Re: [PATCH for-8.0] tcg/sparc64: Disable direct linking for goto_tb

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> Something is wrong with this code, and also wrong with gdb on the
> sparc systems to which I have access, so I cannot debug it either.
> Disable for now, so the release is not broken.

Why isn't this a revert then?

>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  tcg/sparc64/tcg-target.c.inc | 30 ++++--------------------------
>  1 file changed, 4 insertions(+), 26 deletions(-)
>
> diff --git a/tcg/sparc64/tcg-target.c.inc b/tcg/sparc64/tcg-target.c.inc
> index ccc4144f7c..694f2b9dd4 100644
> --- a/tcg/sparc64/tcg-target.c.inc
> +++ b/tcg/sparc64/tcg-target.c.inc
> @@ -1445,12 +1445,12 @@ static void tcg_out_goto_tb(TCGContext *s, int which)
>  {
>      ptrdiff_t off = tcg_tbrel_diff(s, (void *)get_jmp_target_addr(s, which));
>  
> -    /* Direct branch will be patched by tb_target_set_jmp_target. */
> +    /* Load link and indirect branch. */
>      set_jmp_insn_offset(s, which);
> -    tcg_out32(s, CALL);
> -    /* delay slot */
> -    tcg_debug_assert(check_fit_ptr(off, 13));
>      tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TB, TCG_REG_TB, off);
> +    tcg_out_arithi(s, TCG_REG_G0, TCG_REG_TB, 0, JMPL);
> +    /* delay slot */
> +    tcg_out_nop(s);
>      set_jmp_reset_offset(s, which);
>  
>      /*
> @@ -1469,28 +1469,6 @@ static void tcg_out_goto_tb(TCGContext *s, int which)
>  void tb_target_set_jmp_target(const TranslationBlock *tb, int n,
>                                uintptr_t jmp_rx, uintptr_t jmp_rw)
>  {
> -    uintptr_t addr = tb->jmp_target_addr[n];
> -    intptr_t br_disp = (intptr_t)(addr - jmp_rx) >> 2;
> -    tcg_insn_unit insn;
> -
> -    br_disp >>= 2;
> -    if (check_fit_ptr(br_disp, 19)) {
> -        /* ba,pt %icc, addr */
> -        insn = deposit32(INSN_OP(0) | INSN_OP2(1) | INSN_COND(COND_A)
> -                         | BPCC_ICC | BPCC_PT, 0, 19, br_disp);
> -    } else if (check_fit_ptr(br_disp, 22)) {
> -        /* ba addr */
> -        insn = deposit32(INSN_OP(0) | INSN_OP2(2) | INSN_COND(COND_A),
> -                         0, 22, br_disp);
> -    } else {
> -        /* The code_gen_buffer can't be larger than 2GB.  */
> -        tcg_debug_assert(check_fit_ptr(br_disp, 30));
> -        /* call addr */
> -        insn = deposit32(CALL, 0, 30, br_disp);
> -    }
> -
> -    qatomic_set((uint32_t *)jmp_rw, insn);
> -    flush_idcache_range(jmp_rx, jmp_rw, 4);

So the result it we never patch the jump so return to the main loop
after every block?

In so far this won't break anything else and I suspect you are one of
the last people who actually uses the backend:

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>


-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro