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

Björn Töpel
2024-02-19T14:15:34Z

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