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riscv: preserve fflags when rejecting a reserved frm value #280

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Merged
LekKit merged 2 commits into from
Sep 22, 2026
Merged

riscv: preserve fflags when rejecting a reserved frm value #280

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3021d72
riscv: preserve fflags for reserved frm writes
Sep 6, 2026
a529854
riscv: clarify invalid frm handling
Sep 22, 2026
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6 changes: 3 additions & 3 deletions src/cpu/riscv_csr.c
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Original file line number Diff line number Diff line change
Expand Up @@ -425,8 +425,8 @@ static void riscv_update_fcsr(rvvm_hart_t* vm, uint32_t old_fcsr, uint32_t new_f
uint32_t new_fflags = bit_cut(new_fcsr, 0, 5);
if (unlikely(new_frm != old_frm)) {
if (new_frm > RM_RMM) {
// Invalid rounding mode written
return;
// Ignore invalid frm, apply other fcsr fields
new_frm = old_frm;
} else {
// Set host rounding mode
fpu_set_rounding_mode(new_frm);
Expand All @@ -438,7 +438,7 @@ static void riscv_update_fcsr(rvvm_hart_t* vm, uint32_t old_fcsr, uint32_t new_f
fpu_set_exceptions(0);
}
}
vm->csr.fcsr = new_fcsr;
vm->csr.fcsr = new_fflags | (new_frm << 5);
}
}

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