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

Samuel Holland
2024-03-27T15:11:37Z

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