[PATCH] kcsan: test: don't put the expect array on the stack

[PATCH] kcsan: test: don't put the expect array on the stack

[Max Filippov]

Size of the 'expect' array in the __report_matches is 1536 bytes, which
is exactly the default frame size warning limit of the xtensa
architecture.
As a result allmodconfig xtensa kernel builds with the gcc that does not
support the compiler plugins (which otherwise would push the said
warning limit to 2K) fail with the following message:

  kernel/kcsan/kcsan_test.c:257:1: error: the frame size of 1680 bytes
    is larger than 1536 bytes

Fix it by dynamically alocating the 'expect' array.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
---
 kernel/kcsan/kcsan_test.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
index dcec1b743c69..af62ec51bd5f 100644
--- a/kernel/kcsan/kcsan_test.c
+++ b/kernel/kcsan/kcsan_test.c
@@ -159,7 +159,7 @@ static bool __report_matches(const struct expect_report *r)
 	const bool is_assert = (r->access[0].type | r->access[1].type) & KCSAN_ACCESS_ASSERT;
 	bool ret = false;
 	unsigned long flags;
-	typeof(observed.lines) expect;
+	typeof(*observed.lines) *expect;
 	const char *end;
 	char *cur;
 	int i;
@@ -168,6 +168,10 @@ static bool __report_matches(const struct expect_report *r)
 	if (!report_available())
 		return false;
 
+	expect = kmalloc(sizeof(observed.lines), GFP_KERNEL);
+	if (!expect)
+		return false;
+
 	/* Generate expected report contents. */
 
 	/* Title */
@@ -253,6 +257,7 @@ static bool __report_matches(const struct expect_report *r)
 		strstr(observed.lines[2], expect[1])));
 out:
 	spin_unlock_irqrestore(&observed.lock, flags);
+	kfree(expect);
 	return ret;
 }
 
-- 
2.30.2

Re: [PATCH] kcsan: test: don't put the expect array on the stack

[Marco Elver]

On Fri, 23 Dec 2022 at 08:42, Max Filippov <jcmvbkbc@gmail.com> wrote:
>
> Size of the 'expect' array in the __report_matches is 1536 bytes, which
> is exactly the default frame size warning limit of the xtensa
> architecture.
> As a result allmodconfig xtensa kernel builds with the gcc that does not
> support the compiler plugins (which otherwise would push the said
> warning limit to 2K) fail with the following message:
>
>   kernel/kcsan/kcsan_test.c:257:1: error: the frame size of 1680 bytes
>     is larger than 1536 bytes
>
> Fix it by dynamically alocating the 'expect' array.
>
> Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
> ---
>  kernel/kcsan/kcsan_test.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/kcsan/kcsan_test.c b/kernel/kcsan/kcsan_test.c
> index dcec1b743c69..af62ec51bd5f 100644
> --- a/kernel/kcsan/kcsan_test.c
> +++ b/kernel/kcsan/kcsan_test.c
> @@ -159,7 +159,7 @@ static bool __report_matches(const struct expect_report *r)
>         const bool is_assert = (r->access[0].type | r->access[1].type) & KCSAN_ACCESS_ASSERT;
>         bool ret = false;
>         unsigned long flags;
> -       typeof(observed.lines) expect;
> +       typeof(*observed.lines) *expect;
>         const char *end;
>         char *cur;
>         int i;
> @@ -168,6 +168,10 @@ static bool __report_matches(const struct expect_report *r)
>         if (!report_available())
>                 return false;
>
> +       expect = kmalloc(sizeof(observed.lines), GFP_KERNEL);
> +       if (!expect)

WARN_ON(), because this may either spuriously fail or pass a test
case, and we'd want to know about that.

Thanks,
-- Marco