++++++++----------
>>  1 file changed, 11 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
>> index bccd9ed04a05..7f030b46eae5 100644
>> --- a/arch/riscv/kernel/patch.c
>> +++ b/arch/riscv/kernel/patch.c
>> @@ -155,7 +155,6 @@ NOKPROBE_SYMBOL(__patch_insn_write);
>>  
>>  static int patch_insn_set(void *addr, u8 c, size_t len)
>>  {
>> -	size_t patched = 0;
>>  	size_t size;
>>  	int ret = 0;
>>  
>> @@ -163,11 +162,12 @@ static int patch_insn_set(void *addr, u8 c, size_t len)
>>  	 * __patch_insn_set() can only work on 2 pages at a time so call it in a
>>  	 * loop with len <= 2 * PAGE_SIZE.
>>  	 */
>> -	while (patched < len && !ret) {
>> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
>> -		ret = __patch_insn_set(addr + patched, c, size);
>> +	while (len && !ret) {
>> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
>> +		ret = __patch_insn_set(addr, c, size);
> 
> While you're at it, do:
>   ret = __patch_insn_set(addr, c, size);
>   if (ret)
>           return ret;
>   ...
> return 0;
> }
> 
> and simplify the while-loop predicate?

Yes, this looks better and reduces the code size as well. I'll make this change
in v2.

Regards,
Samuel

>>  
>> -		patched += size;
>> +		addr += size;
>> +		len -= size;
>>  	}
>>  
>>  	return ret;
>> @@ -190,7 +190,6 @@ NOKPROBE_SYMBOL(patch_text_set_nosync);
>>  
>>  int patch_insn_write(void *addr, const void *insn, size_t len)
>>  {
>> -	size_t patched = 0;
>>  	size_t size;
>>  	int ret = 0;
>>  
>> @@ -198,11 +197,13 @@ int patch_insn_write(void *addr, const void *insn, size_t len)
>>  	 * Copy the instructions to the destination address, two pages at a time
>>  	 * because __patch_insn_write() can only handle len <= 2 * PAGE_SIZE.
>>  	 */
>> -	while (patched < len && !ret) {
>> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
>> -		ret = __patch_insn_write(addr + patched, insn + patched, size);
>> +	while (len && !ret) {
>> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
>> +		ret = __patch_insn_write(addr, insn, size);
> 
> Same comment as above.
> 
> 
> Björn

RE: [PATCH 4/7] riscv: Simplify text patching loops

Posted by David Laight 1 year, 11 months ago

...
> > -	while (patched < len && !ret) {
> > -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
> > -		ret = __patch_insn_set(addr + patched, c, size);
> > +	while (len && !ret) {
> > +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);

Does that need to be min_t()?
Both arguments seem to be unsigned.
(Did it even ever need to be?)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH 4/7] riscv: Simplify text patching loops

Posted by Samuel Holland 1 year, 10 months ago

Hi David,

On 2024-02-19 4:13 PM, David Laight wrote:
> ...
>>> -	while (patched < len && !ret) {
>>> -		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr + patched), len - patched);
>>> -		ret = __patch_insn_set(addr + patched, c, size);
>>> +	while (len && !ret) {
>>> +		size = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(addr), len);
> 
> Does that need to be min_t()?
> Both arguments seem to be unsigned.
> (Did it even ever need to be?)

You're right, this never needed min_t(). I'll update this for v2.

Regards,
Samuel