[v1] target/riscv: mask vxrm csrw write to the low 2 bits

[PATCH] target/riscv: mask vxrm csrw write to the low 2 bits

Abhigyan Kumar posted 1 patch 12 hours ago

Diff against v2
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Patches applied successfully (tree, apply log)
git fetch https://github.com/patchew-project/qemu tags/patchew/20260530042657.844880-1-314abh@gmail.com

Maintainers: Palmer Dabbelt <palmer@dabbelt.com>, Alistair Francis <alistair.francis@wdc.com>, Weiwei Li <liwei1518@gmail.com>, Daniel Henrique Barboza <daniel.barboza@oss.qualcomm.com>, Liu Zhiwei <zhiwei_liu@linux.alibaba.com>, Chao Liu <chao.liu.zevorn@gmail.com>

There is a newer version of this series

target/riscv/csr.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

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[PATCH] target/riscv: mask vxrm csrw write to the low 2 bits

Posted by Abhigyan Kumar 12 hours ago

Citing the RISC-V specification:

    "The vector fixed-point rounding-mode register holds a two-bit
    read-write rounding-mode field in the least-significant bits
    (vxrm[1:0]). The upper bits, vxrm[XLEN-1:2], should be written as
    zeros."

QEMU wrote full value into env->vxrm causing read of upper bits too. The
2-bit mask has been added with this change to prevent it.

Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3470
Signed-off-by: Abhigyan Kumar <314abh@gmail.com>
---
 target/riscv/csr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index 5514e0f45..f5b0895fd 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -977,7 +977,7 @@ static RISCVException write_vxrm(CPURISCVState *env, int csrno,
 #if !defined(CONFIG_USER_ONLY)
     env->mstatus |= MSTATUS_VS;
 #endif
-    env->vxrm = val;
+    env->vxrm = val & 0x03;
     return RISCV_EXCP_NONE;
 }
 
-- 
2.54.0