Re: [Qemu-devel] [RFC v1 16/23] riscv: tcg-target: Add slowpath load and store instructions

[Richard Henderson <richard.henderson@linaro.org>]

On 11/15/18 11:36 PM, Alistair Francis wrote:
> +static void tcg_out_mb(TCGContext *s, TCGArg a0)
> +{
> +    static const RISCVInsn fence[] = {
> +        [0 ... TCG_MO_ALL] = OPC_FENCE_RW_RW,
> +        [TCG_MO_LD_LD]     = OPC_FENCE_R_R,
> +        [TCG_MO_ST_LD]     = OPC_FENCE_W_R,
> +        [TCG_MO_LD_ST]     = OPC_FENCE_R_W,
> +        [TCG_MO_ST_ST]     = OPC_FENCE_W_W,
> +        [TCG_BAR_LDAQ]     = OPC_FENCE_R_RW,
> +        [TCG_BAR_STRL]     = OPC_FENCE_RW_W,
> +        [TCG_BAR_SC]       = OPC_FENCE_RW_RW,
> +    };
> +    tcg_out32(s, fence[a0 & TCG_MO_ALL]);
> +}
> +

TCG_MO_* and TCG_BAR_* are two different bitmasks, or'ed together.
Which you've separated by "& TCG_MO_ALL".  Thus the TCG_BAR_* constants should
not appear in this table.


> +static void * const qemu_ld_helpers[16] = {
> +    [MO_UB]   = helper_ret_ldub_mmu,
> +    [MO_SB]   = helper_ret_ldsb_mmu,
> +    [MO_LEUW] = helper_le_lduw_mmu,
> +    [MO_LESW] = helper_le_ldsw_mmu,
> +    [MO_LEUL] = helper_le_ldul_mmu,
> +    [MO_LESL] = helper_le_ldsl_mmu,
> +    [MO_LEQ]  = helper_le_ldq_mmu,
> +    [MO_BEUW] = helper_be_lduw_mmu,
> +    [MO_BESW] = helper_be_ldsw_mmu,
> +    [MO_BEUL] = helper_be_ldul_mmu,
> +    [MO_BESL] = helper_be_ldsl_mmu,
> +    [MO_BEQ]  = helper_be_ldq_mmu,
> +};

The LESL and BESL functions will not be present for rv32 -> link error.  Here
you do need an ifdef.

> +        } else {
> +            adj = cmp_off - sextract32(cmp_off, 0, 12);
> +            tcg_debug_assert(add_off - adj >= -0x1000
> +                             && add_off - adj < 0x1000);
> +
> +            tcg_out_opc_upper(s, OPC_LUI, base, adj);
> +            tcg_out_opc_reg(s, OPC_ADD, base, TCG_REG_ZERO, TCG_AREG0);

base, base, TCG_AREG0.

> +    /* Compare masked address with the TLB entry. */
> +    label_ptr[0] = s->code_ptr;
> +    tcg_out_opc_branch(s, OPC_BNE, TCG_REG_TMP0, TCG_REG_TMP1, 0);

Another case of a potential out-of-range branch.

It might be worthwhile to move all of this out-of-line from the start, where
that branch will always be short.  See

http://lists.nongnu.org/archive/html/qemu-devel/2018-11/msg02234.html


r~