Re: [Qemu-devel] [PATCH] tcg/aarch64: Fix tcg_out_qemu_{ld, st} for guest_base == 0

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/09/2015 22:07, Richard Henderson wrote:
> In ffc6372851d8631a9f9fa56ec613b3244dc635b9, we swapped the guest
> base to the address base register from the address index register.
> Except that 31 in the base slot is SP not XZR, so we need to be
> more intelligent about which reg gets placed in which slot.
> 
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Aurelien Jarno <aurelien@aurel32.net>
> Cc: Richard Henderson <rth@twiddle.net>
> Cc: qemu-stable@nongnu.org (v2.4.0)
> Reported-by: Andreas Färber <afaerber@suse.de>
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  tcg/aarch64/tcg-target.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/tcg/aarch64/tcg-target.c b/tcg/aarch64/tcg-target.c
> index 01ae610..0ed10a9 100644
> --- a/tcg/aarch64/tcg-target.c
> +++ b/tcg/aarch64/tcg-target.c
> @@ -56,6 +56,11 @@ static const int tcg_target_call_oarg_regs[1] = {
>  #define TCG_REG_TMP TCG_REG_X30
>  
>  #ifndef CONFIG_SOFTMMU
> +/* Note that XZR cannot be encoded in the address base register slot,
> +   as that actaully encodes SP.  So if we need to zero-extend the guest
> +   address, via the address index register slot, we need to load even
> +   a zero guest base into a register.  */
> +#define USE_GUEST_BASE     (guest_base != 0 || TARGET_LONG_BITS == 32)
>  #define TCG_REG_GUEST_BASE TCG_REG_X28
>  #endif
>  
> @@ -1224,9 +1229,13 @@ static void tcg_out_qemu_ld(TCGContext *s, TCGReg data_reg, TCGReg addr_reg,
>      add_qemu_ldst_label(s, true, oi, ext, data_reg, addr_reg,
>                          s->code_ptr, label_ptr);
>  #else /* !CONFIG_SOFTMMU */
> -    tcg_out_qemu_ld_direct(s, memop, ext, data_reg,
> -                           guest_base ? TCG_REG_GUEST_BASE : TCG_REG_XZR,
> -                           otype, addr_reg);
> +    if (USE_GUEST_BASE) {
> +        tcg_out_qemu_ld_direct(s, memop, ext, data_reg,
> +                               TCG_REG_GUEST_BASE, otype, addr_reg);
> +    } else {
> +        tcg_out_qemu_ld_direct(s, memop, ext, data_reg,
> +                               addr_reg, TCG_TYPE_I64, TCG_REG_XZR);
> +    }
>  #endif /* CONFIG_SOFTMMU */
>  }
>  
> @@ -1245,9 +1254,13 @@ static void tcg_out_qemu_st(TCGContext *s, TCGReg data_reg, TCGReg addr_reg,
>      add_qemu_ldst_label(s, false, oi, (memop & MO_SIZE)== MO_64,
>                          data_reg, addr_reg, s->code_ptr, label_ptr);
>  #else /* !CONFIG_SOFTMMU */
> -    tcg_out_qemu_st_direct(s, memop, data_reg,
> -                           guest_base ? TCG_REG_GUEST_BASE : TCG_REG_XZR,
> -                           otype, addr_reg);
> +    if (USE_GUEST_BASE) {
> +        tcg_out_qemu_st_direct(s, memop, data_reg,
> +                               TCG_REG_GUEST_BASE, otype, addr_reg);
> +    } else {
> +        tcg_out_qemu_st_direct(s, memop, data_reg,
> +                               addr_reg, TCG_TYPE_I64, TCG_REG_XZR);
> +    }
>  #endif /* CONFIG_SOFTMMU */
>  }
>  
> @@ -1806,7 +1819,7 @@ static void tcg_target_qemu_prologue(TCGContext *s)
>                    CPU_TEMP_BUF_NLONGS * sizeof(long));
>  
>  #if !defined(CONFIG_SOFTMMU)
> -    if (guest_base) {
> +    if (USE_GUEST_BASE) {
>          tcg_out_movi(s, TCG_TYPE_PTR, TCG_REG_GUEST_BASE, guest_base);
>          tcg_regset_set_reg(s->reserved_regs, TCG_REG_GUEST_BASE);
>      }
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>