These fields are marked WARL (Write Any Values, Reads Legal Values) in the RISC-V Privileged Architecture Specification so instead of raising exceptions, illegal writes are silently dropped.
Cc: Sagar Karandikar <sag...@eecs.berkeley.edu> Cc: Bastian Koppelmann <kbast...@mail.uni-paderborn.de> Cc: Palmer Dabbelt <pal...@sifive.com> Cc: Alistair Francis <alistair.fran...@wdc.com> Signed-off-by: Michael Clark <m...@sifive.com> --- target/riscv/op_helper.c | 26 +++++++++++++------------- 1 file changed, 13 insertions(+), 13 deletions(-) diff --git a/target/riscv/op_helper.c b/target/riscv/op_helper.c index 828f20c..b81b9b6 100644 --- a/target/riscv/op_helper.c +++ b/target/riscv/op_helper.c @@ -213,17 +213,19 @@ void csr_write_helper(CPURISCVState *env, target_ulong val_to_write, break; } case CSR_MINSTRET: - qemu_log_mask(LOG_UNIMP, "CSR_MINSTRET: write not implemented"); - goto do_illegal; + /* minstret is WARL so unsupported writes are ignored */ + break; case CSR_MCYCLE: - qemu_log_mask(LOG_UNIMP, "CSR_MCYCLE: write not implemented"); - goto do_illegal; + /* mcycle is WARL so unsupported writes are ignored */ + break; +#if defined(TARGET_RISCV32) case CSR_MINSTRETH: - qemu_log_mask(LOG_UNIMP, "CSR_MINSTRETH: write not implemented"); - goto do_illegal; + /* minstreth is WARL so unsupported writes are ignored */ + break; case CSR_MCYCLEH: - qemu_log_mask(LOG_UNIMP, "CSR_MCYCLEH: write not implemented"); - goto do_illegal; + /* mcycleh is WARL so unsupported writes are ignored */ + break; +#endif case CSR_MUCOUNTEREN: env->mucounteren = val_to_write; break; @@ -314,10 +316,9 @@ void csr_write_helper(CPURISCVState *env, target_ulong val_to_write, case CSR_MBADADDR: env->mbadaddr = val_to_write; break; - case CSR_MISA: { - qemu_log_mask(LOG_UNIMP, "CSR_MISA: misa writes not supported"); - goto do_illegal; - } + case CSR_MISA: + /* misa is WARL so unsupported writes are ignored */ + break; case CSR_PMPCFG0: case CSR_PMPCFG1: case CSR_PMPCFG2: @@ -342,7 +343,6 @@ void csr_write_helper(CPURISCVState *env, target_ulong val_to_write, case CSR_PMPADDR15: pmpaddr_csr_write(env, csrno - CSR_PMPADDR0, val_to_write); break; - do_illegal: #endif default: do_raise_exception_err(env, RISCV_EXCP_ILLEGAL_INST, GETPC()); -- 2.7.0