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Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.
From: |
Peter Maydell |
Subject: |
Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11 |
Date: |
Fri, 6 Apr 2018 17:16:44 +0100 |
On 6 April 2018 at 15:51, Peter Maydell <address@hidden> wrote:
> On 6 April 2018 at 14:33, Peter Maydell <address@hidden> wrote:
>> On this end I should try this with a 32-bit Linux host.
>
> I've now done this, and can reproduce the problem. So the
> issue is generic to 32-bit hosts.
>
> I'll see if I can figure out what's going wrong.
I've tracked down the issue -- it is with the arm frontend's
handling of the tcg_insn_start parameters. Specifically, we
have a 3-operand tcg_insn_start:
tcg_gen_insn_start(dc->pc,
(dc->condexec_cond << 4) | (dc->condexec_mask >> 1),
0);
dc->insn_start = tcg_last_op();
where we patch in the 3rd operand later sometimes in
disas_set_insn_syndrome():
tcg_set_insn_param(s->insn_start, 2, syn);
Unfortunately, if we're running on a setup where
TARGET_LONG_BITS > TCG_TARGET_REG_BITS (ie 32 bit guest
on 64 bit host), tcg_gen_insn_start() has under the hood
split the 3 operands we gave it into 6, and so we end
up patching the wrong one.
The effect is that the first time the icount code needs to
call io_recompile, we set condexec_bits to a bogus value
which is also too big for its space in tb_flags and the
CPSR, and execution starts to diverge from there onward.
The following change fixes this:
diff --git a/target/arm/translate.h b/target/arm/translate.h
index c47febf99d..f04ece9cfd 100644
--- a/target/arm/translate.h
+++ b/target/arm/translate.h
@@ -120,7 +120,15 @@ static inline void
disas_set_insn_syndrome(DisasContext *s, uint32_t syn)
/* We check and clear insn_start_idx to catch multiple updates. */
assert(s->insn_start != NULL);
+#if TARGET_LONG_BITS <= TCG_TARGET_REG_BITS
tcg_set_insn_param(s->insn_start, 2, syn);
+#else
+ /* tcg_gen_insn_start has split every target_ulong argument to
+ * op_insn_start into two 32-bit arguments, so we want the low
+ * half of the 3rd input argument, which is at index 4.
+ */
+ tcg_set_insn_param(s->insn_start, 4, syn);
+#endif
s->insn_start = NULL;
}
but I'm not convinced it's the neatest way to do it.
Nobody else plays this game with tcg_set_insn_param() (except
icount, which doesn't do it with target_ulong sized values),
so this bug is specific to the arm target.
Richard: do you have a cleaner suggestion than throwing this
ifdef into the arm code?
thanks
-- PMM
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Peter Maydell, 2018/04/05
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, alarson, 2018/04/05
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Peter Maydell, 2018/04/05
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, alarson, 2018/04/05
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Peter Maydell, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Stefan Weil, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, alarson, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Peter Maydell, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Peter Maydell, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11,
Peter Maydell <=
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, alarson, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Peter Maydell, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, alarson, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, Mark Cave-Ayland, 2018/04/06
- Re: [Qemu-devel] -icount changes physical address assignments in QEMU 2.10/2.11, alarson, 2018/04/06