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mtd: avoid stack overflow in MTD CFI code

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When map_word gets too large, we use a lot of kernel stack, and for
MTD_MAP_BANK_WIDTH_32, this means we use more than the recommended
1024 bytes in a number of functions:

drivers/mtd/chips/cfi_cmdset_0020.c: In function 'cfi_staa_write_buffers':
drivers/mtd/chips/cfi_cmdset_0020.c:651:1: warning: the frame size of 1336 bytes is larger than 1024 bytes [-Wframe-larger-than=]
drivers/mtd/chips/cfi_cmdset_0020.c: In function 'cfi_staa_erase_varsize':
drivers/mtd/chips/cfi_cmdset_0020.c:972:1: warning: the frame size of 1208 bytes is larger than 1024 bytes [-Wframe-larger-than=]
drivers/mtd/chips/cfi_cmdset_0001.c: In function 'do_write_buffer':
drivers/mtd/chips/cfi_cmdset_0001.c:1835:1: warning: the frame size of 1240 bytes is larger than 1024 bytes [-Wframe-larger-than=]

This can be avoided if all operations on the map word are done
indirectly and the stack gets reused between the calls. We can
mostly achieve this by selecting MTD_COMPLEX_MAPPINGS whenever
MTD_MAP_BANK_WIDTH_32 is set, but for the case that no other
bank width is enabled, we also need to use a non-constant
map_bankwidth() to convince the compiler to use less stack.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
[Brian: this patch mostly achieves its goal by forcing
    MTD_COMPLEX_MAPPINGS (and the accompanying indirection) for 256-bit
    mappings; the rest of the change is mostly a wash, though it helps
    reduce stack size slightly. If we really care about supporting
    256-bit mappings though, we should consider rewriting some of this
    code to avoid keeping and assigning so many 256-bit objects on the
    stack.]
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
This commit is contained in:
Arnd Bergmann 2016-02-29 13:20:28 +01:00 committed by Brian Norris
parent 20c07a5bf0
commit fddcca5107
2 changed files with 8 additions and 12 deletions
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1
drivers/mtd/chips/Kconfig
View File

@ -115,6 +115,7 @@ config MTD_MAP_BANK_WIDTH_16
config MTD_MAP_BANK_WIDTH_32
bool "Support 256-bit buswidth" if MTD_CFI_GEOMETRY
select MTD_COMPLEX_MAPPINGS if HAS_IOMEM
default n
help
If you wish to support CFI devices on a physical bus which is

7
include/linux/mtd/map.h
View File

@ -122,18 +122,13 @@
#endif
#ifdef CONFIG_MTD_MAP_BANK_WIDTH_32
# ifdef map_bankwidth
/* always use indirect access for 256-bit to preserve kernel stack */
# undef map_bankwidth
# define map_bankwidth(map) ((map)->bankwidth)
# undef map_bankwidth_is_large
# define map_bankwidth_is_large(map) (map_bankwidth(map) > BITS_PER_LONG/8)
# undef map_words
# define map_words(map) map_calc_words(map)
# else
# define map_bankwidth(map) 32
# define map_bankwidth_is_large(map) (1)
# define map_words(map) map_calc_words(map)
# endif
#define map_bankwidth_is_32(map) (map_bankwidth(map) == 32)
#undef MAX_MAP_BANKWIDTH
#define MAX_MAP_BANKWIDTH 32