From: ShihPo Hung <shihpo.hung@sifive.com>

Date: Tue, 14 Jan 2020 22:17:31 -0800

Subject: [PATCH] target/riscv: Fix tb->flags FS status

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.

In current implementation tb->flags merges all non-disabled state to

dirty. This means the code in mark_fs_dirty in translate.c that

handles initial and clean states is unreachable.

This patch fixes it and is successfully tested with:

  libquantum

Thanks to Richard for pointing out the actual bug.

v3: remove the redundant condition

v2: root cause FS problem

Suggested-by: Richard Henderson <richard.henderson@linaro.org>

Signed-off-by: ShihPo Hung <shihpo.hung@sifive.com>

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

---

 target/riscv/cpu.h | 5 +----

 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/target/riscv/cpu.h b/target/riscv/cpu.h

index e59343e13c..de0a8d893a 100644

--- a/target/riscv/cpu.h

+++ b/target/riscv/cpu.h

@@ -293,10 +293,7 @@ static inline void cpu_get_tb_cpu_state(CPURISCVState *env, target_ulong *pc,

 #ifdef CONFIG_USER_ONLY

     *flags = TB_FLAGS_MSTATUS_FS;

 #else

-    *flags = cpu_mmu_index(env, 0);

-    if (riscv_cpu_fp_enabled(env)) {

-        *flags |= TB_FLAGS_MSTATUS_FS;

-    }

+    *flags = cpu_mmu_index(env, 0) | (env->mstatus & MSTATUS_FS);

 #endif

 }