Linux-kernel mailing list archive 2000-04,: Re: Preventing gcc from aligning stack???

# Re: Preventing gcc from aligning stack???

David Weinehall (tao@acc.umu.se)
Tue, 25 Jan 2000 20:06:12 +0100 (CET)

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On Tue, 25 Jan 2000, Jamie Lokier wrote:

> Tuukka Toivonen wrote:
> > > Yes it is. New gcc's (try to) keep the stack aligned at 16 bytes. The
> > > kernel stack is 8Kb on ia32; the 16byte alignment is mostly for floating
> > > point performance on Pentium and up, and floating point is forbidden in the
> >
> > I'd like to ask, why? Even double is only 8 bytes. Does this mean that 12
> > bytes is wasted each argumentless call and -fno-omit-frame-pointer, for
> > saving ebp?
>
> Yes. And gcc does tend to emit redundant stack alignment instructions
> too (though this is being improved).
>
> So turning off stack alignment reduces stack usage _and_ reduces the
> code size.

Oh, talking about alignment, how about anyone familiar with the inner
workings of gcc (2.7.2.3 in this case) tell me why I get this warning for
all newer v2.3.xx kernels:

sched.c:77: warning: alignment of `aligned_data' is greater than maximum
object file alignment
socket.c:182: warning: alignment of `sockets_in_use' is greater than
maximum object file alignment
irq.c:75: warning: alignment of `irq_desc' is greater than maximum object
file alignment
init_task.c:33: warning: alignment of `init_tss' is greater than maximum
object file alignment

Even if everything works fine, I *HATE* warnings.

/David Weinehall
_ _
// David Weinehall <tao@acc.umu.se> /> Northern lights wander \\
// Project MCA Linux hacker // Dance across the winter sky //
\> http://www.acc.umu.se/~tao/ </ Full colour fire </

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