check cross-page block-linking

TranslationBlock has four members which are physical page related:

1. struct TranslationBlock *phys_hash_next     /* next matching tb for physical address. */ 
1. tb_phys_hash[] -> so called global TB mapping table, index by physical page address[2:17]
2. phys_hash_next: next TB in the link list of this entry

1. struct TranslationBlock *page_next; /*first and second physical page containing code. The lower bit  of the pointer tells the index in page_next[] */
1. defined in tb_alloc_page() called in tb_link_page() called in tb_gen_code().
2. page_next is used for a link list of TranslationBlocks in the SAME page.
3. PageDesc *p->first_tb points to the LAST TB in this page(the latest encountered.)
4. Why we have two page_next[]? Because, this TB could span across two pages, therefore, we need to page_next, one for the first page, and the next for the second.
5. Question: is it possible that more than two TB in the same page has two page_next? YES, when two translation blocks are overlapped.
6. 
   

1. tb_page_addr_t page_addr[2]
1. address of two pages. Stupid question: is it possible one TB across two different physical page? YES, although virtual addresses of pages are consecutive, they may not be  consecutive in physical pages.
2. 
   

    /* Circular List of TBs jumping to this one. This is a circular list using

       the two least significant bits of the pointers to tell what is

       the next pointer: 0 = jmp_next[0], 1 = jmp_next[1], 2 =

       jmp_first (tb itself)*/

1. struct TranslationBlock *jmp_next[2];
2. struct TranslationBlock *jmp_first;
1. Initialized in tb_link_page(), which is called in tb_gen_code(); Initially, it points to itself which set low bits to 2.
2. tb_add_jump(tb, n, tb_next) sets a jump from tb[n] to tb_next to tb;  tb[n]----tb_next.
3. Then set tb->jmp_next[n]  pointed to tb_next->jmp_first.
4. Then set tb_next->jmp_first to tb, and set low bits to n;
5. Illustration:

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tb_remove(ptb, tb, next_offset)

• Remove tb in hash tb link list.
• called in tb_phys_invalidate()

tb_page_remove(ptb, tb)

• Remove tb from page tb link list.
• called  in tb_phys_invalidate()

tb_jmp_remove(tb, n)

• Remove tb from tb jump circular list.
• called in tb_phys_invalidate()

tb_phys_invalidate(tb, page_addr)

• called from
• tb_invalidate_phys_page_range(start, end, is_cpu_write_access)
• tb_invalidate_phys_page(addr, pc, puc)
• Only in USER MODE.
• check_watchpoint(offset, len_mask, flags)
• cpu_io_recompile(env, retaddr)

tb_invalidate_phys_page_range(start, end, is_cpu_write_access)

• called from 
• tb_invalidate_phys_range(start, end, is_cpu_write_access)
• only called in linux-user/mmap.c
• tb_invalidate_phys_page_fast(start, len)
• use code_bitmap to quickly check whether there has tb in this range.
• called from notdirty_mem_write(opague, ram_addr, val, size)
• tb_invalidate_phys_addr(addr)
• only if TARGET_HAS_ICE
• cpu_physical_memory_rw(addr, buf, len, is_write)
• cpu_physical_memory_unmap(buffer, len, is_write, access_len)
• stl_phys_notdirty(addr, val)
• tb_invalidate_phys_page_range is called if in_migration
• stl_phys_internal(addr, val, endian)
• stw_phys_internal(addr, val, endian)
• called from stw_phys(), stw_le_phy()/*little endian*/, stw_be_phys()

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