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SubjectRe: reducing stack usage in v4l?
On Wed, 5 March 2003 07:34:37 -0800, Randy.Dunlap wrote:
> Russell King <> wrote:
> | On Wed, Mar 05, 2003 at 10:15:52AM +0100, Gerd Knorr wrote:
> | > Not sure what is the best idea to fix that. Don't like the kmalloc
> | > idea that much. The individual structs are not huge, the real problem
> | > is that many of them are allocated and only few are needed. Any
> | > chance to tell gcc that it should allocate block-local variables at
> | > the start block not at the start of the function?
> |
> | Not a particularly clean idea, but maybe creating a union of the
> | structures and putting that on the stack? (ie, doing what GCC should
> | be doing in the first place.)
> That's an idea. Or make separate called functions for each ioctl and declare
> the structures inside them?

As far as I have seen, at least ds_ioctl uses the union trick. And the
three marked (*) ioctl-functions appear to be suffering from the same
gcc inability.

How much complaining is necessary for the gcc folks to worry about

0xc0ad420b <snd_emu10k1_fx8010_ioctl+3/5ec>: sub $0x814,%esp
0xc06dbd77 <v4l_compat_translate_ioctl+3/159c>: sub $0x804,%esp
0xc0521e43 <ida_ioctl+3/388>: sub $0x528,%esp
* 0xc01ed733 <presto_ioctl+3/13c4>: sub $0x4d0,%esp
* 0xc0bfbfd3 <br_ioctl_device+3/454>: sub $0x474,%esp
0xc07968bb <megadev_ioctl+3/c94>: sub $0x394,%esp
* 0xc068ff5b <ray_dev_ioctl+3/8b8>: sub $0x2e0,%esp
0xc0583a63 <netdev_ethtool_ioctl+3/e64>: sub $0x2c8,%esp
0xc0865963 <ds_ioctl+3/6b0>: sub $0x2ac,%esp
0xc04370c3 <vt_ioctl+3/1a84>: sub $0x29c,%esp
0xc054c5eb <e1000_ethtool_ioctl+3/6f8>: sub $0x290,%esp
0xc0299b23 <ncp_ioctl+3/13b0>: sub $0x278,%esp
0xc0532e67 <DAC960_UserIOCTL+3/17c0>: sub $0x230,%esp


Optimizations always bust things, because all optimizations are, in
the long haul, a form of cheating, and cheaters eventually get caught.
-- Larry Wall
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