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SubjectRe: [PATCH] USB: dummy-hcd: Fix uninitialized array use in init()
On Sat, Dec 05, 2020 at 10:15:11AM -0500, Alan Stern wrote:
> On Sat, Dec 05, 2020 at 07:47:01PM +0700, Minh Bùi Quang wrote:
> > Vào Th 6, 4 thg 12, 2020 vào lúc 23:12 Alan Stern
> > <stern@rowland.harvard.edu> đã viết:
> > > Does this initialization end up using less memory than an explicit
> > > memset() call?
> >
> > You mean speed?
>
> No, I mean memory space.
>
> A memset call requires a certain amount of instruction space (to push
> the arguments and make the call) but no static data space.
> Initialization requires some instruction space (to copy the data) and
> static data space as well (to hold the data that is to be copied).
>
> Alan Stern
>

Thank you for your clarification, I didn't think about it before.

As I check when compiling the code, with MAX_NUM_UDC=32 the initialization
becomes

xor eax,eax
mov ecx,0x40
rep stos DWORD PTR es:[rdi],eax

With MAX_NUM_UDC=2, the initialization becomes

mov QWORD PTR [rbp-0x30],0x0
mov QWORD PTR [rbp-0x28],0x0

As I see, initialization does not require additional static data space.
Am I right?

Thanks,
Quang Minh

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