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Removing xtdc #519

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jrtc27 opened this issue Feb 4, 2025 · 1 comment · Fixed by #527
Closed

Removing xtdc #519

jrtc27 opened this issue Feb 4, 2025 · 1 comment · Fixed by #527

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@jrtc27
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jrtc27 commented Feb 4, 2025

As discussed in #503, it is believed that xtdc are not in fact required. sscratchc can be used to store whatever capability you need on entry to the kernel, and from there you can have any additional state you need stored. FreeBSD already uses it to store a pointer to per-CPU data when running in userspace, and so in CheriBSD we can extend it to also store DDC for hybrid kernels (implementation at CTSRD-CHERI/cheribsd@2178d40) rather than needing a separate register.

Does anyone have a reason why they believe xtdc should remain in the specification?
@andresag01
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It would be great to remove them! 👍

@andresag01 andresag01 mentioned this issue Feb 7, 2025
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tariqkurd-repo pushed a commit that referenced this issue Feb 7, 2025
@andresag01
Remove xtdc CSRs zcherihybrid extension (#527)
8f6682f 
Fixes #519
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Remove xtdc CSRs zcherihybrid extension andresag01/riscv-cheri
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@jrtc27 @andresag01