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gcov: gcc_3_4: replace zero-length array with flexible-array member

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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]

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 <gustavo@embeddedor.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
Link: http://lkml.kernel.org/r/20200302224501.GA14175@embeddedor
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Gustavo A. R. Silva 2020-04-06 20:11:55 -07:00 committed by Linus Torvalds
parent fba4168ede
commit 7ff87182d1
1 changed files with 3 additions and 3 deletions
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6
kernel/gcov/gcc_3_4.c
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@ -38,7 +38,7 @@ static struct gcov_info *gcov_info_head;
struct gcov_fn_info { struct gcov_fn_info {
unsigned int ident; unsigned int ident;
unsigned int checksum; unsigned int checksum;
unsigned int n_ctrs[0]; unsigned int n_ctrs[];
}; };
/** /**
@ -78,7 +78,7 @@ struct gcov_info {
unsigned int n_functions; unsigned int n_functions;
const struct gcov_fn_info *functions; const struct gcov_fn_info *functions;
unsigned int ctr_mask; unsigned int ctr_mask;
struct gcov_ctr_info counts[0]; struct gcov_ctr_info counts[];
}; };
/** /**
@ -352,7 +352,7 @@ struct gcov_iterator {
unsigned int count; unsigned int count;
int num_types; int num_types;
struct type_info type_info[0]; struct type_info type_info[];
}; };
static struct gcov_fn_info *get_func(struct gcov_iterator *iter) static struct gcov_fn_info *get_func(struct gcov_iterator *iter)