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mtd: Replace zero-length array with flexible-array 

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200507190033.GA15215@embeddedor
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 14:00:33 -05:00 committed by Vignesh Raghavendra
parent b359ed5184
commit 11399346ac
2 changed files with 4 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/mtd/cfi.h
View File

@ -138,7 +138,7 @@ struct cfi_ident {
uint16_t InterfaceDesc; uint16_t InterfaceDesc;
uint16_t MaxBufWriteSize; uint16_t MaxBufWriteSize;
uint8_t NumEraseRegions; uint8_t NumEraseRegions;
uint32_t EraseRegionInfo[0]; /* Not host ordered */ uint32_t EraseRegionInfo[]; /* Not host ordered */
} __packed; } __packed;
/* Extended Query Structure for both PRI and ALT */ /* Extended Query Structure for both PRI and ALT */
@ -165,7 +165,7 @@ struct cfi_pri_intelext {
uint16_t ProtRegAddr; uint16_t ProtRegAddr;
uint8_t FactProtRegSize; uint8_t FactProtRegSize;
uint8_t UserProtRegSize; uint8_t UserProtRegSize;
uint8_t extra[0]; uint8_t extra[];
} __packed; } __packed;
struct cfi_intelext_otpinfo { struct cfi_intelext_otpinfo {
@ -286,7 +286,7 @@ struct cfi_private {
map_word sector_erase_cmd; map_word sector_erase_cmd;
unsigned long chipshift; /* Because they're of the same type */ unsigned long chipshift; /* Because they're of the same type */
const char *im_name; /* inter_module name for cmdset_setup */ const char *im_name; /* inter_module name for cmdset_setup */
struct flchip chips[0]; /* per-chip data structure for each chip */ struct flchip chips[]; /* per-chip data structure for each chip */
}; };
uint32_t cfi_build_cmd_addr(uint32_t cmd_ofs, uint32_t cfi_build_cmd_addr(uint32_t cmd_ofs,

2
include/linux/mtd/qinfo.h
View File

@ -24,7 +24,7 @@ struct lpddr_private {
struct qinfo_chip *qinfo; struct qinfo_chip *qinfo;
int numchips; int numchips;
unsigned long chipshift; unsigned long chipshift;
struct flchip chips[0]; struct flchip chips[];
}; };
/* qinfo_query_info structure contains request information for /* qinfo_query_info structure contains request information for