Messages in this thread | | | Subject | Re: [PATCH] regulator: da9062: Replace zero-length array with flexible-array member | From | "Gustavo A. R. Silva" <> | Date | Wed, 12 Feb 2020 08:28:35 -0600 |
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On 2/12/20 05:12, Adam Thomson wrote: > On 11 February 2020 23:46, Gustavo A. R. Silva wrote: > >> 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 >> inadvertenly introduced[3] to the codebase from now on. >> >> 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 76497732932f ("cxgb3/l2t: Fix undefined behaviour") >> >> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com> >> --- >> drivers/regulator/da9062-regulator.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/regulator/da9062-regulator.c b/drivers/regulator/da9062- >> regulator.c >> index b064d8a19d4c..c3b6ba9bafdf 100644 >> --- a/drivers/regulator/da9062-regulator.c >> +++ b/drivers/regulator/da9062-regulator.c >> @@ -86,7 +86,7 @@ struct da9062_regulators { >> int irq_ldo_lim; >> unsigned n_regulators; >> /* Array size to be defined during init. Keep at end. */ >> - struct da9062_regulator regulator[0]; >> + struct da9062_regulator regulator[]; > > I don't think is the correct change here for this driver. In the probe > 'struct_size()' is used to determine the actual size requested from 'malloc()' > when allocating memory for this structure. It's not statically initialised. > Your change will break that code I believe. >
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]
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
Thanks -- Gustavo
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