[illumos-Developer] Ugh... xdr_{float,double} problems

[Garrett D'Amore]

Ok, I'll backout the changes.  Can you please file a bug?  I probably 
won't get around to backing this change out until tonight as I'm 
traveling and on limited battery power.

     - Garrett

On 01/28/11 08:48 AM, Jason King wrote:
> After lengthy discussions, and even more digging... it looks like
> there's a bit of a very-long standing mess with the C xdr API.
>
> The problem is, the OTW XDR format for 32&  64 bit doubles is
> identical on x86, amd64, sparc, and sparcv9.  In theory, the code
> should then just merely copy the values out unchanged.
> However, that really happened was on little-endian platforms, the byte
> values for fp values were being (incorrectly) byteswapped by the
> library.  Instead of fixing the library, it appears the existing
> software that actually uses fp with xdr workaround the bug on those
> platforms.  Of course the recent putback broke the workaround.
>
> Essentially:
>
> 1. code is released with broken xdr_{float,double}
> 2. code is written w/ workarounds
> 3. code is updated, and __amd64 define is (incorrectly) changed to
> amd64.  This causes xdr_{float,double} to revert to a slower, platform
> independent version that correctly (minus rouding errors) writes the
> value into the stream (without swapping).
> 4. My fix correctly writes fp values unchanged to XDR stream, but also
> breaks any software with workarounds.  The test cases were written to
> the RFC&  man pages (since I couldn't really find anything out there
> that uses
>
> Given the pervasiveness of this, we probably need to do something similar to:
>
> 1. Revert the behavior to the traditional broken behavior
> 2. Update the man pages to document this behavior
> 3. Add a #define to the rpc/xdr.h header file (XDR_FLOAT_NO_SWAP ?) to
> allow applications to select the correct behavior when defined (and
> document this in the manpage).
>
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