Re: [Qemu-devel] [PATCH] tcg/mips: Bugfix for crash when running program with qemu-i386.

[Richard Henderson]

On 07/06/2017 05:15 PM, Jiang Biao wrote:
> When running a helloworld program with qemu-i386 in linux-user
> mode on Loongson 3A3000, it will crash. This patch fix the bug.
>
> Signed-off-by: Jiang Biao<address@hidden>
> ---
>   tcg/mips/tcg-target.inc.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tcg/mips/tcg-target.inc.c b/tcg/mips/tcg-target.inc.c
> index 8cff9a6..e6fedc9 100644
> --- a/tcg/mips/tcg-target.inc.c
> +++ b/tcg/mips/tcg-target.inc.c
> @@ -1540,7 +1540,7 @@ static void tcg_out_qemu_ld(TCGContext *s, const TCGArg 
> *args, bool is_64)
>   #else
>       if (TCG_TARGET_REG_BITS > TARGET_LONG_BITS) {
>           tcg_out_ext32u(s, base, addr_regl);
> -        addr_regl = base;
> +        tcg_out_mov(s, TCG_TYPE_PTR, addr_regl, base);
>       }
>       if (guest_base == 0 && data_regl != addr_regl) {
>           base = addr_regl;

This is wrong, because you're not allowed to modify the input operands.

Try this, just a few lines lower in the function:

-        tcg_out_movi(s, TCG_TYPE_PTR, base, guest_base);
-        tcg_out_opc_reg(s, ALIAS_PADD, base, base, addr_regl);
+        tcg_out_movi(s, TCG_TYPE_PTR, TCG_TMP0, guest_base);
+        tcg_out_opc_reg(s, ALIAS_PADD, base, TCG_TMP0, addr_regl);

and you'll need the same change within tcg_out_qemu_st.

Better would be to reserve a register for the guest_base, like we do for ppc. 
See all of the uses of TCG_GUEST_BASE_REG in tcg/ppc/tcg-target.inc.c.


r~