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scsi: libsas: Replace zero-length array with flexible-array

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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")

Link: https://lore.kernel.org/r/20200507192147.GA16206@embeddedor
Reviewed-by: John Garry <john.garry@huawei.com>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 14:21:47 -05:00 • committed by Martin K. Petersen
parent f9491ed56e
commit 00b42b70ae
2 changed files with 11 additions and 11 deletions
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8
include/scsi/sas.h
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@ -324,7 +324,7 @@ struct ssp_response_iu {
__be32 response_data_len;
u8 resp_data[0];
u8 sense_data[0];
u8 sense_data[];
} __attribute__ ((packed));
struct ssp_command_iu {
@ -346,7 +346,7 @@ struct ssp_command_iu {
u8 add_cdb_len:6;
u8 cdb[16];
u8 add_cdb[0];
u8 add_cdb[];
} __attribute__ ((packed));
struct xfer_rdy_iu {
@ -555,7 +555,7 @@ struct ssp_response_iu {
__be32 response_data_len;
u8 resp_data[0];
u8 sense_data[0];
u8 sense_data[];
} __attribute__ ((packed));
struct ssp_command_iu {
@ -577,7 +577,7 @@ struct ssp_command_iu {
u8 _r_c:2;
u8 cdb[16];
u8 add_cdb[0];
u8 add_cdb[];
} __attribute__ ((packed));
struct xfer_rdy_iu {