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[PATCH v3 1/3] target/riscv: Fix tb->flags FS status

From: shihpo . hung
Subject: [PATCH v3 1/3] target/riscv: Fix tb->flags FS status
Date: Tue, 14 Jan 2020 22:17:31 -0800

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:

Thanks to Richard for pointing out the actual bug.

v3: remove the redundant condition
v2: root cause FS problem

Suggested-by: Richard Henderson <address@hidden>
Signed-off-by: ShihPo Hung <address@hidden>
Reviewed-by: Richard Henderson <address@hidden>
 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 e59343e..de0a8d8 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,
     *flags = TB_FLAGS_MSTATUS_FS;
-    *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);

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