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remoteproc: 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>
Link: https://lore.kernel.org/r/20200507191943.GA16033@embeddedor
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 14:19:43 -05:00 committed by Bjorn Andersson
parent 8a226e2c71
commit 529798bae7
1 changed files with 3 additions and 3 deletions
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6
include/linux/remoteproc.h
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@ -73,7 +73,7 @@ struct resource_table {
u32 ver;
u32 num;
u32 reserved[2];
u32 offset[0];
u32 offset[];
} __packed;
/**
@ -87,7 +87,7 @@ struct resource_table {
*/
struct fw_rsc_hdr {
u32 type;
u8 data[0];
u8 data[];
} __packed;
/**
@ -306,7 +306,7 @@ struct fw_rsc_vdev {
u8 status;
u8 num_of_vrings;
u8 reserved[2];
struct fw_rsc_vdev_vring vring[0];
struct fw_rsc_vdev_vring vring[];
} __packed;
struct rproc;