kunit: split out part of kunit_assert into a static const

This is per Linus's suggestion in [1].

The issue there is that every KUNIT_EXPECT/KUNIT_ASSERT puts a
kunit_assert object onto the stack. Normally we rely on compilers to
elide this, but when that doesn't work out, this blows up the stack
usage of kunit test functions.

We can move some data off the stack by making it static.
This change introduces a new `struct kunit_loc` to hold the file and
line number and then just passing assert_type (EXPECT or ASSERT) as an
argument.

In [1], it was suggested to also move out the format string as well, but
users could theoretically craft a format string at runtime, so we can't.

This change leaves a copy of `assert_type` in kunit_assert for now
because cleaning up all the macros to not pass it around is a bit more
involved.

Here's an example of the expanded code for KUNIT_FAIL():
if (__builtin_expect(!!(!(false)), 0)) {
  static const struct kunit_loc loc = { .file = ... };
  struct kunit_fail_assert __assertion = { .assert = { .type ...  };
  kunit_do_failed_assertion(test, &loc, KUNIT_EXPECTATION, &__assertion.assert, ...);
};

[1] https://groups.google.com/g/kunit-dev/c/i3fZXgvBrfA/m/VULQg1z6BAAJ

Signed-off-by: Daniel Latypov <dlatypov@google.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

2 files changed, 14 insertions, 10 deletions

diff --git a/lib/kunit/assert.c b/lib/kunit/assert.c
index 4d9a1295efc7..9f4492a8e24e 100644
--- a/lib/kunit/assert.c
+++ b/lib/kunit/assert.c
@@ -10,12 +10,13 @@
 
 #include "string-stream.h"
 
-void kunit_base_assert_format(const struct kunit_assert *assert,
+void kunit_assert_prologue(const struct kunit_loc *loc,
+			   enum kunit_assert_type type,
 			      struct string_stream *stream)
 {
 	const char *expect_or_assert = NULL;
 
-	switch (assert->type) {
+	switch (type) {
 	case KUNIT_EXPECTATION:
 		expect_or_assert = "EXPECTATION";
 		break;
@@ -25,9 +26,9 @@ void kunit_base_assert_format(const struct kunit_assert *assert,
 	}
 
 	string_stream_add(stream, "%s FAILED at %s:%d\n",
-			  expect_or_assert, assert->file, assert->line);
+			  expect_or_assert, loc->file, loc->line);
 }
-EXPORT_SYMBOL_GPL(kunit_base_assert_format);
+EXPORT_SYMBOL_GPL(kunit_assert_prologue);
 
 void kunit_assert_print_msg(const struct kunit_assert *assert,
 			    struct string_stream *stream)
diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index 345a9dd88c27..7dec3248562f 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -240,7 +240,8 @@ static void kunit_print_string_stream(struct kunit *test,
 	}
 }
 
-static void kunit_fail(struct kunit *test, struct kunit_assert *assert)
+static void kunit_fail(struct kunit *test, const struct kunit_loc *loc,
+		       enum kunit_assert_type type, struct kunit_assert *assert)
 {
 	struct string_stream *stream;
 
@@ -250,12 +251,12 @@ static void kunit_fail(struct kunit *test, struct kunit_assert *assert)
 	if (!stream) {
 		WARN(true,
 		     "Could not allocate stream to print failed assertion in %s:%d\n",
-		     assert->file,
-		     assert->line);
+		     loc->file,
+		     loc->line);
 		return;
 	}
 
-	kunit_base_assert_format(assert, stream);
+	kunit_assert_prologue(loc, type, stream);
 	assert->format(assert, stream);
 
 	kunit_print_string_stream(test, stream);
@@ -277,6 +278,8 @@ static void __noreturn kunit_abort(struct kunit *test)
 }
 
 void kunit_do_failed_assertion(struct kunit *test,
+			       const struct kunit_loc *loc,
+			       enum kunit_assert_type type,
 			       struct kunit_assert *assert,
 			       const char *fmt, ...)
 {
@@ -286,11 +289,11 @@ void kunit_do_failed_assertion(struct kunit *test,
 	assert->message.fmt = fmt;
 	assert->message.va = &args;
 
-	kunit_fail(test, assert);
+	kunit_fail(test, loc, type, assert);
 
 	va_end(args);
 
-	if (assert->type == KUNIT_ASSERTION)
+	if (type == KUNIT_ASSERTION)
 		kunit_abort(test);
 }
 EXPORT_SYMBOL_GPL(kunit_do_failed_assertion);