qemu/0004-target-riscv-Fix-tb-flags-FS-status.patch

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
 }