On arm32, size_t is defined to be unsigned int, while PAGE_SIZE is
unsigned long. This hence triggers a compilation warning as min()
asserts the type of two operands to be equal. Casting PAGE_SIZE to size_t
solves this issue and works on other target architectures as well.

Compilation warning details:

kernel/trace/trace.c: In function 'tracing_splice_read_pipe':
./include/linux/minmax.h:20:28: warning: comparison of distinct pointer types lacks a cast
  (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                            ^
./include/linux/minmax.h:26:4: note: in expansion of macro '__typecheck'
   (__typecheck(x, y) && __no_side_effects(x, y))
    ^~~~~~~~~~~

...

kernel/trace/trace.c:6771:8: note: in expansion of macro 'min'
        min((size_t)trace_seq_used(&iter->seq),
        ^~~

Fixes: f5178c41bb43 ("tracing: Fix oob write in trace_seq_to_buffer()")
Signed-off-by: Pan Taixi <pantaixi@huaweicloud.com>
---
 kernel/trace/trace.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5b8db27fb6ef..766cb3cd254e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6824,7 +6824,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
 		ret = trace_seq_to_buffer(&iter->seq,
 					  page_address(spd.pages[i]),
 					  min((size_t)trace_seq_used(&iter->seq),
-						  PAGE_SIZE));
+						  (size_t)PAGE_SIZE));
 		if (ret < 0) {
 			__free_page(spd.pages[i]);
 			break;
-- 
2.34.1

Pan Taixi <pantaixi@huaweicloud.com> wrote:
>
> On arm32, size_t is defined to be unsigned int, while PAGE_SIZE is
> unsigned long. This hence triggers a compilation warning as min()
> asserts the type of two operands to be equal. Casting PAGE_SIZE to size_t
> solves this issue and works on other target architectures as well.
>

Thanks! I forgot to cast PAGE_SIZE to size_t

Reviewed-by: Jeongjun Park <aha310510@gmail.com>

> Compilation warning details:
>
> kernel/trace/trace.c: In function 'tracing_splice_read_pipe':
> ./include/linux/minmax.h:20:28: warning: comparison of distinct pointer types lacks a cast
>   (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
>                             ^
> ./include/linux/minmax.h:26:4: note: in expansion of macro '__typecheck'
>    (__typecheck(x, y) && __no_side_effects(x, y))
>     ^~~~~~~~~~~
>
> ...
>
> kernel/trace/trace.c:6771:8: note: in expansion of macro 'min'
>         min((size_t)trace_seq_used(&iter->seq),
>         ^~~
>
> Fixes: f5178c41bb43 ("tracing: Fix oob write in trace_seq_to_buffer()")
> Signed-off-by: Pan Taixi <pantaixi@huaweicloud.com>
> ---
>  kernel/trace/trace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 5b8db27fb6ef..766cb3cd254e 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6824,7 +6824,7 @@ static ssize_t tracing_splice_read_pipe(struct file *filp,
>                 ret = trace_seq_to_buffer(&iter->seq,
>                                           page_address(spd.pages[i]),
>                                           min((size_t)trace_seq_used(&iter->seq),
> -                                                 PAGE_SIZE));
> +                                                 (size_t)PAGE_SIZE));
>                 if (ret < 0) {
>                         __free_page(spd.pages[i]);
>                         break;
> --
> 2.34.1
>