From: Nikita Shubin <n.shubin@yadro.com>
In case of write-only CSR don't return illegal inst error when CSR is
written and lacks read op.
Signed-off-by: Nikita Shubin <n.shubin@yadro.com>
---
Anyway it not might be a good idea to read CSR when we are not asked
for, during CSRRW or CSRRWI:
"For CSRRWI, if rd=x0, then the instruction shall not read the CSR and
shall not cause any of the side effects that might occur on a CSR read."
May be i am missing something of course.
---
target/riscv/csr.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index ea7585329e..6d6a8821a8 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3915,14 +3915,17 @@ static RISCVException riscv_csrrw_do64(CPURISCVState *env, int csrno,
return csr_ops[csrno].op(env, csrno, ret_value, new_value, write_mask);
}
- /* if no accessor exists then return failure */
- if (!csr_ops[csrno].read) {
- return RISCV_EXCP_ILLEGAL_INST;
- }
- /* read old value */
- ret = csr_ops[csrno].read(env, csrno, &old_value);
- if (ret != RISCV_EXCP_NONE) {
- return ret;
+ /* don't read if ret_value==NULL */
+ if (ret_value) {
+ /* if no accessor exists then return failure */
+ if (!csr_ops[csrno].read) {
+ return RISCV_EXCP_ILLEGAL_INST;
+ }
+ /* read old value */
+ ret = csr_ops[csrno].read(env, csrno, &old_value);
+ if (ret != RISCV_EXCP_NONE) {
+ return ret;
+ }
}
/* write value if writable and write mask set, otherwise drop writes */
--
2.39.2