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Re: [PATCH for-8.0] tcg/sparc64: Disable direct linking for goto_tb
From: |
Alex Bennée |
Subject: |
Re: [PATCH for-8.0] tcg/sparc64: Disable direct linking for goto_tb |
Date: |
Tue, 04 Apr 2023 16:32:14 +0100 |
User-agent: |
mu4e 1.10.0; emacs 29.0.60 |
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