[PATCH] target/riscv: Set mstatus.DS & FS correctly

[shihpo.hung@sifive.com]

It was found that running libquantum on riscv-linux qemu produced an
incorrect result. After investigation, FP registers are not saved
during context switch due to incorrect mstatus.FS.

Because ctx->mstatus_fs changes dynamically during runtime, we should
remove the mstatus_fs check at the translation stage.

Signed-off-by: ShihPo Hung <shihpo.hung@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Alistair Francis <Alistair.Francis@wdc.com>
Cc: Sagar Karandikar <sagark@eecs.berkeley.edu>
Cc: Bastian Koppelmann <kbastian@mail.uni-paderborn.de>
Cc: qemu-riscv@nongnu.org
---
 target/riscv/csr.c                      | 3 +--
 target/riscv/insn_trans/trans_rvd.inc.c | 1 -
 target/riscv/insn_trans/trans_rvf.inc.c | 1 -
 target/riscv/translate.c                | 6 +-----
 4 files changed, 2 insertions(+), 9 deletions(-)

diff --git a/target/riscv/csr.c b/target/riscv/csr.c
index da02f9f..0e34c29 100644
--- a/target/riscv/csr.c
+++ b/target/riscv/csr.c
@@ -341,8 +341,7 @@ static int write_mstatus(CPURISCVState *env, int csrno, target_ulong val)
 
     mstatus = (mstatus & ~mask) | (val & mask);
 
-    dirty = (riscv_cpu_fp_enabled(env) &&
-             ((mstatus & MSTATUS_FS) == MSTATUS_FS)) |
+    dirty = ((mstatus & MSTATUS_FS) == MSTATUS_FS) |
             ((mstatus & MSTATUS_XS) == MSTATUS_XS);
     mstatus = set_field(mstatus, MSTATUS_SD, dirty);
     env->mstatus = mstatus;
diff --git a/target/riscv/insn_trans/trans_rvd.inc.c b/target/riscv/insn_trans/trans_rvd.inc.c
index 393fa02..ea1044f 100644
--- a/target/riscv/insn_trans/trans_rvd.inc.c
+++ b/target/riscv/insn_trans/trans_rvd.inc.c
@@ -43,7 +43,6 @@ static bool trans_fsd(DisasContext *ctx, arg_fsd *a)
 
     tcg_gen_qemu_st_i64(cpu_fpr[a->rs2], t0, ctx->mem_idx, MO_TEQ);
 
-    mark_fs_dirty(ctx);
     tcg_temp_free(t0);
     return true;
 }
diff --git a/target/riscv/insn_trans/trans_rvf.inc.c b/target/riscv/insn_trans/trans_rvf.inc.c
index 172dbfa..e23cd63 100644
--- a/target/riscv/insn_trans/trans_rvf.inc.c
+++ b/target/riscv/insn_trans/trans_rvf.inc.c
@@ -52,7 +52,6 @@ static bool trans_fsw(DisasContext *ctx, arg_fsw *a)
     tcg_gen_qemu_st_i64(cpu_fpr[a->rs2], t0, ctx->mem_idx, MO_TEUL);
 
     tcg_temp_free(t0);
-    mark_fs_dirty(ctx);
     return true;
 }
 
diff --git a/target/riscv/translate.c b/target/riscv/translate.c
index ab6a891..4ef7300 100644
--- a/target/riscv/translate.c
+++ b/target/riscv/translate.c
@@ -386,15 +386,11 @@ static void gen_store_c(DisasContext *ctx, uint32_t opc, int rs1, int rs2,
 static void mark_fs_dirty(DisasContext *ctx)
 {
     TCGv tmp;
-    if (ctx->mstatus_fs == MSTATUS_FS) {
-        return;
-    }
-    /* Remember the state change for the rest of the TB.  */
-    ctx->mstatus_fs = MSTATUS_FS;
 
     tmp = tcg_temp_new();
     tcg_gen_ld_tl(tmp, cpu_env, offsetof(CPURISCVState, mstatus));
     tcg_gen_ori_tl(tmp, tmp, MSTATUS_FS);
+    tcg_gen_ori_tl(tmp, tmp, MSTATUS_SD);
     tcg_gen_st_tl(tmp, cpu_env, offsetof(CPURISCVState, mstatus));
     tcg_temp_free(tmp);
 }
-- 
2.7.4