[ECOS] Re: uSTL hello world
Fri Sep 11 19:25:00 GMT 2009
>>>>> "Jifl" == Jonathan Larmour <email@example.com> writes:
>> Jifl, is there a preferred way to ensure initialisation of the
>> stdio streams in the file descriptor table? I note that open()
>> in the file I/O package uses:
>> Is this addressing the same issue that we're observing with
Jifl> I think there's a more fundamental problem, not specific to
Jifl> uSTL (so I think Uwe's workaround isn't really appropriate).
Jifl> That is that something like:
Jifl> write(STDOUT_FILENO, buf, n);
Jifl> can't be guaranteed to just work, at present. That's a bug.
Jifl> I think those CYG_REFERENCE_OBJECT lines (and surrounding
Jifl> ifdef) need to move out of open() and into cyg_fd_init().
Jifl> Theoretically cyg_fp_get() would be slightly better, but
Jifl> that is called a lot, and there is a trivial but non-zero
Jifl> overhead to CYG_REFERENCE_OBJECT. I'd appreciate Nick's
Jifl> opinion on this proposal if possible though. It does mean
Jifl> that including the fileio package at all in a configuration
Jifl> would then guarantee pulling in stdin/stdout/stderr, even
Jifl> irrespective of use. Maybe the number of people this would
Jifl> affect is too small to care about. Maybe there should be a
Jifl> default-enabled option, to allow it to be turned off to
Jifl> remove that dependency.
Jifl> Taking the usual principle of "leave it to the user", I
Jifl> think I'd personally lean towards the latter.
I think there is another approach which might fit in better with
linker garbage collection. Instead of #define'ing STDOUT_FILENO as 1,
declare it as an extern const char. Then provide the variable
STDOUT_FILENO in some module which causes the necessary initialization
to happen. It is slightly more expensive: a bit of space for the const
variable, an extra memory access for the write() call. However it
would eliminate the need for CYG_REFERENCE_OBJECT's and it would allow
linker garbage collection to work as normal.
Obviously code which uses write(1, buf, n) would still be broken, and
requires that STDOUT_FILENO be defined as 1. Hence my proposal would
not be fully standards-compliant.
Bart Veer eCos Configuration Architect
eCosCentric Limited The eCos experts http://www.ecoscentric.com/
Barnwell House, Barnwell Drive, Cambridge, UK. Tel: +44 1223 245571
Registered in England and Wales: Reg No 4422071.
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