structure packing on Linux

All,

I’m currently in discussion with a 3^rd party vendor about the correct packing of PKCS#11 structures.

Both the Word files (even latest v3.1 WD09) and the pkcs11.h header contain the information that structures should (header) / shall (Word) be 1-byte aligned.

The header file suggest to use #pragma pack for Windows, but says otherwise: “In a UNIX environment, you're on your own for this. You might not need to do (or be able to do!) anything.”

And in fact it seems on Linux nobody uses packing. There is a lengthy discussion about it on SoftHSM GitHub (https://github.com/opendnssec/SoftHSMv2/issues/471). pkcs11-logger is not packing (https://github.com/Pkcs11Interop/pkcs11-logger/blob/master/src/pkcs11-logger.h) and pkcs11-tool is not doing it (https://github.com/OpenSC/OpenSC/blob/master/src/pkcs11/pkcs11.h).

My assumption is this: the #pragma pack statement was introduced IMO in gcc 4.0 for MSVC compatibility reasons. This was in 2005. However, that time PKCS#11 was already at v2.20 and the same statement as above was included there. And IMO the only way to force packing in gcc was to add “__attribute__((packed))” to every declaration – which the TC did not want to do. And since it was not possible that time there was no packing. And for backwards compatibility reasons there is still none on Linux.

However, nowadays there is the #pragma pack and it would be easily possible. But this will affect compatibility vastly between providers and existing applications. But if application developers that are new to PKCS#11 take the standard seriously they will run into trouble. It depends on the function called. But C_GetInfo is certainly one of them…

So: Is there a need to reconsider these statements made in both the Word and header files?

What’s your opinion on this?

Regards,

Daniel

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