[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [PATCH v2 17/22] tcg/ppc: Reorg goto_tb implementation
From: |
Alex Bennée |
Subject: |
Re: [PATCH v2 17/22] tcg/ppc: Reorg goto_tb implementation |
Date: |
Tue, 17 Jan 2023 18:30:13 +0000 |
User-agent: |
mu4e 1.9.15; emacs 29.0.60 |
Richard Henderson <richard.henderson@linaro.org> writes:
> The old ppc64 implementation replaces 2 or 4 insns, which leaves a race
> condition in which a thread could be stopped at a PC in the middle of
> the sequence, and when restarted does not see the complete address
> computation and branches to nowhere.
>
> The new implemetation replaces only one insn, swapping between
>
> b <dest>
> and
> mtctr r31
>
> falling through to a general-case indirect branch.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
<snip>
>
> static void tcg_out_goto_tb(TCGContext *s, int which)
> {
> - /* Direct jump. */
> - if (TCG_TARGET_REG_BITS == 64) {
> - /* Ensure the next insns are 8 or 16-byte aligned. */
> - while ((uintptr_t)s->code_ptr & (have_isa_2_07 ? 15 : 7)) {
> - tcg_out32(s, NOP);
> - }
> + uintptr_t ptr = get_jmp_target_addr(s, which);
> +
> + if (USE_REG_TB) {
> + ptrdiff_t offset = tcg_tbrel_diff(s, (void *)ptr);
> + tcg_out_mem_long(s, LD, LDX, TCG_REG_TB, TCG_REG_TB, offset);
> +
> + /* Direct branch will be patched by tb_target_set_jmp_target. */
> set_jmp_insn_offset(s, which);
> - tcg_out32(s, ADDIS | TAI(TCG_REG_TB, TCG_REG_TB, 0));
> - tcg_out32(s, ADDI | TAI(TCG_REG_TB, TCG_REG_TB, 0));
> tcg_out32(s, MTSPR | RS(TCG_REG_TB) | CTR);
> +
> + /* When branch is out of range, fall through to indirect. */
> + tcg_out32(s, BCCTR | BO_ALWAYS);
> +
> + /* For the unlinked case, need to reset TCG_REG_TB. */
> + set_jmp_reset_offset(s, which);
> + tcg_out_mem_long(s, ADDI, ADD, TCG_REG_TB, TCG_REG_TB,
> + -tcg_current_code_size(s));
> + } else {
> + /* Direct branch will be patched by tb_target_set_jmp_target. */
> + set_jmp_insn_offset(s, which);
> + tcg_out32(s, NOP);
> +
> + /* When branch is out of range, fall through to indirect. */
> + tcg_out_movi(s, TCG_TYPE_PTR, TCG_REG_TMP1, ptr - (int16_t)ptr);
> + tcg_out_ld(s, TCG_TYPE_PTR, TCG_REG_TMP1, TCG_REG_TMP1,
> (int16_t)ptr);
> + tcg_out32(s, MTSPR | RS(TCG_REG_TMP1) | CTR);
> tcg_out32(s, BCCTR | BO_ALWAYS);
> set_jmp_reset_offset(s, which);
> - if (USE_REG_TB) {
> - /* For the unlinked case, need to reset TCG_REG_TB. */
> - tcg_out_mem_long(s, ADDI, ADD, TCG_REG_TB, TCG_REG_TB,
> - -tcg_current_code_size(s));
> - }
> - } else {
> - set_jmp_insn_offset(s, which);
> - tcg_out32(s, B);
> - set_jmp_reset_offset(s, 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 diff = addr - jmp_rx;
> + tcg_insn_unit insn;
> +
> + if (in_range_b(diff)) {
> + insn = B | (diff & 0x3fffffc);
Again deposit would be nice here.
> + } else if (USE_REG_TB) {
> + insn = MTSPR | RS(TCG_REG_TB) | CTR;
> + } else {
> + insn = NOP;
> + }
> +
> + qatomic_set((uint32_t *)jmp_rw, insn);
> + flush_idcache_range(jmp_rx, jmp_rw, 4);
> +}
> +
> static void tcg_out_op(TCGContext *s, TCGOpcode opc,
> const TCGArg args[TCG_MAX_OP_ARGS],
> const int const_args[TCG_MAX_OP_ARGS])
Otherwise:
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
- Re: [PATCH v2 12/22] tcg: Change tb_target_set_jmp_target arguments, (continued)
- [PATCH v2 14/22] tcg: Always define tb_target_set_jmp_target, Richard Henderson, 2023/01/08
- [PATCH v2 15/22] tcg: Remove TCG_TARGET_HAS_direct_jump, Richard Henderson, 2023/01/08
- [PATCH v2 13/22] tcg: Move tb_target_set_jmp_target declaration to tcg.h, Richard Henderson, 2023/01/08
- [PATCH v2 16/22] tcg/aarch64: Reorg goto_tb implementation, Richard Henderson, 2023/01/08
- [PATCH v2 17/22] tcg/ppc: Reorg goto_tb implementation, Richard Henderson, 2023/01/08
- Re: [PATCH v2 17/22] tcg/ppc: Reorg goto_tb implementation,
Alex Bennée <=
- [PATCH v2 18/22] tcg/sparc64: Remove USE_REG_TB, Richard Henderson, 2023/01/08
- [PATCH v2 19/22] tcg/sparc64: Reorg goto_tb implementation, Richard Henderson, 2023/01/08
- [PATCH v2 20/22] tcg/arm: Implement direct branch for goto_tb, Richard Henderson, 2023/01/08
- [PATCH v2 21/22] tcg/riscv: Introduce OPC_NOP, Richard Henderson, 2023/01/08
- [PATCH v2 22/22] tcg/riscv: Implement direct branch for goto_tb, Richard Henderson, 2023/01/08