On 2024/8/23 09:25, Dmitry Torokhov wrote: > On Fri, Aug 23, 2024 at 09:14:12AM +0800, Greg Kroah-Hartman wrote: >> On Fri, Aug 23, 2024 at 08:46:12AM +0800, Zijun Hu wrote: >>> On 2024/8/23 08:02, Dmitry Torokhov wrote: >>>> Hi, >>>> >>>> On Fri, Aug 23, 2024 at 07:46:09AM +0800, Zijun Hu wrote: >>>>> From: Zijun Hu <quic_zijuhu@xxxxxxxxxxx> >>>>> >>>>> An uninitialized variable @data.have_async may be used as analyzed >>>>> by the following inline comments: >>>>> >>>>> static int __device_attach(struct device *dev, bool allow_async) >>>>> { >>>>> // if @allow_async is true. >>>>> >>>>> ... >>>>> struct device_attach_data data = { >>>>> .dev = dev, >>>>> .check_async = allow_async, >>>>> .want_async = false, >>>>> }; >>>>> // @data.have_async is not initialized. >>>> >>>> No, in the presence of a structure initializer fields not explicitly >>>> initialized will be set to 0 by the compiler. >>>> >>> really? >>> do all C compilers have such behavior ? >> >> Oh wait, if this were static, then yes, it would all be set to 0, sorry, >> I misread this. >> >> This is on the stack so it needs to be zeroed out explicitly. We should >> set the whole thing to 0 and then set only the fields we want to >> override to ensure it's all correct. > > No we do not. ISO/IEC 9899:201x 6.7.9 Initialization: > > "21 If there are fewer initializers in a brace-enclosed list than there > are elements or members of an aggregate, or fewer characters in a string > literal used to initialize an array of known size than there are > elements in the array, the remainder of the aggregate shall be > initialized implicitly the same as objects that have static storage > duration." > > That is why you can 0-initialize a structure by doing: > > struct s s1 = { 0 }; > > or even > > struct s s1 = { }; > For above both initialization: it appears to initialize the whole struct. but For the initialization approach we discuss, it appears to initialize partial struct, it is easy to mislead developers. > Thanks. >