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[PATCH v2] target/riscv: don't read write-only CSR
From: |
Nikita Shubin |
Subject: |
[PATCH v2] target/riscv: don't read write-only CSR |
Date: |
Thu, 27 Jul 2023 11:17:26 +0300 |
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>
---
Changelog:
- fixed uninitialized old_value
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 | 21 ++++++++++++---------
1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index ea7585329e..3f0b3277e4 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3908,21 +3908,24 @@ static RISCVException riscv_csrrw_do64(CPURISCVState
*env, int csrno,
target_ulong write_mask)
{
RISCVException ret;
- target_ulong old_value;
+ target_ulong old_value = 0;
/* execute combined read/write operation if it exists */
if (csr_ops[csrno].op) {
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
- [PATCH v2] target/riscv: don't read write-only CSR,
Nikita Shubin <=