riscv: keep mstatus.MPP=M after mret on harts without U-mode - #2396
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riscv: keep mstatus.MPP=M after mret on harts without U-mode#2396carlosqwqqwq wants to merge 2 commits into
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Thank you very much for taking the time to review this PR. We have rebased it onto dev and updated the mret MPP handling for harts without U-mode, with focused validation of the affected behavior. Could you please let us know what further code, test, or PR changes you would recommend? We will gladly adjust the patch to match the project guidelines. |
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Fixes #2391
Problem
helper_mretunconditionally writesmstatus.MPP = PRV_U. On a hart whose MISA does not include U, the least-privileged supported mode is M, so aftermretthe MPP field must read 3, not 0. The reproducer runs on a locally built no-U model library (defaultriscv_anywith RVU cleared; stock E51/U54 keep U as the control).Change
qemu/target/riscv/op_helper.chelper_mretselectsPRV_Uonly whenRVUis present andPRV_Motherwise. The focused unit test istest_riscv64_mret_without_uintests/unit/test_riscv.c.Validation
devand built the RISC-V targets.u034suite includes the U-clear profile patch and an explicit U-enabled control.Public reproducer and explicit profile setup:
https://github.com/carlosqwqqwq/unicorn-riscv-repros/tree/main/u034