On Fri, Jul 05, 2024 at 04:07:59PM +0200, Lukas Wunner wrote:
> On Fri, Jul 05, 2024 at 06:04:39AM -0700, Christoph Hellwig wrote:
> > > +struct dsm_output {
> > > + u16 status;
> > > + u8 function_specific_err;
> > > + u8 vendor_specific_err;
> > > + u32 state;
> > > +} __packed;
> >
> > This structure is naturally aligned, so no need for the __packed.
>
> Isn't the compiler free to insert padding wherever it sees fit?
In terms of the standard: yes. It could even reorder members. In
terms of not breaking the Linux kernel (or other low-level software)
left, right and center: no.
> structs passed to ACPI firmware would no longer comply with the
> spec-prescribed layout then and declaring them __packed seems to be
> the only way to ensure that doesn't happen.
Take a look at just about any driver, file system or network protocol.
