tcg: Clarify thread safety check in tb_add_jump()
The check is to make sure that another thread hasn't already done the same while we were outside of tb_lock. Mention this in a comment. Signed-off-by: Sergey Fedorov <serge.fdrv@gmail.com> Signed-off-by: Sergey Fedorov <sergey.fedorov@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Richard Henderson <rth@twiddle.net>
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@ -372,20 +372,23 @@ static inline void tb_set_jmp_target(TranslationBlock *tb,
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static inline void tb_add_jump(TranslationBlock *tb, int n,
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TranslationBlock *tb_next)
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{
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/* NOTE: this test is only needed for thread safety */
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if (!tb->jmp_list_next[n]) {
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qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc,
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"Linking TBs %p [" TARGET_FMT_lx
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"] index %d -> %p [" TARGET_FMT_lx "]\n",
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tb->tc_ptr, tb->pc, n,
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tb_next->tc_ptr, tb_next->pc);
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/* patch the native jump address */
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tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc_ptr);
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/* add in TB jmp circular list */
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tb->jmp_list_next[n] = tb_next->jmp_list_first;
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tb_next->jmp_list_first = (uintptr_t)tb | n;
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if (tb->jmp_list_next[n]) {
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/* Another thread has already done this while we were
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* outside of the lock; nothing to do in this case */
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return;
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}
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qemu_log_mask_and_addr(CPU_LOG_EXEC, tb->pc,
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"Linking TBs %p [" TARGET_FMT_lx
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"] index %d -> %p [" TARGET_FMT_lx "]\n",
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tb->tc_ptr, tb->pc, n,
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tb_next->tc_ptr, tb_next->pc);
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/* patch the native jump address */
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tb_set_jmp_target(tb, n, (uintptr_t)tb_next->tc_ptr);
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/* add in TB jmp circular list */
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tb->jmp_list_next[n] = tb_next->jmp_list_first;
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tb_next->jmp_list_first = (uintptr_t)tb | n;
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}
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/* GETRA is the true target of the return instruction that we'll execute,
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