[PATCH] fat: avoid stack overflow warning

[Arnd Bergmann <arnd@kernel.org>]

From: Arnd Bergmann <arnd@arndb.de>

Building the fat kunit tests on with -fsanitize=alignment
reveals some rather excessive stack usage:

fs/fat/fat_test.c: In function 'fat_clus_to_blknr_test':
fs/fat/fat_test.c:33:1: error: the frame size of 4736 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]
   33 | }
      | ^
fs/fat/fat_test.c: In function 'fat_get_blknr_offset_test':
fs/fat/fat_test.c:52:1: error: the frame size of 4800 bytes is larger than 1536 bytes [-Werror=frame-larger-than=]

The problem is clearly related to the on-stack copy of a local
msdos_sb_info structure. Avoid this by making that copy
'static const' and changing the called functions to accept
a constant input.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 fs/fat/fat.h      | 4 ++--
 fs/fat/fat_test.c | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/fat/fat.h b/fs/fat/fat.h
index 5a58f0bf8ce8..52bced59abe4 100644
--- a/fs/fat/fat.h
+++ b/fs/fat/fat.h
@@ -247,13 +247,13 @@ static inline unsigned char fat_checksum(const __u8 *name)
 	return s;
 }
 
-static inline sector_t fat_clus_to_blknr(struct msdos_sb_info *sbi, int clus)
+static inline sector_t fat_clus_to_blknr(const struct msdos_sb_info *sbi, int clus)
 {
 	return ((sector_t)clus - FAT_START_ENT) * sbi->sec_per_clus
 		+ sbi->data_start;
 }
 
-static inline void fat_get_blknr_offset(struct msdos_sb_info *sbi,
+static inline void fat_get_blknr_offset(const struct msdos_sb_info *sbi,
 				loff_t i_pos, sector_t *blknr, int *offset)
 {
 	*blknr = i_pos >> sbi->dir_per_block_bits;
diff --git a/fs/fat/fat_test.c b/fs/fat/fat_test.c
index 4eeed9dca549..9583ce66dca3 100644
--- a/fs/fat/fat_test.c
+++ b/fs/fat/fat_test.c
@@ -22,7 +22,7 @@ static void fat_checksum_test(struct kunit *test)
 
 static void fat_clus_to_blknr_test(struct kunit *test)
 {
-	struct msdos_sb_info sbi = {
+	static const struct msdos_sb_info sbi = {
 		.sec_per_clus = 4,
 		.data_start = 100,
 	};
@@ -34,7 +34,7 @@ static void fat_clus_to_blknr_test(struct kunit *test)
 
 static void fat_get_blknr_offset_test(struct kunit *test)
 {
-	struct msdos_sb_info sbi = {
+	static const struct msdos_sb_info sbi = {
 		.dir_per_block = 16,
 		.dir_per_block_bits = 4,
 	};
-- 
2.39.5