Hi,

On Thu, 31 Jul 2025, Deepak Gupta wrote:

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vDSO related Opens (in the flux)

I am listing these opens for laying out plan and what to expect in future patch sets. And of course for the sake of discussion.

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How many vDSOs

Shadow stack instructions are carved out of zimop (may be operations) and if CPU doesn't implement zimop, they're illegal instructions. Kernel could be running on a CPU which may or may not implement zimop. And thus kernel will have to carry 2 different vDSOs and expose the appropriate one depending on whether CPU implements zimop or not.

If we merge this series without this, then when CFI is enabled in the Kconfig, we'll wind up with a non-portable kernel that won't run on older hardware. We go to great lengths to enable kernel binary portability across the presence or absence of other RISC-V extensions, and I think these CFI extensions should be no different.

So before considering this for merging, I'd like to see at least an attempt to implement the dual-vDSO approach (or something equivalent) where the same kernel binary with CFI enabled can run on both pre-Zimop and post-Zimop hardware, with the existing userspaces that are common today.

thanks Deepak,

- Paul