Re: [PATCH v2] target/sh4: Fix TB_FLAG_UNALIGN

[Guenter Roeck]

On Sat, Dec 10, 2022 at 07:27:46AM -0800, Guenter Roeck wrote:
> Hi,
> 
> On Thu, Sep 01, 2022 at 11:15:09AM +0100, Richard Henderson wrote:
> > The value previously chosen overlaps GUSA_MASK.
> > 
> > Rename all DELAY_SLOT_* and GUSA_* defines to emphasize
> > that they are included in TB_FLAGs.  Add aliases for the
> > FPSCR and SR bits that are included in TB_FLAGS, so that
> > we don't accidentally reassign those bits.
> > 
> > Fixes: 4da06fb3062 ("target/sh4: Implement prctl_unalign_sigbus")
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/856
> > Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> 
> I noticed that my sh4 emulations crash randomly with qemu v7.2-rc4.
> This happens with all Linux kernel versions. Testing shows that this
> patch is responsible. Reverting it fixes the problem.
> 

The patch below fixes the problem for me.

Guenter

---
>From d488bcad383f360e522dbffe0d21f8ad39d33c61 Mon Sep 17 00:00:00 2001
From: Guenter Roeck <linux@roeck-us.net>
Date: Sun, 11 Dec 2022 14:14:47 -0800
Subject: [PATCH] target/sh4: Fix unaligned handling

Commit ab419fd8a035 ("target/sh4: Fix TB_FLAG_UNALIGN") made a number
of changes which seemed unrelated to the problem being fixed. In addition
to updating updating masks, it eliminated various mask operations.
This results in a number of inexplicable crashes, often associated
with alleged unaligned operations.

Improve alignment with the original code. Reintroduce mask operations,
and undo an added '#ifdef CONFIG_USER_ONLY'.

While I have no real idea what I am doing, the resulting code no longer
crashes, so it must do some good.

Fixes: ab419fd8a035 ("target/sh4: Fix TB_FLAG_UNALIGN")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
 linux-user/sh4/signal.c | 2 +-
 target/sh4/cpu.c        | 2 +-
 target/sh4/translate.c  | 2 --
 3 files changed, 2 insertions(+), 4 deletions(-)

diff --git a/linux-user/sh4/signal.c b/linux-user/sh4/signal.c
index c4ba962708..2135e2b881 100644
--- a/linux-user/sh4/signal.c
+++ b/linux-user/sh4/signal.c
@@ -161,7 +161,7 @@ static void restore_sigcontext(CPUSH4State *regs, struct 
target_sigcontext *sc)
     __get_user(regs->fpul, &sc->sc_fpul);
 
     regs->tra = -1;         /* disable syscall checks */
-    regs->flags = 0;
+    regs->flags &= ~(TB_FLAG_DELAY_SLOT_MASK | TB_FLAG_GUSA_MASK);
 }
 
 void setup_frame(int sig, struct target_sigaction *ka,
diff --git a/target/sh4/cpu.c b/target/sh4/cpu.c
index 453268392b..827cee25af 100644
--- a/target/sh4/cpu.c
+++ b/target/sh4/cpu.c
@@ -47,7 +47,7 @@ static void superh_cpu_synchronize_from_tb(CPUState *cs,
     SuperHCPU *cpu = SUPERH_CPU(cs);
 
     cpu->env.pc = tb_pc(tb);
-    cpu->env.flags = tb->flags;
+    cpu->env.flags = tb->flags & TB_FLAG_ENVFLAGS_MASK;
 }
 
 static void superh_restore_state_to_opc(CPUState *cs,
diff --git a/target/sh4/translate.c b/target/sh4/translate.c
index 7db3468b01..546c182463 100644
--- a/target/sh4/translate.c
+++ b/target/sh4/translate.c
@@ -2270,7 +2270,6 @@ static void sh4_tr_init_disas_context(DisasContextBase 
*dcbase, CPUState *cs)
                   (tbflags & (1 << SR_RB))) * 0x10;
     ctx->fbank = tbflags & FPSCR_FR ? 0x10 : 0;
 
-#ifdef CONFIG_USER_ONLY
     if (tbflags & TB_FLAG_GUSA_MASK) {
         /* In gUSA exclusive region. */
         uint32_t pc = ctx->base.pc_next;
@@ -2290,7 +2289,6 @@ static void sh4_tr_init_disas_context(DisasContextBase 
*dcbase, CPUState *cs)
             return;
         }
     }
-#endif
 
     /* Since the ISA is fixed-width, we can bound by the number
        of instructions remaining on the page.  */
-- 
2.36.2