[ECOS] For GCCv3: recommend -fno-builtin and remove -fvtable-gc

[ECOS] For GCCv3: recommend -fno-builtin and remove -fvtable-gc

[Richard Shih-Ping Chan]

Hi eCos team - I would like to make two suggestions for GCC3

[1] Make -fno-builtin a default command line option.

This is to prevent unwanted optimisations of builtin functions
at the default optimisation level of -g -O2. An example is
the optimisation of printf and the consequent introduction of
extra symbols like putchar and puts by GCCv3.
This doesn't always link as some installs supply printf but not
putchar/puts. An example is the target+template pc+redboot. 
At -O2 GCCv3 really seems to convert
some printf to putchar/puts statements.

This should have no untoward effect on GCC2.95.


[2] -fvtable-gc is no longer supported by GCCv3 but I'm not sure
what implications that has.

Cheers
Richard Chan <cshihpin@dso.org.sg>

Re: [ECOS] For GCCv3: recommend -fno-builtin and remove -fvtable-gc

[Andrew Lunn]

On Tue, Jul 10, 2001 at 09:41:11AM -0800, Richard Shih-Ping Chan wrote:
> Hi eCos team - I would like to make two suggestions for GCC3
> 
> [1] Make -fno-builtin a default command line option.
> 
> This is to prevent unwanted optimisations of builtin functions
> at the default optimisation level of -g -O2. An example is
> the optimisation of printf and the consequent introduction of
> extra symbols like putchar and puts by GCCv3.

I don't think this is a good idea. Some of the build in functions are
optimized for the particular architecture, eg memcpy, memset,
etc. They will be faster than the equivelent in the eCos library.

Is there a -fno-builtin-printf command line option? Just turn off that
feature. The other option would be to rename printf in redboot, so the
optimizer does not recognise it.

        Andrew

Re: [ECOS] For GCCv3: recommend -fno-builtin and remove -fvtable-gc

[Jonathan Larmour]

Andrew Lunn wrote:
> 
> On Tue, Jul 10, 2001 at 09:41:11AM -0800, Richard Shih-Ping Chan wrote:
> > Hi eCos team - I would like to make two suggestions for GCC3
> >
> > [1] Make -fno-builtin a default command line option.
> >
> > This is to prevent unwanted optimisations of builtin functions
> > at the default optimisation level of -g -O2. An example is
> > the optimisation of printf and the consequent introduction of
> > extra symbols like putchar and puts by GCCv3.
> 
> I don't think this is a good idea. Some of the build in functions are
> optimized for the particular architecture, eg memcpy, memset,
> etc. They will be faster than the equivelent in the eCos library.
> 
> Is there a -fno-builtin-printf command line option? Just turn off that
> feature. The other option would be to rename printf in redboot, so the
> optimizer does not recognise it.

Yes we have plans to rename Redboot's printf, but in Redboot's short
lifetime it has already become quite pervasive.

In any case, we recommend avoiding GCC v3 on all targets where 2.95 support
exists. GCC v3 is not very stable for most embedded targets.

Jifl
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