Re: [Qemu-devel] [PATCH 1/2] tcg-arm: Implement tcg_register_jit

[li guang]

在 2013-06-05三的 05:49 -0700，Richard Henderson写道：
> On 06/04/2013 06:56 PM, li guang wrote:
> >> > +typedef struct {
> >> > +    uint32_t len __attribute__((aligned((sizeof(void *)))));
> >> > +    uint32_t cie_offset;
> >> > +    tcg_target_long func_start __attribute__((packed));
> >> > +    tcg_target_long func_len __attribute__((packed));
> > suspicious usage of packed attribute here,
> > since tcg_targe_long is either 32 or 64 bits,
> > not a struct or union.
> > 
> > Thanks!
> > 
> 
> Your question is worded poorly -- what has struct/union got to do with it?  
> One
> can adjust the alignment of any type.  Perhaps you don't know what it is that
> __attribute__((packed)) actually does?

referred from gcc manual:
"This attribute, attached to struct or union type definition, specifies
that each member (other than zero-width bitfields) of the structure or
union is placed to minimize the memory required."

so, what I mean is as the manual said, this attribute mostly applies to
struct or union.

> 
> While it's true that for ARM all four of these data members are 32-bit, and
> thus none of the attributes are required, it's not actually wrong.  Given that
> this sort of boiler-plate tends to get copied from target to target, and since
> the attributes *are* required for 64-bit hosts, 

forgive me if the question is fool,
packed means seize minimal memory size, right?
and any chance tcg_target_long smaller than 64 bits in
64-bit case?

> I prefer to keep all such
> structures defined similarly.
> 
> 
> r~