Teach Sstc to respect xenvcfg.STCE #1591
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Please change the title and commit message to describe what is changing. Explain in the PR what was wrong with the old code, an example of how it could misbehave, and how this fixes it.
I guess the old code is only problematic if --isa=Sstc is enabled? But it's not clear.
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Add additional paragraphs in the commit message to describe an example of misbehaving and the solution's strategy. The title was a shortened, one-sentence summary from the spec, which the commit aims to conform to. |
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How about this title: Followed by the explanation of the problem. The last paragraph in 15cd07d is unnecessary because it's simply describing the implementation which is already easy to understand from the diff. |
When menvcfg.STCE=0, mip.STIP reverts to its defined behavior as if unsupporting Sstc extension. When henvcfg.STCE=0, mip.VSTIP reverts to its defined behavior as if unsupporting Sstc extension. [riscvarchive/riscv-time-compare#5] The previous Sstc implementation does not respect the xenvcfg.STCE. In other words, the Sstc may assert mip.STIP (mip.VSTIP) when menvcfg.STCE=0 (henvcfg.STCE=0), which is a misbehaving.
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When menvcfg.STCE=0, mip.STIP reverts to its defined behavior as if unsupporting Sstc extension. When henvcfg.STCE=0, mip.VSTIP reverts to its defined behavior as if unsupporting Sstc extension.
Reference: riscvarchive/riscv-time-compare#5