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From: Alistair Francis <alistair23@gmail.com>
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To: qemu-devel@nongnu.org
Cc: alistair23@gmail.com, Nikita Shubin <n.shubin@yadro.com>,
Alistair Francis <alistair.francis@wdc.com>
Subject: [PULL v2 45/45] target/riscv: don't read CSR in riscv_csrrw_do64
Date: Mon, 11 Sep 2023 16:43:20 +1000
Message-ID: <20230911064320.939791-46-alistair.francis@wdc.com>
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From: Nikita Shubin <n.shubin@yadro.com>
As per ISA:
"For CSRRWI, if rd=3Dx0, then the instruction shall not read the CSR and
shall not cause any of the side effects that might occur on a CSR read."
trans_csrrwi() and trans_csrrw() call do_csrw() if rd=3Dx0, do_csrw() calls
riscv_csrrw_do64(), via helper_csrw() passing NULL as *ret_value.
Signed-off-by: Nikita Shubin <n.shubin@yadro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20230808090914.17634-1-nikita.shubin@maquefel.me>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
---
target/riscv/csr.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 68eecc3c96..85a31dc420 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -3917,21 +3917,27 @@ static RISCVException riscv_csrrw_do64(CPURISCVStat=
e *env, int csrno,
target_ulong write_mask)
{
RISCVException ret;
- target_ulong old_value;
+ target_ulong old_value =3D 0;
=20
/* 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_m=
ask);
}
=20
- /* if no accessor exists then return failure */
- if (!csr_ops[csrno].read) {
- return RISCV_EXCP_ILLEGAL_INST;
- }
- /* read old value */
- ret =3D csr_ops[csrno].read(env, csrno, &old_value);
- if (ret !=3D RISCV_EXCP_NONE) {
- return ret;
+ /*
+ * ret_value =3D=3D NULL means that rd=3Dx0 and we're coming from help=
er_csrw()
+ * and we can't throw side effects caused by CSR reads.
+ */
+ if (ret_value) {
+ /* if no accessor exists then return failure */
+ if (!csr_ops[csrno].read) {
+ return RISCV_EXCP_ILLEGAL_INST;
+ }
+ /* read old value */
+ ret =3D csr_ops[csrno].read(env, csrno, &old_value);
+ if (ret !=3D RISCV_EXCP_NONE) {
+ return ret;
+ }
}
=20
/* write value if writable and write mask set, otherwise drop writes */
--=20
2.41.0